The Spring Web model-view-controller (MVC) framework is designed around a
DispatcherServlet
that dispatches requests to handlers, with configurable handler
mappings, view resolution, locale, time zone and theme resolution as well as support for
uploading files. The default handler is based on the @Controller
and @RequestMapping
annotations, offering a wide range of flexible handling methods. With the introduction
of Spring 3.0, the @Controller
mechanism also allows you to create RESTful Web sites
and applications, through the @PathVariable
annotation and other features.
In Spring Web MVC you can use any object as a command or form-backing object; you do not need to implement a framework-specific interface or base class. Spring’s data binding is highly flexible: for example, it treats type mismatches as validation errors that can be evaluated by the application, not as system errors. Thus you need not duplicate your business objects' properties as simple, untyped strings in your form objects simply to handle invalid submissions, or to convert the Strings properly. Instead, it is often preferable to bind directly to your business objects.
Spring’s view resolution is extremely flexible. A Controller
is typically responsible
for preparing a model Map
with data and selecting a view name but it can also write
directly to the response stream and complete the request. View name resolution is highly
configurable through file extension or Accept header content type negotiation, through
bean names, a properties file, or even a custom ViewResolver
implementation. The model
(the M in MVC) is a Map
interface, which allows for the complete abstraction of the
view technology. You can integrate directly with template based rendering technologies
such as JSP, Velocity and Freemarker, or directly generate XML, JSON, Atom, and many
other types of content. The model Map
is simply transformed into an appropriate
format, such as JSP request attributes, a Velocity template model.
Spring’s web module includes many unique web support features:
DispatcherServlet
, handler mapping, view resolver, and so
on — can be fulfilled by a specialized object.
Map
supports easy
integration with any view technology.
Session
.
This is not a specific feature of Spring MVC itself, but rather of the
WebApplicationContext
container(s) that Spring MVC uses. These bean scopes are
described in Section 6.5.4, “Request, session, and global session scopes”
Non-Spring MVC implementations are preferable for some projects. Many teams expect to leverage their existing investment in skills and tools, for example with JSF.
If you do not want to use Spring’s Web MVC, but intend to leverage other solutions that
Spring offers, you can integrate the web MVC framework of your choice with Spring
easily. Simply start up a Spring root application context through its
ContextLoaderListener
, and access it through its ServletContext
attribute (or
Spring’s respective helper method) from within any action object. No "plug-ins"
are involved, so no dedicated integration is necessary. From the web layer’s point of
view, you simply use Spring as a library, with the root application context instance as
the entry point.
Your registered beans and Spring’s services can be at your fingertips even without Spring’s Web MVC. Spring does not compete with other web frameworks in this scenario. It simply addresses the many areas that the pure web MVC frameworks do not, from bean configuration to data access and transaction handling. So you can enrich your application with a Spring middle tier and/or data access tier, even if you just want to use, for example, the transaction abstraction with JDBC or Hibernate.
Spring’s web MVC framework is, like many other web MVC frameworks, request-driven,
designed around a central Servlet that dispatches requests to controllers and offers
other functionality that facilitates the development of web applications. Spring’s
DispatcherServlet
however, does more than just that. It is completely integrated with
the Spring IoC container and as such allows you to use every other feature that Spring
has.
The request processing workflow of the Spring Web MVC DispatcherServlet
is illustrated
in the following diagram. The pattern-savvy reader will recognize that the
DispatcherServlet
is an expression of the "Front Controller" design pattern (this is a
pattern that Spring Web MVC shares with many other leading web frameworks).
The DispatcherServlet
is an actual Servlet
(it inherits from the HttpServlet
base
class), and as such is declared in the web.xml
of your web application. You need to
map requests that you want the DispatcherServlet
to handle, by using a URL mapping in
the same web.xml
file. This is standard Java EE Servlet configuration; the following
example shows such a DispatcherServlet
declaration and mapping:
<web-app> <servlet> <servlet-name>example</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>example</servlet-name> <url-pattern>/example/*</url-pattern> </servlet-mapping> </web-app>
In the preceding example, all requests starting with /example
will be handled by the
DispatcherServlet
instance named example
. In a Servlet 3.0+ environment, you also
have the option of configuring the Servlet container programmatically. Below is the code
based equivalent of the above web.xml
example:
public class MyWebApplicationInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet()); registration.setLoadOnStartup(1); registration.addMapping("/example/*"); } }
WebApplicationInitializer
is an interface provided by Spring MVC that ensures your
code-based configuration is detected and automatically used to initialize any Servlet 3
container. An abstract base class implementation of this interface named
AbstractDispatcherServletInitializer
makes it even easier to register the
DispatcherServlet
by simply specifying its servlet mapping.
See Code-based Servlet container initialization for more details.
The above is only the first step in setting up Spring Web MVC. You now need to configure
the various beans used by the Spring Web MVC framework (over and above the
DispatcherServlet
itself).
As detailed in Section 6.15, “Additional Capabilities of the ApplicationContext”, ApplicationContext
instances in Spring can be
scoped. In the Web MVC framework, each DispatcherServlet
has its own
WebApplicationContext
, which inherits all the beans already defined in the root
WebApplicationContext
. These inherited beans can be overridden in the servlet-specific
scope, and you can define new scope-specific beans local to a given Servlet instance.
Upon initialization of a DispatcherServlet
, Spring MVC looks for a file named
[servlet-name]-servlet.xml in the WEB-INF
directory of your web application and
creates the beans defined there, overriding the definitions of any beans defined with
the same name in the global scope.
Consider the following DispatcherServlet
Servlet configuration (in the web.xml
file):
<web-app> <servlet> <servlet-name>golfing</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>golfing</servlet-name> <url-pattern>/golfing/*</url-pattern> </servlet-mapping> </web-app>
With the above Servlet configuration in place, you will need to have a file called
/WEB-INF/golfing-servlet.xml
in your application; this file will contain all of your
Spring Web MVC-specific components (beans). You can change the exact location of this
configuration file through a Servlet initialization parameter (see below for details).
It is also possible to have just one root context for single DispatcherServlet scenarios.
This can be configured by setting an empty contextConfigLocation servlet init parameter, as shown below:
<web-app> <context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/root-context.xml</param-value> </context-param> <servlet> <servlet-name>dispatcher</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <init-param> <param-name>contextConfigLocation</param-name> <param-value></param-value> </init-param> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>dispatcher</servlet-name> <url-pattern>/*</url-pattern> </servlet-mapping> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> </web-app>
The WebApplicationContext
is an extension of the plain ApplicationContext
that has
some extra features necessary for web applications. It differs from a normal
ApplicationContext
in that it is capable of resolving themes (see
Section 21.9, “Using themes”), and that it knows which Servlet it is associated with (by having
a link to the ServletContext
). The WebApplicationContext
is bound in the
ServletContext
, and by using static methods on the RequestContextUtils
class you can
always look up the WebApplicationContext
if you need access to it.
The Spring DispatcherServlet
uses special beans to process requests and render the
appropriate views. These beans are part of Spring MVC. You can choose which special
beans to use by simply configuring one or more of them in the WebApplicationContext
.
However, you don’t need to do that initially since Spring MVC maintains a list of
default beans to use if you don’t configure any. More on that in the next section. First
see the table below listing the special bean types the DispatcherServlet
relies on.
Table 21.1. Special bean types in the WebApplicationContext
Bean type | Explanation |
---|---|
Maps incoming requests to handlers and a list of pre- and post-processors (handler
interceptors) based on some criteria the details of which vary by | |
HandlerAdapter | Helps the |
Maps exceptions to views also allowing for more complex exception handling code. | |
Resolves logical String-based view names to actual | |
Resolves the locale a client is using and possibly their time zone, in order to be able to offer internationalized views | |
Resolves themes your web application can use, for example, to offer personalized layouts | |
Parses multi-part requests for example to support processing file uploads from HTML forms. | |
Stores and retrieves the "input" and the "output" |
As mentioned in the previous section for each special bean the DispatcherServlet
maintains a list of implementations to use by default. This information is kept in the
file DispatcherServlet.properties
in the package org.springframework.web.servlet
.
All special beans have some reasonable defaults of their own. Sooner or later though
you’ll need to customize one or more of the properties these beans provide. For example
it’s quite common to configure an InternalResourceViewResolver
settings its prefix
property to the parent location of view files.
Regardless of the details, the important concept to understand here is that once
you configure a special bean such as an InternalResourceViewResolver
in your
WebApplicationContext
, you effectively override the list of default implementations
that would have been used otherwise for that special bean type. For example if you
configure an InternalResourceViewResolver
, the default list of ViewResolver
implementations is ignored.
In Section 21.16, “Configuring Spring MVC” you’ll learn about other options for configuring Spring MVC including MVC Java config and the MVC XML namespace both of which provide a simple starting point and assume little knowledge of how Spring MVC works. Regardless of how you choose to configure your application, the concepts explained in this section are fundamental should be of help to you.
After you set up a DispatcherServlet
, and a request comes in for that specific
DispatcherServlet
, the DispatcherServlet
starts processing the request as follows:
WebApplicationContext
is searched for and bound in the request as an attribute
that the controller and other elements in the process can use. It is bound by default
under the key DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE
.
MultipartHttpServletRequest
for
further processing by other elements in the process. See Section 21.10, “Spring’s multipart (file upload) support” for further
information about multipart handling.
Handler exception resolvers that are declared in the WebApplicationContext
pick up
exceptions that are thrown during processing of the request. Using these exception
resolvers allows you to define custom behaviors to address exceptions.
The Spring DispatcherServlet
also supports the return of the
last-modification-date, as specified by the Servlet API. The process of determining
the last modification date for a specific request is straightforward: the
DispatcherServlet
looks up an appropriate handler mapping and tests whether the
handler that is found implements the LastModified interface. If so, the value of the
long getLastModified(request)
method of the LastModified
interface is returned to
the client.
You can customize individual DispatcherServlet
instances by adding Servlet
initialization parameters ( init-param
elements) to the Servlet declaration in the
web.xml
file. See the following table for the list of supported parameters.
Table 21.2. DispatcherServlet initialization parameters
Parameter | Explanation |
---|---|
| Class that implements |
| String that is passed to the context instance (specified by |
| Namespace of the |
Controllers provide access to the application behavior that you typically define through a service interface. Controllers interpret user input and transform it into a model that is represented to the user by the view. Spring implements a controller in a very abstract way, which enables you to create a wide variety of controllers.
Spring 2.5 introduced an annotation-based programming model for MVC controllers that
uses annotations such as @RequestMapping
, @RequestParam
, @ModelAttribute
, and so
on. This annotation support is available for both Servlet MVC and Portlet MVC.
Controllers implemented in this style do not have to extend specific base classes or
implement specific interfaces. Furthermore, they do not usually have direct dependencies
on Servlet or Portlet APIs, although you can easily configure access to Servlet or
Portlet facilities.
Tip | |
---|---|
Available in the spring-projects Org on Github, a number of web applications leverage the annotation support described in this section including MvcShowcase, MvcAjax, MvcBasic, PetClinic, PetCare, and others. |
@Controller public class HelloWorldController { @RequestMapping("/helloWorld") public String helloWorld(Model model) { model.addAttribute("message", "Hello World!"); return "helloWorld"; } }
As you can see, the @Controller
and @RequestMapping
annotations allow flexible
method names and signatures. In this particular example the method accepts a Model
and
returns a view name as a String
, but various other method parameters and return values
can be used as explained later in this section. @Controller
and @RequestMapping
and
a number of other annotations form the basis for the Spring MVC implementation. This
section documents these annotations and how they are most commonly used in a Servlet
environment.
The @Controller
annotation indicates that a particular class serves the role of
a controller. Spring does not require you to extend any controller base class or
reference the Servlet API. However, you can still reference Servlet-specific features if
you need to.
The @Controller
annotation acts as a stereotype for the annotated class, indicating
its role. The dispatcher scans such annotated classes for mapped methods and detects
@RequestMapping
annotations (see the next section).
You can define annotated controller beans explicitly, using a standard Spring bean
definition in the dispatcher’s context. However, the @Controller
stereotype also
allows for autodetection, aligned with Spring general support for detecting component
classes in the classpath and auto-registering bean definitions for them.
To enable autodetection of such annotated controllers, you add component scanning to your configuration. Use the spring-context schema as shown in the following XML snippet:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="org.springframework.samples.petclinic.web"/> <!-- ... --> </beans>
You use the @RequestMapping
annotation to map URLs such as /appointments
onto an
entire class or a particular handler method. Typically the class-level annotation maps a
specific request path (or path pattern) onto a form controller, with additional
method-level annotations narrowing the primary mapping for a specific HTTP method
request method ("GET", "POST", etc.) or an HTTP request parameter condition.
The following example from the Petcare sample shows a controller in a Spring MVC application that uses this annotation:
@Controller @RequestMapping("/appointments") public class AppointmentsController { private final AppointmentBook appointmentBook; @Autowired public AppointmentsController(AppointmentBook appointmentBook) { this.appointmentBook = appointmentBook; } @RequestMapping(method = RequestMethod.GET) public Map<String, Appointment> get() { return appointmentBook.getAppointmentsForToday(); } @RequestMapping(path = "/{day}", method = RequestMethod.GET) public Map<String, Appointment> getForDay(@PathVariable @DateTimeFormat(iso=ISO.DATE) Date day, Model model) { return appointmentBook.getAppointmentsForDay(day); } @RequestMapping(path = "/new", method = RequestMethod.GET) public AppointmentForm getNewForm() { return new AppointmentForm(); } @RequestMapping(method = RequestMethod.POST) public String add(@Valid AppointmentForm appointment, BindingResult result) { if (result.hasErrors()) { return "appointments/new"; } appointmentBook.addAppointment(appointment); return "redirect:/appointments"; } }
In the example, the @RequestMapping
is used in a number of places. The first usage is
on the type (class) level, which indicates that all handling methods on this controller
are relative to the /appointments
path. The get()
method has a further
@RequestMapping
refinement: it only accepts GET requests, meaning that an HTTP GET for
/appointments
invokes this method. The add()
has a similar refinement, and the
getNewForm()
combines the definition of HTTP method and path into one, so that GET
requests for appointments/new
are handled by that method.
The getForDay()
method shows another usage of @RequestMapping
: URI templates. (See
the next section).
A @RequestMapping
on the class level is not required. Without it, all paths are simply
absolute, and not relative. The following example from the PetClinic sample
application shows a multi-action controller using @RequestMapping
:
@Controller public class ClinicController { private final Clinic clinic; @Autowired public ClinicController(Clinic clinic) { this.clinic = clinic; } @RequestMapping("/") public void welcomeHandler() { } @RequestMapping("/vets") public ModelMap vetsHandler() { return new ModelMap(this.clinic.getVets()); } }
The above example does not specify GET vs. PUT, POST, and so forth, because
@RequestMapping
maps all HTTP methods by default. Use @RequestMapping(method=GET)
to narrow the mapping.
In some cases a controller may need to be decorated with an AOP proxy at runtime.
One example is if you choose to have @Transactional
annotations directly on the
controller. When this is the case, for controllers specifically, we recommend
using class-based proxying. This is typically the default choice with controllers.
However if a controller must implement an interface that is not a Spring Context
callback (e.g. InitializingBean
, *Aware
, etc), you may need to explicitly
configure class-based proxying. For example with <tx:annotation-driven />
,
change to <tx:annotation-driven proxy-target-class="true" />
.
Spring 3.1 introduced a new set of support classes for @RequestMapping
methods called
RequestMappingHandlerMapping
and RequestMappingHandlerAdapter
respectively. They are
recommended for use and even required to take advantage of new features in Spring MVC
3.1 and going forward. The new support classes are enabled by default by the MVC
namespace and the MVC Java config but must be configured explicitly if using neither.
This section describes a few important differences between the old and the new support
classes.
Prior to Spring 3.1, type and method-level request mappings were examined in two
separate stages — a controller was selected first by the
DefaultAnnotationHandlerMapping
and the actual method to invoke was narrowed down
second by the AnnotationMethodHandlerAdapter
.
With the new support classes in Spring 3.1, the RequestMappingHandlerMapping
is the
only place where a decision is made about which method should process the request. Think
of controller methods as a collection of unique endpoints with mappings for each method
derived from type and method-level @RequestMapping
information.
This enables some new possibilities. For once a HandlerInterceptor
or a
HandlerExceptionResolver
can now expect the Object-based handler to be a
HandlerMethod
, which allows them to examine the exact method, its parameters and
associated annotations. The processing for a URL no longer needs to be split across
different controllers.
There are also several things no longer possible:
SimpleUrlHandlerMapping
or
BeanNameUrlHandlerMapping
and then narrow the method based on @RequestMapping
annotations.
@RequestMapping
methods that don’t have an explicit path mapping URL path but
otherwise match equally, e.g. by HTTP method. In the new support classes
@RequestMapping
methods have to be mapped uniquely.
The above features are still supported with the existing support classes. However to take advantage of new Spring MVC 3.1 features you’ll need to use the new support classes.
URI templates can be used for convenient access to selected parts of a URL in a
@RequestMapping
method.
A URI Template is a URI-like string, containing one or more variable names. When you
substitute values for these variables, the template becomes a URI. The
proposed RFC for URI Templates defines
how a URI is parameterized. For example, the URI Template
http://www.example.com/users/{userId}
contains the variable userId. Assigning the
value fred to the variable yields http://www.example.com/users/fred
.
In Spring MVC you can use the @PathVariable
annotation on a method argument to bind it
to the value of a URI template variable:
@RequestMapping(path="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable String ownerId, Model model) { Owner owner = ownerService.findOwner(ownerId); model.addAttribute("owner", owner); return "displayOwner"; }
The URI Template " /owners/{ownerId}`" specifies the variable name `ownerId
. When the
controller handles this request, the value of ownerId
is set to the value found in the
appropriate part of the URI. For example, when a request comes in for /owners/fred
,
the value of ownerId
is fred
.
Tip | |
---|---|
To process the @PathVariable annotation, Spring MVC needs to find the matching URI template variable by name. You can specify it in the annotation: @RequestMapping(path="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable("ownerId") String theOwner, Model model) { // implementation omitted } Or if the URI template variable name matches the method argument name you can omit that detail. As long as your code is not compiled without debugging information, Spring MVC will match the method argument name to the URI template variable name: @RequestMapping(path="/owners/{ownerId}", method=RequestMethod.GET) public String findOwner(@PathVariable String ownerId, Model model) { // implementation omitted } |
A method can have any number of @PathVariable
annotations:
@RequestMapping(path="/owners/{ownerId}/pets/{petId}", method=RequestMethod.GET) public String findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { Owner owner = ownerService.findOwner(ownerId); Pet pet = owner.getPet(petId); model.addAttribute("pet", pet); return "displayPet"; }
When a @PathVariable
annotation is used on a Map<String, String>
argument, the map
is populated with all URI template variables.
A URI template can be assembled from type and path level @RequestMapping
annotations. As a result the findPet()
method can be invoked with a URL such as
/owners/42/pets/21
.
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping("/pets/{petId}") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
A @PathVariable
argument can be of any simple type such as int, long, Date, etc.
Spring automatically converts to the appropriate type or throws a
TypeMismatchException
if it fails to do so. You can also register support for parsing
additional data types. See the section called “Method Parameters And Type Conversion” and the section called “Customizing WebDataBinder initialization”.
Sometimes you need more precision in defining URI template variables. Consider the URL
"/spring-web/spring-web-3.0.5.jar"
. How do you break it down into multiple parts?
The @RequestMapping
annotation supports the use of regular expressions in URI template
variables. The syntax is {varName:regex}
where the first part defines the variable
name and the second - the regular expression.For example:
@RequestMapping("/spring-web/{symbolicName:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{extension:\\.[a-z]+}") public void handle(@PathVariable String version, @PathVariable String extension) { // ... } }
In addition to URI templates, the @RequestMapping
annotation also supports Ant-style
path patterns (for example, /myPath/*.do
). A combination of URI template variables and
Ant-style globs is also supported (e.g. /owners/*/pets/{petId}
).
When a URL matches multiple patterns, a sort is used to find the most specific match.
A pattern with a lower count of URI variables and wild cards is considered more specific.
For example /hotels/{hotel}/*
has 1 URI variable and 1 wild card and is considered
more specific than /hotels/{hotel}/**
which as 1 URI variable and 2 wild cards.
If two patterns have the same count, the one that is longer is considered more specific.
For example /foo/bar*
is longer and considered more specific than /foo/*
.
When two patterns have the same count and length, the pattern with fewer wild cards is considered more specific.
For example /hotels/{hotel}
is more specific than /hotels/*
.
There are also some additional special rules:
/**
is less specific than any other pattern.
For example /api/{a}/{b}/{c}
is more specific.
/public/**
is less specific than any other pattern that doesn’t contain double wildcards.
For example /public/path3/{a}/{b}/{c}
is more specific.
For the full details see AntPatternComparator
in AntPathMatcher
. Note that the PathMatcher
can be customized (see Section 21.16.11, “Path Matching” in the section on configuring Spring MVC).
Patterns in @RequestMapping
annotations support ${…} placeholders against local
properties and/or system properties and environment variables. This may be useful in
cases where the path a controller is mapped to may need to be customized through
configuration. For more information on placeholders, see the javadocs of the
PropertyPlaceholderConfigurer
class.
By default Spring MVC automatically performs ".*"
suffix pattern matching so
that a controller mapped to /person
is also implicitly mapped to /person.*
.
This allows indicating content types via file extensions, e.g. /person.pdf
,
/person.xml
, etc. A common pitfall however is when the last path segment of the
mapping is a URI variable, e.g. /person/{id}
. While a request for /person/1.json
would correctly result in path variable id=1 and extension ".json", when the id
naturally contains a dot, e.g. /person/joe@email.com
the result does not match
expectations. Clearly here ".com" is not a file extension.
The proper way to address this is to configure Spring MVC to only do suffix pattern matching against file extensions registered for content negotiation purposes. For more on this, first see Section 21.16.6, “Content Negotiation” and then Section 21.16.11, “Path Matching” showing how to enable suffix pattern matching along with how to use registered suffix patterns only.
The URI specification RFC 3986 defines the possibility of including name-value pairs within path segments. There is no specific term used in the spec. The general "URI path parameters" could be applied although the more unique "Matrix URIs", originating from an old post by Tim Berners-Lee, is also frequently used and fairly well known. Within Spring MVC these are referred to as matrix variables.
Matrix variables can appear in any path segment, each matrix variable separated with a
";" (semicolon). For example: "/cars;color=red;year=2012"
. Multiple values may be
either "," (comma) separated "color=red,green,blue"
or the variable name may be
repeated "color=red;color=green;color=blue"
.
If a URL is expected to contain matrix variables, the request mapping pattern must represent them with a URI template. This ensures the request can be matched correctly regardless of whether matrix variables are present or not and in what order they are provided.
Below is an example of extracting the matrix variable "q":
// GET /pets/42;q=11;r=22 @RequestMapping(path = "/pets/{petId}", method = RequestMethod.GET) public void findPet(@PathVariable String petId, @MatrixVariable int q) { // petId == 42 // q == 11 }
Since all path segments may contain matrix variables, in some cases you need to be more specific to identify where the variable is expected to be:
// GET /owners/42;q=11/pets/21;q=22 @RequestMapping(path = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET) public void findPet( @MatrixVariable(name="q", pathVar="ownerId") int q1, @MatrixVariable(name="q", pathVar="petId") int q2) { // q1 == 11 // q2 == 22 }
A matrix variable may be defined as optional and a default value specified:
// GET /pets/42 @RequestMapping(path = "/pets/{petId}", method = RequestMethod.GET) public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) { // q == 1 }
All matrix variables may be obtained in a Map:
// GET /owners/42;q=11;r=12/pets/21;q=22;s=23 @RequestMapping(path = "/owners/{ownerId}/pets/{petId}", method = RequestMethod.GET) public void findPet( @MatrixVariable Map<String, String> matrixVars, @MatrixVariable(pathVar="petId"") Map<String, String> petMatrixVars) { // matrixVars: ["q" : [11,22], "r" : 12, "s" : 23] // petMatrixVars: ["q" : 11, "s" : 23] }
Note that to enable the use of matrix variables, you must set the
removeSemicolonContent
property of RequestMappingHandlerMapping
to false
. By
default it is set to true
.
Tip | |
---|---|
The MVC Java config and the MVC namespace both provide options for enabling the use of matrix variables. If you are using Java config, The Advanced Customizations
with MVC Java Config section describes how the In the MVC namespace, the <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <mvc:annotation-driven enable-matrix-variables="true"/> </beans> |
You can narrow the primary mapping by specifying a list of consumable media types. The request will be matched only if the Content-Type request header matches the specified media type. For example:
@Controller @RequestMapping(path = "/pets", method = RequestMethod.POST, consumes="application/json") public void addPet(@RequestBody Pet pet, Model model) { // implementation omitted }
Consumable media type expressions can also be negated as in !text/plain to match to all requests other than those with Content-Type of text/plain.
Tip | |
---|---|
The consumes condition is supported on the type and on the method level. Unlike most other conditions, when used at the type level, method-level consumable types override rather than extend type-level consumable types. |
You can narrow the primary mapping by specifying a list of producible media types. The request will be matched only if the Accept request header matches one of these values. Furthermore, use of the produces condition ensures the actual content type used to generate the response respects the media types specified in the produces condition. For example:
@Controller @RequestMapping(path = "/pets/{petId}", method = RequestMethod.GET, produces="application/json") @ResponseBody public Pet getPet(@PathVariable String petId, Model model) { // implementation omitted }
Just like with consumes, producible media type expressions can be negated as in !text/plain to match to all requests other than those with an Accept header value of text/plain.
Tip | |
---|---|
The produces condition is supported on the type and on the method level. Unlike most other conditions, when used at the type level, method-level producible types override rather than extend type-level producible types. |
You can narrow request matching through request parameter conditions such as
"myParam"
, "!myParam"
, or "myParam=myValue"
. The first two test for request
parameter presence/absence and the third for a specific parameter value. Here is an
example with a request parameter value condition:
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping(path = "/pets/{petId}", method = RequestMethod.GET, params="myParam=myValue") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
The same can be done to test for request header presence/absence or to match based on a specific request header value:
@Controller @RequestMapping("/owners/{ownerId}") public class RelativePathUriTemplateController { @RequestMapping(path = "/pets", method = RequestMethod.GET, headers="myHeader=myValue") public void findPet(@PathVariable String ownerId, @PathVariable String petId, Model model) { // implementation omitted } }
Tip | |
---|---|
Although you can match to Content-Type and Accept header values using media type wild cards (for example "content-type=text/*" will match to "text/plain" and "text/html"), it is recommended to use the consumes and produces conditions respectively instead. They are intended specifically for that purpose. |
An @RequestMapping
handler method can have a very flexible signatures. The supported
method arguments and return values are described in the following section. Most
arguments can be used in arbitrary order with the only exception of BindingResult
arguments. This is described in the next section.
Note | |
---|---|
Spring 3.1 introduced a new set of support classes for |
The following are the supported method arguments:
ServletRequest
or HttpServletRequest
.
HttpSession
. An argument of this type enforces
the presence of a corresponding session. As a consequence, such an argument is never
null
.
Note | |
---|---|
Session access may not be thread-safe, in particular in a Servlet environment. Consider setting the RequestMappingHandlerAdapter's "synchronizeOnSession" flag to "true" if multiple requests are allowed to access a session concurrently. |
org.springframework.web.context.request.WebRequest
or
org.springframework.web.context.request.NativeWebRequest
. Allows for generic
request parameter access as well as request/session attribute access, without ties
to the native Servlet/Portlet API.
java.util.Locale
for the current request locale, determined by the most specific
locale resolver available, in effect, the configured LocaleResolver
/
LocaleContextResolver
in an MVC environment.
java.util.TimeZone
(Java 6+) / java.time.ZoneId
(on Java 8) for the time zone
associated with the current request, as determined by a LocaleContextResolver
.
java.io.InputStream
/ java.io.Reader
for access to the request’s content.
This value is the raw InputStream/Reader as exposed by the Servlet API.
java.io.OutputStream
/ java.io.Writer
for generating the response’s content.
This value is the raw OutputStream/Writer as exposed by the Servlet API.
org.springframework.http.HttpMethod
for the HTTP request method.
java.security.Principal
containing the currently authenticated user.
@PathVariable
annotated parameters for access to URI template variables. See
the section called “URI Template Patterns”.
@MatrixVariable
annotated parameters for access to name-value pairs located in
URI path segments. See the section called “Matrix Variables”.
@RequestParam
annotated parameters for access to specific Servlet request
parameters. Parameter values are converted to the declared method argument type.
See the section called “Binding request parameters to method parameters with @RequestParam”.
@RequestHeader
annotated parameters for access to specific Servlet request HTTP
headers. Parameter values are converted to the declared method argument type.
See the section called “Mapping request header attributes with the @RequestHeader annotation”.
@RequestBody
annotated parameters for access to the HTTP request body. Parameter
values are converted to the declared method argument type using
HttpMessageConverters. See the section called “Mapping the request body with the @RequestBody annotation”.
@RequestPart
annotated parameters for access to the content of a
"multipart/form-data" request part. See Section 21.10.5, “Handling a file upload request from programmatic clients” and
Section 21.10, “Spring’s multipart (file upload) support”.
HttpEntity<?>
parameters for access to the Servlet request HTTP headers and
contents. The request stream will be converted to the entity body using
HttpMessageConverters. See the section called “Using HttpEntity”.
java.util.Map
/ org.springframework.ui.Model
/ org.springframework.ui.ModelMap
for enriching the implicit model that is exposed to the web view.
org.springframework.web.servlet.mvc.support.RedirectAttributes
to specify the exact
set of attributes to use in case of a redirect and also to add flash attributes
(attributes stored temporarily on the server-side to make them available to the
request after the redirect). See the section called “Passing Data To the Redirect Target” and
Section 21.6, “Using flash attributes”.
@InitBinder
methods and/or the HandlerAdapter configuration. See the webBindingInitializer
property on RequestMappingHandlerAdapter
. Such command objects along with their
validation results will be exposed as model attributes by default, using the command
class class name - e.g. model attribute "orderAddress" for a command object of type
"some.package.OrderAddress". The ModelAttribute
annotation can be used on a method
argument to customize the model attribute name used.
org.springframework.validation.Errors
/
org.springframework.validation.BindingResult
validation results for a preceding
command or form object (the immediately preceding method argument).
org.springframework.web.bind.support.SessionStatus
status handle for marking form
processing as complete, which triggers the cleanup of session attributes that have
been indicated by the @SessionAttributes
annotation at the handler type level.
org.springframework.web.util.UriComponentsBuilder
a builder for preparing a URL
relative to the current request’s host, port, scheme, context path, and the literal
part of the servlet mapping.
The Errors
or BindingResult
parameters have to follow the model object that is being
bound immediately as the method signature might have more that one model object and
Spring will create a separate BindingResult
instance for each of them so the following
sample won’t work:
Invalid ordering of BindingResult and @ModelAttribute.
@RequestMapping(method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, Model model, BindingResult result) { ... }
Note, that there is a Model
parameter in between Pet
and BindingResult
. To get
this working you have to reorder the parameters as follows:
@RequestMapping(method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result, Model model) { ... }
Note | |
---|---|
JDK 1.8’s |
The following are the supported return types:
ModelAndView
object, with the model implicitly enriched with command objects and
the results of @ModelAttribute
annotated reference data accessor methods.
Model
object, with the view name implicitly determined through a
RequestToViewNameTranslator
and the model implicitly enriched with command objects
and the results of @ModelAttribute
annotated reference data accessor methods.
Map
object for exposing a model, with the view name implicitly determined through
a RequestToViewNameTranslator
and the model implicitly enriched with command objects
and the results of @ModelAttribute
annotated reference data accessor methods.
View
object, with the model implicitly determined through command objects and
@ModelAttribute
annotated reference data accessor methods. The handler method may
also programmatically enrich the model by declaring a Model
argument (see above).
String
value that is interpreted as the logical view name, with the model
implicitly determined through command objects and @ModelAttribute
annotated
reference data accessor methods. The handler method may also programmatically enrich
the model by declaring a Model
argument (see above).
void
if the method handles the response itself (by writing the response content
directly, declaring an argument of type ServletResponse
/ HttpServletResponse
for
that purpose) or if the view name is supposed to be implicitly determined through a
RequestToViewNameTranslator
(not declaring a response argument in the handler method
signature).
@ResponseBody
, the return type is written to the
response HTTP body. The return value will be converted to the declared method argument
type using HttpMessageConverters. See the section called “Mapping the response body with the @ResponseBody annotation”.
HttpEntity<?>
or ResponseEntity<?>
object to provide access to the Servlet
response HTTP headers and contents. The entity body will be converted to the response
stream using HttpMessageConverters. See the section called “Using HttpEntity”.
HttpHeaders
object to return a response with no body.
Callable<?>
can be returned when the application wants to produce the return value
asynchronously in a thread managed by Spring MVC.
DeferredResult<?>
can be returned when the application wants to produce the return
value from a thread of its own choosing.
ListenableFuture<?>
can be returned when the application wants to produce the return
value from a thread of its own choosing.
ResponseBodyEmitter
can be returned to write multiple objects to the response
asynchronously; also supported as the body within a ResponseEntity
.
SseEmitter
can be returned to write Server-Sent Events to the response
asynchronously; also supported as the body within a ResponseEntity
.
StreamingResponseBody
can be returned to write to the response OutputStream
asynchronously; also supported as the body within a ResponseEntity
.
@ModelAttribute
at the method
level (or the default attribute name based on the return type class name). The model
is implicitly enriched with command objects and the results of @ModelAttribute
annotated reference data accessor methods.
Use the @RequestParam
annotation to bind request parameters to a method parameter in
your controller.
The following code snippet shows the usage:
@Controller @RequestMapping("/pets") @SessionAttributes("pet") public class EditPetForm { // ... @RequestMapping(method = RequestMethod.GET) public String setupForm(@RequestParam("petId") int petId, ModelMap model) { Pet pet = this.clinic.loadPet(petId); model.addAttribute("pet", pet); return "petForm"; } // ... }
Parameters using this annotation are required by default, but you can specify that a
parameter is optional by setting @RequestParam's required
attribute to false
(e.g., @RequestParam(path="id", required=false)
).
Type conversion is applied automatically if the target method parameter type is not
String
. See the section called “Method Parameters And Type Conversion”.
When an @RequestParam
annotation is used on a Map<String, String>
or
MultiValueMap<String, String>
argument, the map is populated with all request
parameters.
The @RequestBody
method parameter annotation indicates that a method parameter should
be bound to the value of the HTTP request body. For example:
@RequestMapping(path = "/something", method = RequestMethod.PUT) public void handle(@RequestBody String body, Writer writer) throws IOException { writer.write(body); }
You convert the request body to the method argument by using an HttpMessageConverter
.
HttpMessageConverter
is responsible for converting from the HTTP request message to an
object and converting from an object to the HTTP response body. The
RequestMappingHandlerAdapter
supports the @RequestBody
annotation with the following
default HttpMessageConverters
:
ByteArrayHttpMessageConverter
converts byte arrays.
StringHttpMessageConverter
converts strings.
FormHttpMessageConverter
converts form data to/from a MultiValueMap<String, String>.
SourceHttpMessageConverter
converts to/from a javax.xml.transform.Source.
For more information on these converters, see Message Converters. Also note that if using the MVC namespace or the MVC Java config, a wider range of message converters are registered by default. See Section 21.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” for more information.
If you intend to read and write XML, you will need to configure the
MarshallingHttpMessageConverter
with a specific Marshaller
and an Unmarshaller
implementation from the org.springframework.oxm
package. The example below shows how
to do that directly in your configuration but if your application is configured through
the MVC namespace or the MVC Java config see Section 21.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” instead.
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="messageConverters"> <util:list id="beanList"> <ref bean="stringHttpMessageConverter"/> <ref bean="marshallingHttpMessageConverter"/> </util:list> </property </bean> <bean id="stringHttpMessageConverter" class="org.springframework.http.converter.StringHttpMessageConverter"/> <bean id="marshallingHttpMessageConverter" class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter"> <property name="marshaller" ref="castorMarshaller" /> <property name="unmarshaller" ref="castorMarshaller" /> </bean> <bean id="castorMarshaller" class="org.springframework.oxm.castor.CastorMarshaller"/>
An @RequestBody
method parameter can be annotated with @Valid
, in which case it will
be validated using the configured Validator
instance. When using the MVC namespace or
the MVC Java config, a JSR-303 validator is configured automatically assuming a JSR-303
implementation is available on the classpath.
Just like with @ModelAttribute
parameters, an Errors
argument can be used to examine
the errors. If such an argument is not declared, a MethodArgumentNotValidException
will be raised. The exception is handled in the DefaultHandlerExceptionResolver
, which
sends a 400
error back to the client.
Note | |
---|---|
Also see Section 21.16.1, “Enabling the MVC Java Config or the MVC XML Namespace” for information on configuring message converters and a validator through the MVC namespace or the MVC Java config. |
The @ResponseBody
annotation is similar to @RequestBody
. This annotation can be put
on a method and indicates that the return type should be written straight to the HTTP
response body (and not placed in a Model, or interpreted as a view name). For example:
@RequestMapping(path = "/something", method = RequestMethod.PUT) @ResponseBody public String helloWorld() { return "Hello World"; }
The above example will result in the text Hello World
being written to the HTTP
response stream.
As with @RequestBody
, Spring converts the returned object to a response body by using
an HttpMessageConverter
. For more information on these converters, see the previous
section and Message Converters.
It’s a very common use case to have Controllers implement a REST API, thus serving only
JSON, XML or custom MediaType content. For convenience, instead of annotating all your
@RequestMapping
methods with @ResponseBody
, you can annotate your Controller Class
with @RestController
.
@RestController
is a stereotype annotation that combines @ResponseBody
and @Controller
. More than
that, it gives more meaning to your Controller and also may carry additional semantics
in future releases of the framework.
As with regular @Controllers, a @RestController
may be assisted by a
@ControllerAdvice
Bean. See the the section called “Advising controllers with @ControllerAdvice” section for more details.
The HttpEntity
is similar to @RequestBody
and @ResponseBody
. Besides getting
access to the request and response body, HttpEntity
(and the response-specific
subclass ResponseEntity
) also allows access to the request and response headers, like
so:
@RequestMapping("/something") public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws UnsupportedEncodingException { String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader")); byte[] requestBody = requestEntity.getBody(); // do something with request header and body HttpHeaders responseHeaders = new HttpHeaders(); responseHeaders.set("MyResponseHeader", "MyValue"); return new ResponseEntity<String>("Hello World", responseHeaders, HttpStatus.CREATED); }
The above example gets the value of the MyRequestHeader
request header, and reads the
body as a byte array. It adds the MyResponseHeader
to the response, writes Hello
World
to the response stream, and sets the response status code to 201 (Created).
As with @RequestBody
and @ResponseBody
, Spring uses HttpMessageConverter
to
convert from and to the request and response streams. For more information on these
converters, see the previous section and Message Converters.
The @ModelAttribute
annotation can be used on methods or on method arguments. This
section explains its usage on methods while the next section explains its usage on
method arguments.
An @ModelAttribute
on a method indicates the purpose of that method is to add one or
more model attributes. Such methods support the same argument types as @RequestMapping
methods but cannot be mapped directly to requests. Instead @ModelAttribute
methods in
a controller are invoked before @RequestMapping
methods, within the same controller. A
couple of examples:
// Add one attribute // The return value of the method is added to the model under the name "account" // You can customize the name via @ModelAttribute("myAccount") @ModelAttribute public Account addAccount(@RequestParam String number) { return accountManager.findAccount(number); } // Add multiple attributes @ModelAttribute public void populateModel(@RequestParam String number, Model model) { model.addAttribute(accountManager.findAccount(number)); // add more ... }
@ModelAttribute
methods are used to populate the model with commonly needed attributes
for example to fill a drop-down with states or with pet types, or to retrieve a command
object like Account in order to use it to represent the data on an HTML form. The latter
case is further discussed in the next section.
Note the two styles of @ModelAttribute
methods. In the first, the method adds an
attribute implicitly by returning it. In the second, the method accepts a Model
and
adds any number of model attributes to it. You can choose between the two styles
depending on your needs.
A controller can have any number of @ModelAttribute
methods. All such methods are
invoked before @RequestMapping
methods of the same controller.
@ModelAttribute
methods can also be defined in an @ControllerAdvice-annotated class
and such methods apply to many controllers. See the the section called “Advising controllers with @ControllerAdvice” section
for more details.
Tip | |
---|---|
What happens when a model attribute name is not explicitly specified? In such cases a
default name is assigned to the model attribute based on its type. For example if the
method returns an object of type |
The @ModelAttribute
annotation can be used on @RequestMapping
methods as well. In
that case the return value of the @RequestMapping
method is interpreted as a model
attribute rather than as a view name. The view name is derived from view name
conventions instead much like for methods returning void — see Section 21.13.3, “The View - RequestToViewNameTranslator”.
As explained in the previous section @ModelAttribute
can be used on methods or on
method arguments. This section explains its usage on method arguments.
An @ModelAttribute
on a method argument indicates the argument should be retrieved
from the model. If not present in the model, the argument should be instantiated first
and then added to the model. Once present in the model, the argument’s fields should be
populated from all request parameters that have matching names. This is known as data
binding in Spring MVC, a very useful mechanism that saves you from having to parse each
form field individually.
@RequestMapping(path = "/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute Pet pet) { }
Given the above example where can the Pet instance come from? There are several options:
@SessionAttributes
— see
the section called “Using @SessionAttributes to store model attributes in the HTTP session between requests”.
@ModelAttribute
method in the same
controller — as explained in the previous section.
An @ModelAttribute
method is a common way to to retrieve an attribute from the
database, which may optionally be stored between requests through the use of
@SessionAttributes
. In some cases it may be convenient to retrieve the attribute by
using an URI template variable and a type converter. Here is an example:
@RequestMapping(path = "/accounts/{account}", method = RequestMethod.PUT) public String save(@ModelAttribute("account") Account account) { }
In this example the name of the model attribute (i.e. "account") matches the name of a
URI template variable. If you register Converter<String, Account>
that can turn the
String
account value into an Account
instance, then the above example will work
without the need for an @ModelAttribute
method.
The next step is data binding. The WebDataBinder
class matches request parameter names — including query string parameters and form fields — to model attribute fields by
name. Matching fields are populated after type conversion (from String to the target
field type) has been applied where necessary. Data binding and validation are covered in
Chapter 8, Validation, Data Binding, and Type Conversion. Customizing the data binding process for a controller level is covered
in the section called “Customizing WebDataBinder initialization”.
As a result of data binding there may be errors such as missing required fields or type
conversion errors. To check for such errors add a BindingResult
argument immediately
following the @ModelAttribute
argument:
@RequestMapping(path = "/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { if (result.hasErrors()) { return "petForm"; } // ... }
With a BindingResult
you can check if errors were found in which case it’s common to
render the same form where the errors can be shown with the help of Spring’s <errors>
form tag.
In addition to data binding you can also invoke validation using your own custom
validator passing the same BindingResult
that was used to record data binding errors.
That allows for data binding and validation errors to be accumulated in one place and
subsequently reported back to the user:
@RequestMapping(path = "/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { new PetValidator().validate(pet, result); if (result.hasErrors()) { return "petForm"; } // ... }
Or you can have validation invoked automatically by adding the JSR-303 @Valid
annotation:
@RequestMapping(path = "/owners/{ownerId}/pets/{petId}/edit", method = RequestMethod.POST) public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { if (result.hasErrors()) { return "petForm"; } // ... }
See Section 8.8, “Spring Validation” and Chapter 8, Validation, Data Binding, and Type Conversion for details on how to configure and use validation.
The type-level @SessionAttributes
annotation declares session attributes used by a
specific handler. This will typically list the names of model attributes or types of
model attributes which should be transparently stored in the session or some
conversational storage, serving as form-backing beans between subsequent requests.
The following code snippet shows the usage of this annotation, specifying the model attribute name:
@Controller @RequestMapping("/editPet.do") @SessionAttributes("pet") public class EditPetForm { // ... }
The previous sections covered use of @ModelAttribute
to support form submission
requests from browser clients. The same annotation is recommended for use with requests
from non-browser clients as well. However there is one notable difference when it comes
to working with HTTP PUT requests. Browsers can submit form data via HTTP GET or HTTP
POST. Non-browser clients can also submit forms via HTTP PUT. This presents a challenge
because the Servlet specification requires the ServletRequest.getParameter*()
family
of methods to support form field access only for HTTP POST, not for HTTP PUT.
To support HTTP PUT and PATCH requests, the spring-web
module provides the filter
HttpPutFormContentFilter
, which can be configured in web.xml
:
<filter> <filter-name>httpPutFormFilter</filter-name> <filter-class>org.springframework.web.filter.HttpPutFormContentFilter</filter-class> </filter> <filter-mapping> <filter-name>httpPutFormFilter</filter-name> <servlet-name>dispatcherServlet</servlet-name> </filter-mapping> <servlet> <servlet-name>dispatcherServlet</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> </servlet>
The above filter intercepts HTTP PUT and PATCH requests with content type
application/x-www-form-urlencoded
, reads the form data from the body of the request,
and wraps the ServletRequest
in order to make the form data available through the
ServletRequest.getParameter*()
family of methods.
Note | |
---|---|
As |
The @CookieValue
annotation allows a method parameter to be bound to the value of an
HTTP cookie.
Let us consider that the following cookie has been received with an http request:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
The following code sample demonstrates how to get the value of the JSESSIONID
cookie:
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) { //... }
Type conversion is applied automatically if the target method parameter type is not
String
. See the section called “Method Parameters And Type Conversion”.
This annotation is supported for annotated handler methods in Servlet and Portlet environments.
The @RequestHeader
annotation allows a method parameter to be bound to a request header.
Here is a sample request header:
Host localhost:8080 Accept text/html,application/xhtml+xml,application/xml;q=0.9 Accept-Language fr,en-gb;q=0.7,en;q=0.3 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 300
The following code sample demonstrates how to get the value of the Accept-Encoding
and
Keep-Alive
headers:
@RequestMapping("/displayHeaderInfo.do") public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding, @RequestHeader("Keep-Alive") long keepAlive) { //... }
Type conversion is applied automatically if the method parameter is not String
. See
the section called “Method Parameters And Type Conversion”.
When an @RequestHeader
annotation is used on a Map<String, String>
,
MultiValueMap<String, String>
, or HttpHeaders
argument, the map is populated
with all header values.
Tip | |
---|---|
Built-in support is available for converting a comma-separated string into an
array/collection of strings or other types known to the type conversion system. For
example a method parameter annotated with |
This annotation is supported for annotated handler methods in Servlet and Portlet environments.
String-based values extracted from the request including request parameters, path
variables, request headers, and cookie values may need to be converted to the target
type of the method parameter or field (e.g., binding a request parameter to a field in
an @ModelAttribute
parameter) they’re bound to. If the target type is not String
,
Spring automatically converts to the appropriate type. All simple types such as int,
long, Date, etc. are supported. You can further customize the conversion process through
a WebDataBinder
(see the section called “Customizing WebDataBinder initialization”) or by registering Formatters
with
the FormattingConversionService
(see Section 8.6, “Spring Field Formatting”).
To customize request parameter binding with PropertyEditors through Spring’s
WebDataBinder
, you can use @InitBinder
-annotated methods within your controller,
@InitBinder
methods within an @ControllerAdvice
class, or provide a custom
WebBindingInitializer
. See the the section called “Advising controllers with @ControllerAdvice” section for more details.
Annotating controller methods with @InitBinder
allows you to configure web data
binding directly within your controller class. @InitBinder
identifies methods that
initialize the WebDataBinder
that will be used to populate command and form object
arguments of annotated handler methods.
Such init-binder methods support all arguments that @RequestMapping
supports, except
for command/form objects and corresponding validation result objects. Init-binder
methods must not have a return value. Thus, they are usually declared as void
.
Typical arguments include WebDataBinder
in combination with WebRequest
or
java.util.Locale
, allowing code to register context-specific editors.
The following example demonstrates the use of @InitBinder
to configure a
CustomDateEditor
for all java.util.Date
form properties.
@Controller public class MyFormController { @InitBinder public void initBinder(WebDataBinder binder) { SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd"); dateFormat.setLenient(false); binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false)); } // ... }
Alternatively, as of Spring 4.2, consider using addCustomFormatter
to specify
Formatter
implementations instead of PropertyEditor
instances. This is
particularly useful if you happen to have a Formatter
-based setup in a shared
FormattingConversionService
as well, with the same approach to be reused for
controller-specific tweaking of the binding rules.
@Controller public class MyFormController { @InitBinder public void initBinder(WebDataBinder binder) { binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd")); } // ... }
To externalize data binding initialization, you can provide a custom implementation of
the WebBindingInitializer
interface, which you then enable by supplying a custom bean
configuration for an AnnotationMethodHandlerAdapter
, thus overriding the default
configuration.
The following example from the PetClinic application shows a configuration using a
custom implementation of the WebBindingInitializer
interface,
org.springframework.samples.petclinic.web.ClinicBindingInitializer
, which configures
PropertyEditors required by several of the PetClinic controllers.
<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter"> <property name="cacheSeconds" value="0" /> <property name="webBindingInitializer"> <bean class="org.springframework.samples.petclinic.web.ClinicBindingInitializer" /> </property> </bean>
@InitBinder
methods can also be defined in an @ControllerAdvice-annotated class in
which case they apply to matching controllers. This provides an alternative to using a
WebBindingInitializer
. See the the section called “Advising controllers with @ControllerAdvice” section for more details.
The @ControllerAdvice
annotation is a component annotation allowing implementation
classes to be auto-detected through classpath scanning. It is automatically enabled when
using the MVC namespace or the MVC Java config.
Classes annotated with @ControllerAdvice
can contain @ExceptionHandler
,
@InitBinder
, and @ModelAttribute
annotated methods, and these methods will apply to
@RequestMapping
methods across all controller hierarchies as opposed to the controller
hierarchy within which they are declared.
The @ControllerAdvice
annotation can also target a subset of controllers with its
attributes:
// Target all Controllers annotated with @RestController @ControllerAdvice(annotations = RestController.class) public class AnnotationAdvice {} // Target all Controllers within specific packages @ControllerAdvice("org.example.controllers") public class BasePackageAdvice {} // Target all Controllers assignable to specific classes @ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class}) public class AssignableTypesAdvice {}
Check out the
@ControllerAdvice
documentation for more details.
It can sometimes be useful to filter contextually the object that will be serialized to the HTTP response body. In order to provide such capability, Spring MVC has built-in support for rendering with Jackson’s Serialization Views.
To use it with an @ResponseBody
controller method or controller methods that return
ResponseEntity
, simply add the @JsonView
annotation with a class argument specifying
the view class or interface to be used:
@RestController public class UserController { @RequestMapping(path = "/user", method = RequestMethod.GET) @JsonView(User.WithoutPasswordView.class) public User getUser() { return new User("eric", "7!jd#h23"); } } public class User { public interface WithoutPasswordView {}; public interface WithPasswordView extends WithoutPasswordView {}; private String username; private String password; public User() { } public User(String username, String password) { this.username = username; this.password = password; } @JsonView(WithoutPasswordView.class) public String getUsername() { return this.username; } @JsonView(WithPasswordView.class) public String getPassword() { return this.password; } }
Note | |
---|---|
Note that despite |
For controllers relying on view resolution, simply add the serialization view class to the model:
@Controller public class UserController extends AbstractController { @RequestMapping(path = "/user", method = RequestMethod.GET) public String getUser(Model model) { model.addAttribute("user", new User("eric", "7!jd#h23")); model.addAttribute(JsonView.class.getName(), User.WithoutPasswordView.class); return "userView"; } }
In order to enable JSONP support for @ResponseBody
and ResponseEntity
methods, declare an @ControllerAdvice
bean that extends
AbstractJsonpResponseBodyAdvice
as shown below where the constructor argument indicates
the JSONP query parameter name(s):
@ControllerAdvice public class JsonpAdvice extends AbstractJsonpResponseBodyAdvice { public JsonpAdvice() { super("callback"); } }
For controllers relying on view resolution, JSONP is automatically enabled when the
request has a query parameter named jsonp
or callback
. Those names can be
customized through jsonpParameterNames
property.
Spring MVC 3.2 introduced Servlet 3 based asynchronous request processing. Instead of
returning a value, as usual, a controller method can now return a
java.util.concurrent.Callable
and produce the return value from a Spring MVC managed thread.
Meanwhile the main Servlet container thread is exited and released and allowed to process other
requests. Spring MVC invokes the Callable
in a separate thread with the help of a
TaskExecutor
and when the Callable
returns, the request is dispatched back to the
Servlet container to resume processing using the value returned by the Callable
. Here
is an example of such a controller method:
@RequestMapping(method=RequestMethod.POST) public Callable<String> processUpload(final MultipartFile file) { return new Callable<String>() { public String call() throws Exception { // ... return "someView"; } }; }
Another option is for the controller method to return an instance of DeferredResult
. In this
case the return value will also be produced from any thread, i.e. one that
is not managed by Spring MVC. For example the result may be produced in response to some
external event such as a JMS message, a scheduled task, and so on. Here is an example
of such a controller method:
@RequestMapping("/quotes") @ResponseBody public DeferredResult<String> quotes() { DeferredResult<String> deferredResult = new DeferredResult<String>(); // Save the deferredResult somewhere.. return deferredResult; } // In some other thread... deferredResult.setResult(data);
This may be difficult to understand without any knowledge of the Servlet 3.0 asynchronous request processing features. It would certainly help to read up on that. Here are a few basic facts about the underlying mechanism:
ServletRequest
can be put in asynchronous mode by calling request.startAsync()
.
The main effect of doing so is that the Servlet, as well as any Filters, can exit but
the response will remain open to allow processing to complete later.
request.startAsync()
returns AsyncContext
which can be used for
further control over async processing. For example it provides the method dispatch
,
that is similar to a forward from the Servlet API except it allows an
application to resume request processing on a Servlet container thread.
ServletRequest
provides access to the current DispatcherType
that can
be used to distinguish between processing the initial request, an async
dispatch, a forward, and other dispatcher types.
With the above in mind, the following is the sequence of events for async request
processing with a Callable
:
Callable
.
Callable
to
a TaskExecutor
for processing in a separate thread.
DispatcherServlet
and all Filter’s exit the Servlet container thread
but the response remains open.
Callable
produces a result and Spring MVC dispatches the request back
to the Servlet container to resume processing.
DispatcherServlet
is invoked again and processing resumes with the
asynchronously produced result from the Callable
.
The sequence for DeferredResult
is very similar except it’s up to the
application to produce the asynchronous result from any thread:
DeferredResult
and saves it in some in-memory
queue or list where it can be accessed.
DispatcherServlet
and all configured Filter’s exit the request
processing thread but the response remains open.
DeferredResult
from some thread and Spring MVC
dispatches the request back to the Servlet container.
DispatcherServlet
is invoked again and processing resumes with the
asynchronously produced result.
For further background on the motivation for async request processing and when or why to use it please read this blog post series.
What happens if a Callable
returned from a controller method raises an
Exception while being executed? The short answer is the same as what happens
when a controller method raises an exception. It goes through the regular
exception handling mechanism. The longer explanation is that when a Callable
raises an Exception Spring MVC dispatches to the Servlet container with
the Exception
as the result and that leads to resume request processing
with the Exception
instead of a controller method return value.
When using a DeferredResult
you have a choice whether to call
setResult
or setErrorResult
with an Exception
instance.
A HandlerInterceptor
can also implement AsyncHandlerInterceptor
in order
to implement the afterConcurrentHandlingStarted
callback, which is called
instead of postHandle
and afterCompletion
when asynchronous processing
starts.
A HandlerInterceptor
can also register a CallableProcessingInterceptor
or a DeferredResultProcessingInterceptor
in order to integrate more
deeply with the lifecycle of an asynchronous request and for example
handle a timeout event. See the Javadoc of AsyncHandlerInterceptor
for more details.
The DeferredResult
type also provides methods such as onTimeout(Runnable)
and onCompletion(Runnable)
. See the Javadoc of DeferredResult
for more
details.
When using a Callable
you can wrap it with an instance of WebAsyncTask
which also provides registration methods for timeout and completion.
A controller method can use DeferredResult
and Callable
to produce its
return value asynchronously and that can be used to implement techniques such as
long polling
where the server can push an event to the client as soon as possible.
What if you wanted to push multiple events on a single HTTP response?
This is a technique related to "Long Polling" that is known as "HTTP Streaming".
Spring MVC makes this possible through the ResponseBodyEmitter
return value
type which can be used to send multiple Objects, instead of one as is normally
the case with @ResponseBody
, where each Object sent is written to the
response with an HttpMessageConverter
.
Here is an example of that:
@RequestMapping("/events") public ResponseBodyEmitter<String> handle() { ResponseBodyEmitter<String> emitter = new ResponseBodyEmitter<String>(); // Save the emitter somewhere.. return emitter; } // In some other thread emitter.send("Hello once"); // and again later on emitter.send("Hello again"); // and done at some point emitter.complete();
Note that ResponseBodyEmitter
can also be used as the body in a
ResponseEntity
in order to customize the status and headers of
the response.
SseEmitter
is a sub-class of ResponseBodyEmitter
providing support for
Server-Sent Events.
Server-sent events is a just another variation on the same "HTTP Streaming"
technique except events pushed from the server are formatted according to
the W3C Servet-Sent Events specification.
Server-Sent Events can be used for their intended purpose, that is to push
events from the server to clients. It is quite easy to do in Spring MVC and
requires simply returning a value of type SseEmitter
.
Note however that Internet Explorer does not support Server-Sent Events and that for more advanced web application messaging scenarios such as online games, collaboration, financial applicatinos, and others it’s better to consider Spring’s WebSocket support that includes SockJS-style WebSocket emulation falling back to a very wide range of browsers (including Internet Explorer) and also higher-level messaging patterns for interacting with clients through a publish-subscribe model within a more messaging-centric architecture. For further background on this see the following blog post.
ResponseBodyEmitter
allows sending events by writing Objects to the
response through an HttpMessageConverter
. This is probably the most common
case, for example when writing JSON data. However sometimes it is useful to
bypass message conversion and write directly to the response OutputStream
for example for a file download. This can be done with the help of the
StreamingResponseBody
return value type.
Here is an example of that:
@RequestMapping("/download") public StreamingResponseBody handle() { return new StreamingResponseBody() { @Override public void writeTo(OutputStream outputStream) throws IOException { // write... } }; }
Note that StreamingResponseBody
can also be used as the body in a
ResponseEntity
in order to customize the status and headers of
the response.
For applications configured with a web.xml
be sure to update to version 3.0:
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> ... </web-app>
Asynchronous support must be enabled on the DispatcherServlet
through the
<async-supported>true</async-supported>
web.xml sub-element. Additionally
any Filter
that participates in asyncrequest processing must be configured
to support the ASYNC dispatcher type. It should be safe to enable the ASYNC
dispatcher type for all filters provided with the Spring Framework since they
usually extend OncePerRequestFilter
and that has runtime checks for whether
the filter needs to be involved in async dispatches or not.
Below is some example web.xml configuration:
<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"> <filter> <filter-name>Spring OpenEntityManagerInViewFilter</filter-name> <filter-class>org.springframework.~.OpenEntityManagerInViewFilter</filter-class> <async-supported>true</async-supported> </filter> <filter-mapping> <filter-name>Spring OpenEntityManagerInViewFilter</filter-name> <url-pattern>/*</url-pattern> <dispatcher>REQUEST</dispatcher> <dispatcher>ASYNC</dispatcher> </filter-mapping> </web-app>
If using Servlet 3, Java based configuration for example via WebApplicationInitializer
,
you’ll also need to set the "asyncSupported" flag as well as the ASYNC dispatcher type
just like with web.xml
. To simplify all this configuration, consider extending
AbstractDispatcherServletInitializer
or
AbstractAnnotationConfigDispatcherServletInitializer
which automatically
set those options and make it very easy to register Filter
instances.
The MVC Java config and the MVC namespace provide options for configuring
asynchronous request processing. WebMvcConfigurer
has the method
configureAsyncSupport
while <mvc:annotation-driven>
has an
<async-support>
sub-element.
Those allow you to configure the default timeout value to use for async requests, which
if not set depends on the underlying Servlet container (e.g. 10 seconds on Tomcat). You
can also configure an AsyncTaskExecutor
to use for executing Callable
instances
returned from controller methods. It is highly recommended to configure this property
since by default Spring MVC uses SimpleAsyncTaskExecutor
. The MVC Java config and the
MVC namespace also allow you to register CallableProcessingInterceptor
and
DeferredResultProcessingInterceptor
instances.
If you need to override the default timeout value for a specific DeferredResult
, you
can do so by using the appropriate class constructor. Similarly, for a Callable
, you
can wrap it in a WebAsyncTask
and use the appropriate class constructor to customize
the timeout value. The class constructor of WebAsyncTask
also allows providing an
AsyncTaskExecutor
.
The spring-test
module offers first class support for testing annotated controllers.
See Section 14.6, “Spring MVC Test Framework”.
In previous versions of Spring, users were required to define one or more
HandlerMapping
beans in the web application context to map incoming web requests to
appropriate handlers. With the introduction of annotated controllers, you generally
don’t need to do that because the RequestMappingHandlerMapping
automatically looks for
@RequestMapping
annotations on all @Controller
beans. However, do keep in mind that
all HandlerMapping
classes extending from AbstractHandlerMapping
have the following
properties that you can use to customize their behavior:
interceptors
List of interceptors to use. HandlerInterceptors are discussed in
Section 21.4.1, “Intercepting requests with a HandlerInterceptor”.
defaultHandler
Default handler to use, when this handler mapping does not result in
a matching handler.
order
Based on the value of the order property (see the
org.springframework.core.Ordered
interface), Spring sorts all handler mappings
available in the context and applies the first matching handler.
alwaysUseFullPath
If true
, Spring uses the full path within the current Servlet
context to find an appropriate handler. If false
(the default), the path within the
current Servlet mapping is used. For example, if a Servlet is mapped using
/testing/*
and the alwaysUseFullPath
property is set to true,
/testing/viewPage.html
is used, whereas if the property is set to false,
/viewPage.html
is used.
urlDecode
Defaults to true
, as of Spring 2.5. If you prefer to compare encoded
paths, set this flag to false
. However, the HttpServletRequest
always exposes the
Servlet path in decoded form. Be aware that the Servlet path will not match when
compared with encoded paths.
The following example shows how to configure an interceptor:
<beans> <bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"> <property name="interceptors"> <bean class="example.MyInterceptor"/> </property> </bean> <beans>
Spring’s handler mapping mechanism includes handler interceptors, which are useful when you want to apply specific functionality to certain requests, for example, checking for a principal.
Interceptors located in the handler mapping must implement HandlerInterceptor
from the
org.springframework.web.servlet
package. This interface defines three methods:
preHandle(..)
is called before the actual handler is executed; postHandle(..)
is
called after the handler is executed; and afterCompletion(..)
is called after
the complete request has finished. These three methods should provide enough
flexibility to do all kinds of preprocessing and postprocessing.
The preHandle(..)
method returns a boolean value. You can use this method to break or
continue the processing of the execution chain. When this method returns true
, the
handler execution chain will continue; when it returns false, the DispatcherServlet
assumes the interceptor itself has taken care of requests (and, for example, rendered an
appropriate view) and does not continue executing the other interceptors and the actual
handler in the execution chain.
Interceptors can be configured using the interceptors
property, which is present on
all HandlerMapping
classes extending from AbstractHandlerMapping
. This is shown in
the example below:
<beans> <bean id="handlerMapping" class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerMapping"> <property name="interceptors"> <list> <ref bean="officeHoursInterceptor"/> </list> </property> </bean> <bean id="officeHoursInterceptor" class="samples.TimeBasedAccessInterceptor"> <property name="openingTime" value="9"/> <property name="closingTime" value="18"/> </bean> <beans>
package samples; public class TimeBasedAccessInterceptor extends HandlerInterceptorAdapter { private int openingTime; private int closingTime; public void setOpeningTime(int openingTime) { this.openingTime = openingTime; } public void setClosingTime(int closingTime) { this.closingTime = closingTime; } public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { Calendar cal = Calendar.getInstance(); int hour = cal.get(HOUR_OF_DAY); if (openingTime <= hour && hour < closingTime) { return true; } response.sendRedirect("http://host.com/outsideOfficeHours.html"); return false; } }
Any request handled by this mapping is intercepted by the TimeBasedAccessInterceptor
.
If the current time is outside office hours, the user is redirected to a static HTML
file that says, for example, you can only access the website during office hours.
Note | |
---|---|
When using the |
As you can see, the Spring adapter class HandlerInterceptorAdapter
makes it easier to
extend the HandlerInterceptor
interface.
Tip | |
---|---|
In the example above, the configured interceptor will apply to all requests handled with
annotated controller methods. If you want to narrow down the URL paths to which an
interceptor applies, you can use the MVC namespace or the MVC Java config, or declare
bean instances of type |
Note that the postHandle
method of HandlerInterceptor
is not always ideally suited for
use with @ResponseBody
and ResponseEntity
methods. In such cases an HttpMessageConverter
writes to and commits the response before postHandle
is called which makes it impossible
to change the response, for example to add a header. Instead an application can implement
ResponseBodyAdvice
and either declare it as an @ControllerAdvice
bean or configure it
directly on RequestMappingHandlerAdapter
.
All MVC frameworks for web applications provide a way to address views. Spring provides view resolvers, which enable you to render models in a browser without tying you to a specific view technology. Out of the box, Spring enables you to use JSPs, Velocity templates and XSLT views, for example. See Chapter 22, View technologies for a discussion of how to integrate and use a number of disparate view technologies.
The two interfaces that are important to the way Spring handles views are ViewResolver
and View
. The ViewResolver
provides a mapping between view names and actual views.
The View
interface addresses the preparation of the request and hands the request over
to one of the view technologies.
As discussed in Section 21.3, “Implementing Controllers”, all handler methods in the Spring Web MVC
controllers must resolve to a logical view name, either explicitly (e.g., by returning a
String
, View
, or ModelAndView
) or implicitly (i.e., based on conventions). Views
in Spring are addressed by a logical view name and are resolved by a view resolver.
Spring comes with quite a few view resolvers. This table lists most of them; a couple of
examples follow.
Table 21.3. View resolvers
ViewResolver | Description |
---|---|
| Abstract view resolver that caches views. Often views need preparation before they can be used; extending this view resolver provides caching. |
| Implementation of |
| Implementation of |
| Simple implementation of the |
| Convenient subclass of |
| Convenient subclass of |
| Implementation of the |
As an example, with JSP as a view technology, you can use the UrlBasedViewResolver
.
This view resolver translates a view name to a URL and hands the request over to the
RequestDispatcher to render the view.
<bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean>
When returning test
as a logical view name, this view resolver forwards the request to
the RequestDispatcher
that will send the request to /WEB-INF/jsp/test.jsp
.
When you combine different view technologies in a web application, you can use the
ResourceBundleViewResolver
:
<bean id="viewResolver" class="org.springframework.web.servlet.view.ResourceBundleViewResolver"> <property name="basename" value="views"/> <property name="defaultParentView" value="parentView"/> </bean>
The ResourceBundleViewResolver
inspects the ResourceBundle
identified by the
basename, and for each view it is supposed to resolve, it uses the value of the property
[viewname].(class)
as the view class and the value of the property [viewname].url
as
the view url. Examples can be found in the next chapter which covers view technologies.
As you can see, you can identify a parent view, from which all views in the properties
file "extend". This way you can specify a default view class, for example.
Note | |
---|---|
Subclasses of |
Spring supports multiple view resolvers. Thus you can chain resolvers and, for example,
override specific views in certain circumstances. You chain view resolvers by adding
more than one resolver to your application context and, if necessary, by setting the
order
property to specify ordering. Remember, the higher the order property, the later
the view resolver is positioned in the chain.
In the following example, the chain of view resolvers consists of two resolvers, an
InternalResourceViewResolver
, which is always automatically positioned as the last
resolver in the chain, and an XmlViewResolver
for specifying Excel views. Excel views
are not supported by the InternalResourceViewResolver
.
<bean id="jspViewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> <bean id="excelViewResolver" class="org.springframework.web.servlet.view.XmlViewResolver"> <property name="order" value="1"/> <property name="location" value="/WEB-INF/views.xml"/> </bean> <!-- in views.xml --> <beans> <bean name="report" class="org.springframework.example.ReportExcelView"/> </beans>
If a specific view resolver does not result in a view, Spring examines the context for
other view resolvers. If additional view resolvers exist, Spring continues to inspect
them until a view is resolved. If no view resolver returns a view, Spring throws a
ServletException
.
The contract of a view resolver specifies that a view resolver can return null to
indicate the view could not be found. Not all view resolvers do this, however, because
in some cases, the resolver simply cannot detect whether or not the view exists. For
example, the InternalResourceViewResolver
uses the RequestDispatcher
internally, and
dispatching is the only way to figure out if a JSP exists, but this action can only
execute once. The same holds for the VelocityViewResolver
and some others. Check the
javadocs of the specific view resolver to see whether it reports non-existing views.
Thus, putting an InternalResourceViewResolver
in the chain in a place other than
the last results in the chain not being fully inspected, because the
InternalResourceViewResolver
will always return a view!
As mentioned previously, a controller typically returns a logical view name, which a
view resolver resolves to a particular view technology. For view technologies such as
JSPs that are processed through the Servlet or JSP engine, this resolution is usually
handled through the combination of InternalResourceViewResolver
and
InternalResourceView
, which issues an internal forward or include via the Servlet
API’s RequestDispatcher.forward(..)
method or RequestDispatcher.include()
method.
For other view technologies, such as Velocity, XSLT, and so on, the view itself writes
the content directly to the response stream.
It is sometimes desirable to issue an HTTP redirect back to the client, before the view
is rendered. This is desirable, for example, when one controller has been called with
POST
data, and the response is actually a delegation to another controller (for
example on a successful form submission). In this case, a normal internal forward will
mean that the other controller will also see the same POST
data, which is potentially
problematic if it can confuse it with other expected data. Another reason to perform a
redirect before displaying the result is to eliminate the possibility of the user
submitting the form data multiple times. In this scenario, the browser will first send
an initial POST
; it will then receive a response to redirect to a different URL; and
finally the browser will perform a subsequent GET
for the URL named in the redirect
response. Thus, from the perspective of the browser, the current page does not reflect
the result of a POST
but rather of a GET
. The end effect is that there is no way the
user can accidentally re- POST
the same data by performing a refresh. The refresh
forces a GET
of the result page, not a resend of the initial POST
data.
One way to force a redirect as the result of a controller response is for the controller
to create and return an instance of Spring’s RedirectView
. In this case,
DispatcherServlet
does not use the normal view resolution mechanism. Rather because it
has been given the (redirect) view already, the DispatcherServlet
simply instructs the
view to do its work. The RedirectView
in turn calls HttpServletResponse.sendRedirect()
to send an HTTP redirect to the client browser.
If you use RedirectView
and the view is created by the controller itself, it is
recommended that you configure the redirect URL to be injected into the controller so
that it is not baked into the controller but configured in the context along with the
view names. The the section called “The redirect: prefix” facilitates this decoupling.
By default all model attributes are considered to be exposed as URI template variables in the redirect URL. Of the remaining attributes those that are primitive types or collections/arrays of primitive types are automatically appended as query parameters.
Appending primitive type attributes as query parameters may be the desired result if a
model instance was prepared specifically for the redirect. However, in annotated
controllers the model may contain additional attributes added for rendering purposes (e.g.
drop-down field values). To avoid the possibility of having such attributes appear in the
URL, an @RequestMapping
method can declare an argument of type RedirectAttributes
and
use it to specify the exact attributes to make available to RedirectView
. If the method
does redirect, the content of RedirectAttributes
is used. Otherwise the content of the
model is used.
The RequestMappingHandlerAdapter
provides a flag called
"ignoreDefaultModelOnRedirect"
that can be used to indicate the content of the default
Model
should never be used if a controller method redirects. Instead the controller
method should declare an attribute of type RedirectAttributes
or if it doesn’t do so
no attributes should be passed on to RedirectView
. Both the MVC namespace and the MVC
Java config keep this flag set to false
in order to maintain backwards compatibility.
However, for new applications we recommend setting it to true
Note that URI template variables from the present request are automatically made
available when expanding a redirect URL and do not need to be added explicitly neither
through Model
nor RedirectAttributes
. For example:
@RequestMapping(path = "/files/{path}", method = RequestMethod.POST) public String upload(...) { // ... return "redirect:files/{path}"; }
Another way of passing data to the redirect target is via Flash Attributes. Unlike other redirect attributes, flash attributes are saved in the HTTP session (and hence do not appear in the URL). See Section 21.6, “Using flash attributes” for more information.
While the use of RedirectView
works fine, if the controller itself creates the
RedirectView
, there is no avoiding the fact that the controller is aware that a
redirection is happening. This is really suboptimal and couples things too tightly. The
controller should not really care about how the response gets handled. In general it
should operate only in terms of view names that have been injected into it.
The special redirect:
prefix allows you to accomplish this. If a view name is returned
that has the prefix redirect:
, the UrlBasedViewResolver
(and all subclasses) will
recognize this as a special indication that a redirect is needed. The rest of the view
name will be treated as the redirect URL.
The net effect is the same as if the controller had returned a RedirectView
, but now
the controller itself can simply operate in terms of logical view names. A logical view
name such as redirect:/myapp/some/resource
will redirect relative to the current
Servlet context, while a name such as redirect:http://myhost.com/some/arbitrary/path
will redirect to an absolute URL.
It is also possible to use a special forward:
prefix for view names that are
ultimately resolved by UrlBasedViewResolver
and subclasses. This creates an
InternalResourceView
(which ultimately does a RequestDispatcher.forward()
) around
the rest of the view name, which is considered a URL. Therefore, this prefix is not
useful with InternalResourceViewResolver
and InternalResourceView
(for JSPs for
example). But the prefix can be helpful when you are primarily using another view
technology, but still want to force a forward of a resource to be handled by the
Servlet/JSP engine. (Note that you may also chain multiple view resolvers, instead.)
As with the redirect:
prefix, if the view name with the forward:
prefix is injected
into the controller, the controller does not detect that anything special is happening
in terms of handling the response.
The ContentNegotiatingViewResolver
does not resolve views itself but rather delegates
to other view resolvers, selecting the view that resembles the representation requested
by the client. Two strategies exist for a client to request a representation from the
server:
http://www.example.com/users/fred.pdf
requests a PDF
representation of the user fred, and http://www.example.com/users/fred.xml
requests
an XML representation.
Accept
HTTP
request header to list the media
types that it understands. For example, an HTTP request for
http://www.example.com/users/fred
with an Accept
header set to application/pdf
requests a PDF representation of the user fred, while
http://www.example.com/users/fred
with an Accept
header set to text/xml
requests
an XML representation. This strategy is known as
content negotiation.
Note | |
---|---|
One issue with the Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8 For this reason it is common to see the use of a distinct URI for each representation when developing browser based web applications. |
To support multiple representations of a resource, Spring provides the
ContentNegotiatingViewResolver
to resolve a view based on the file extension or
Accept
header of the HTTP request. ContentNegotiatingViewResolver
does not perform
the view resolution itself but instead delegates to a list of view resolvers that you
specify through the bean property ViewResolvers
.
The ContentNegotiatingViewResolver
selects an appropriate View
to handle the request
by comparing the request media type(s) with the media type (also known as
Content-Type
) supported by the View
associated with each of its ViewResolvers
. The
first View
in the list that has a compatible Content-Type
returns the representation
to the client. If a compatible view cannot be supplied by the ViewResolver
chain, then
the list of views specified through the DefaultViews
property will be consulted. This
latter option is appropriate for singleton Views
that can render an appropriate
representation of the current resource regardless of the logical view name. The Accept
header may include wild cards, for example text/*
, in which case a View
whose
Content-Type was text/xml
is a compatible match.
To support the resolution of a view based on a file extension, use the
ContentNegotiatingViewResolver
bean property mediaTypes
to specify a mapping of file
extensions to media types. For more information on the algorithm used to determine the
request media type, refer to the API documentation for ContentNegotiatingViewResolver
.
Here is an example configuration of a ContentNegotiatingViewResolver:
<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver"> <property name="mediaTypes"> <map> <entry key="atom" value="application/atom+xml"/> <entry key="html" value="text/html"/> <entry key="json" value="application/json"/> </map> </property> <property name="viewResolvers"> <list> <bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/> <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </list> </property> <property name="defaultViews"> <list> <bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView" /> </list> </property> </bean> <bean id="content" class="com.foo.samples.rest.SampleContentAtomView"/>
The InternalResourceViewResolver
handles the translation of view names and JSP pages,
while the BeanNameViewResolver
returns a view based on the name of a bean. (See
"Resolving views with the ViewResolver interface" for more
details on how Spring looks up and instantiates a view.) In this example, the content
bean is a class that inherits from AbstractAtomFeedView
, which returns an Atom RSS
feed. For more information on creating an Atom Feed representation, see the section Atom
Views.
In the above configuration, if a request is made with an .html
extension, the view
resolver looks for a view that matches the text/html
media type. The
InternalResourceViewResolver
provides the matching view for text/html
. If the
request is made with the file extension .atom
, the view resolver looks for a view that
matches the application/atom+xml
media type. This view is provided by the
BeanNameViewResolver
that maps to the SampleContentAtomView
if the view name
returned is content
. If the request is made with the file extension .json
, the
MappingJackson2JsonView
instance from the DefaultViews
list will be selected
regardless of the view name. Alternatively, client requests can be made without a file
extension but with the Accept
header set to the preferred media-type, and the same
resolution of request to views would occur.
Note | |
---|---|
If `ContentNegotiatingViewResolver’s list of ViewResolvers is not configured explicitly, it automatically uses any ViewResolvers defined in the application context. |
The corresponding controller code that returns an Atom RSS feed for a URI of the form
http://localhost/content.atom
or http://localhost/content
with an Accept
header of
application/atom+xml is shown below.
@Controller public class ContentController { private List<SampleContent> contentList = new ArrayList<SampleContent>(); @RequestMapping(path="/content", method=RequestMethod.GET) public ModelAndView getContent() { ModelAndView mav = new ModelAndView(); mav.setViewName("content"); mav.addObject("sampleContentList", contentList); return mav; } }
Flash attributes provide a way for one request to store attributes intended for use in another. This is most commonly needed when redirecting — for example, the Post/Redirect/Get pattern. Flash attributes are saved temporarily before the redirect (typically in the session) to be made available to the request after the redirect and removed immediately.
Spring MVC has two main abstractions in support of flash attributes. FlashMap
is used
to hold flash attributes while FlashMapManager
is used to store, retrieve, and manage
FlashMap
instances.
Flash attribute support is always "on" and does not need to enabled explicitly although
if not used, it never causes HTTP session creation. On each request there is an "input"
FlashMap
with attributes passed from a previous request (if any) and an "output"
FlashMap
with attributes to save for a subsequent request. Both FlashMap
instances
are accessible from anywhere in Spring MVC through static methods in
RequestContextUtils
.
Annotated controllers typically do not need to work with FlashMap
directly. Instead an
@RequestMapping
method can accept an argument of type RedirectAttributes
and use it
to add flash attributes for a redirect scenario. Flash attributes added via
RedirectAttributes
are automatically propagated to the "output" FlashMap. Similarly,
after the redirect, attributes from the "input" FlashMap
are automatically added to the
Model
of the controller serving the target URL.
Spring MVC provides a mechanism for building and encoding a URI using
UriComponentsBuilder
and UriComponents
.
For example you can expand and encode a URI template string:
UriComponents uriComponents = UriComponentsBuilder.fromUriString( "http://example.com/hotels/{hotel}/bookings/{booking}").build(); URI uri = uriComponents.expand("42", "21").encode().toUri();
Note that UriComponents
is immutable and the expand()
and encode()
operations
return new instances if necessary.
You can also expand and encode using individual URI components:
UriComponents uriComponents = UriComponentsBuilder.newInstance() .scheme("http").host("example.com").path("/hotels/{hotel}/bookings/{booking}").build() .expand("42", "21") .encode();
In a Servlet environment the ServletUriComponentsBuilder
sub-class provides static
factory methods to copy available URL information from a Servlet requests:
HttpServletRequest request = ... // Re-use host, scheme, port, path and query string // Replace the "accountId" query param ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request) .replaceQueryParam("accountId", "{id}").build() .expand("123") .encode();
Alternatively, you may choose to copy a subset of the available information up to and including the context path:
// Re-use host, port and context path // Append "/accounts" to the path ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request) .path("/accounts").build()
Or in cases where the DispatcherServlet
is mapped by name (e.g. /main/*
), you can
also have the literal part of the servlet mapping included:
// Re-use host, port, context path // Append the literal part of the servlet mapping to the path // Append "/accounts" to the path ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request) .path("/accounts").build()
Spring MVC also provides a mechanism for building links to controller methods. For example, given:
@Controller @RequestMapping("/hotels/{hotel}") public class BookingController { @RequestMapping("/bookings/{booking}") public String getBooking(@PathVariable Long booking) { // ... }
You can prepare a link by referring to the method by name:
UriComponents uriComponents = MvcUriComponentsBuilder .fromMethodName(BookingController.class, "getBooking", 21).buildAndExpand(42); URI uri = uriComponents.encode().toUri();
In the above example we provided actual method argument values, in this case the long value 21,
to be used as a path variable and inserted into the URL. Furthermore, we provided the
value 42 in order to fill in any remaining URI variables such as the "hotel" variable inherited
from the type-level request mapping. If the method had more arguments you can supply null for
arguments not needed for the URL. In general only @PathVariable
and @RequestParam
arguments
are relevant for constructing the URL.
There are additional ways to use MvcUriComponentsBuilder
. For example you can use a technique
akin to mock testing through proxies to avoid referring to the controller method by name
(the example assumes static import of MvcUriComponentsBuilder.on
):
UriComponents uriComponents = MvcUriComponentsBuilder .fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42); URI uri = uriComponents.encode().toUri();
The above examples use static methods in MvcUriComponentsBuilder
. Internally they rely
on ServletUriComponentsBuilder
to prepare a base URL from the scheme, host, port,
context path and servlet path of the current request. This works well in most cases,
however sometimes it may be insufficient. For example you may be outside the context of
a request (e.g. a batch process that prepares links) or perhaps you need to insert a path
prefix (e.g. a locale prefix that was removed from the request path and needs to be
re-inserted into links).
For such cases you can use the static "fromXxx" overloaded methods that accept a
UriComponentsBuilder
to use base URL. Or you can create an instance of MvcUriComponentsBuilder
with a base URL and then use the instance-based "withXxx" methods. For example:
UriComponentsBuilder base = ServletUriComponentsBuilder.fromCurrentContextPath().path("/en"); MvcUriComponentsBuilder builder = MvcUriComponentsBuilder.relativeTo(base); builder.withMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42); URI uri = uriComponents.encode().toUri();
You can also build links to annotated controllers from views such as JSP, Thymeleaf,
FreeMarker. This can be done using the fromMappingName
method in MvcUriComponentsBuilder
which refers to mappings by name.
Every @RequestMapping
is assigned a default name based on the capital letters of the
class and the full method name. For example, the method getFoo
in class FooController
is assigned the name "FC#getFoo". This strategy can be replaced or customized by creating
an instance of HandlerMethodMappingNamingStrategy
and plugging it into your
RequestMappingHandlerMapping
. The default strategy implementation also looks at the
name attribute on @RequestMapping
and uses that if present. That means if the default
mapping name assigned conflicts with another (e.g. overloaded methods) you can assign
a name explicitly on the @RequestMapping
.
Note | |
---|---|
The assigned request mapping names are logged at TRACE level on startup. |
The Spring JSP tag library provides a function called mvcUrl
that can be used to
prepare links to controller methods based on this mechanism.
For example given:
@RequestMapping("/people/{id}/addresses") public class PersonAddressController { @RequestMapping("/{country}") public HttpEntity getAddress(@PathVariable String country) { ... } }
You can prepare a link from a JSP as follows:
<%@ taglib uri="http://www.springframework.org/tags" prefix="s" %> ... <a href="${s:mvcUrl(''PAC#getAddress'').arg(0,''US'').buildAndExpand(''123'')}">Get Address</a>
The above example relies on the mvcUrl
JSP function declared in the Spring tag library
(i.e. META-INF/spring.tld). For more advanced cases (e.g. a custom base URL as explained
in the previous section), it is easy to define your own function, or use a custom tag file,
in order to use a specific instance of MvcUriComponentsBuilder
with a custom base URL.
Most parts of Spring’s architecture support internationalization, just as the Spring web
MVC framework does. DispatcherServlet
enables you to automatically resolve messages
using the client’s locale. This is done with LocaleResolver
objects.
When a request comes in, the DispatcherServlet
looks for a locale resolver, and if it
finds one it tries to use it to set the locale. Using the RequestContext.getLocale()
method, you can always retrieve the locale that was resolved by the locale resolver.
In addition to automatic locale resolution, you can also attach an interceptor to the handler mapping (see Section 21.4.1, “Intercepting requests with a HandlerInterceptor” for more information on handler mapping interceptors) to change the locale under specific circumstances, for example, based on a parameter in the request.
Locale resolvers and interceptors are defined in the
org.springframework.web.servlet.i18n
package and are configured in your application
context in the normal way. Here is a selection of the locale resolvers included in
Spring.
In addition to obtaining the client’s locale, it is often useful to know their time zone.
The LocaleContextResolver
interface offers an extension to LocaleResolver
that allows
resolvers to provide a richer LocaleContext
, which may include time zone information.
When available, the user’s TimeZone
can be obtained using the
RequestContext.getTimeZone()
method. Time zone information will automatically be used
by Date/Time Converter
and Formatter
objects registered with Spring’s
ConversionService
.
This locale resolver inspects the accept-language
header in the request that was sent
by the client (e.g., a web browser). Usually this header field contains the locale of
the client’s operating system. Note that this resolver does not support time zone
information.
This locale resolver inspects a Cookie
that might exist on the client to see if a
Locale
or TimeZone
is specified. If so, it uses the specified details. Using the
properties of this locale resolver, you can specify the name of the cookie as well as the
maximum age. Find below an example of defining a CookieLocaleResolver
.
<bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"> <property name="cookieName" value="clientlanguage"/> <!-- in seconds. If set to -1, the cookie is not persisted (deleted when browser shuts down) --> <property name="cookieMaxAge" value="100000"> </bean>
Table 21.4. CookieLocaleResolver properties
Property | Default | Description |
---|---|---|
cookieName | classname + LOCALE | The name of the cookie |
cookieMaxAge | Integer.MAX_INT | The maximum time a cookie will stay persistent on the client. If -1 is specified, the cookie will not be persisted; it will only be available until the client shuts down their browser. |
cookiePath | / | Limits the visibility of the cookie to a certain part of your site. When cookiePath is specified, the cookie will only be visible to that path and the paths below it. |
The SessionLocaleResolver
allows you to retrieve Locale
and TimeZone
from the
session that might be associated with the user’s request.
You can enable changing of locales by adding the LocaleChangeInterceptor
to one of the
handler mappings (see Section 21.4, “Handler mappings”). It will detect a parameter in the request
and change the locale. It calls setLocale()
on the LocaleResolver
that also exists
in the context. The following example shows that calls to all *.view
resources
containing a parameter named siteLanguage
will now change the locale. So, for example,
a request for the following URL, http://www.sf.net/home.view?siteLanguage=nl
will
change the site language to Dutch.
<bean id="localeChangeInterceptor" class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"> <property name="paramName" value="siteLanguage"/> </bean> <bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/> <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping"> <property name="interceptors"> <list> <ref bean="localeChangeInterceptor"/> </list> </property> <property name="mappings"> <value>/**/*.view=someController</value> </property> </bean>
You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application, thereby enhancing user experience. A theme is a collection of static resources, typically style sheets and images, that affect the visual style of the application.
To use themes in your web application, you must set up an implementation of the
org.springframework.ui.context.ThemeSource
interface. The WebApplicationContext
interface extends ThemeSource
but delegates its responsibilities to a dedicated
implementation. By default the delegate will be an
org.springframework.ui.context.support.ResourceBundleThemeSource
implementation that
loads properties files from the root of the classpath. To use a custom ThemeSource
implementation or to configure the base name prefix of the ResourceBundleThemeSource
,
you can register a bean in the application context with the reserved name themeSource
.
The web application context automatically detects a bean with that name and uses it.
When using the ResourceBundleThemeSource
, a theme is defined in a simple properties
file. The properties file lists the resources that make up the theme. Here is an example:
styleSheet=/themes/cool/style.css background=/themes/cool/img/coolBg.jpg
The keys of the properties are the names that refer to the themed elements from view
code. For a JSP, you typically do this using the spring:theme
custom tag, which is
very similar to the spring:message
tag. The following JSP fragment uses the theme
defined in the previous example to customize the look and feel:
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> <html> <head> <link rel="stylesheet" href="<spring:theme code=''styleSheet''/>" type="text/css"/> </head> <body style="background=<spring:theme code=''background''/>"> ... </body> </html>
By default, the ResourceBundleThemeSource
uses an empty base name prefix. As a result,
the properties files are loaded from the root of the classpath. Thus you would put the
cool.properties
theme definition in a directory at the root of the classpath, for
example, in /WEB-INF/classes
. The ResourceBundleThemeSource
uses the standard Java
resource bundle loading mechanism, allowing for full internationalization of themes. For
example, we could have a /WEB-INF/classes/cool_nl.properties
that references a special
background image with Dutch text on it.
After you define themes, as in the preceding section, you decide which theme to use. The
DispatcherServlet
will look for a bean named themeResolver
to find out which
ThemeResolver
implementation to use. A theme resolver works in much the same way as a
LocaleResolver
. It detects the theme to use for a particular request and can also
alter the request’s theme. The following theme resolvers are provided by Spring:
Table 21.5. ThemeResolver implementations
Class | Description |
---|---|
| Selects a fixed theme, set using the |
| The theme is maintained in the user’s HTTP session. It only needs to be set once for each session, but is not persisted between sessions. |
| The selected theme is stored in a cookie on the client. |
Spring also provides a ThemeChangeInterceptor
that allows theme changes on every
request with a simple request parameter.
Spring’s built-in multipart support handles file uploads in web applications. You enable
this multipart support with pluggable MultipartResolver
objects, defined in the
org.springframework.web.multipart
package. Spring provides one MultipartResolver
implementation for use with Commons
FileUpload and another for use with Servlet 3.0 multipart request parsing.
By default, Spring does no multipart handling, because some developers want to handle
multiparts themselves. You enable Spring multipart handling by adding a multipart
resolver to the web application’s context. Each request is inspected to see if it
contains a multipart. If no multipart is found, the request continues as expected. If a
multipart is found in the request, the MultipartResolver
that has been declared in
your context is used. After that, the multipart attribute in your request is treated
like any other attribute.
The following example shows how to use the CommonsMultipartResolver
:
<bean id="multipartResolver" class="org.springframework.web.multipart.commons.CommonsMultipartResolver"> <!-- one of the properties available; the maximum file size in bytes --> <property name="maxUploadSize" value="100000"/> </bean>
Of course you also need to put the appropriate jars in your classpath for the multipart
resolver to work. In the case of the CommonsMultipartResolver
, you need to use
commons-fileupload.jar
.
When the Spring DispatcherServlet
detects a multi-part request, it activates the
resolver that has been declared in your context and hands over the request. The resolver
then wraps the current HttpServletRequest
into a MultipartHttpServletRequest
that
supports multipart file uploads. Using the MultipartHttpServletRequest
, you can get
information about the multiparts contained by this request and actually get access to
the multipart files themselves in your controllers.
In order to use Servlet 3.0 based multipart parsing, you need to mark the
DispatcherServlet
with a "multipart-config"
section in web.xml
, or with a
javax.servlet.MultipartConfigElement
in programmatic Servlet registration, or in case
of a custom Servlet class possibly with a javax.servlet.annotation.MultipartConfig
annotation on your Servlet class. Configuration settings such as maximum sizes or
storage locations need to be applied at that Servlet registration level as Servlet 3.0
does not allow for those settings to be done from the MultipartResolver.
Once Servlet 3.0 multipart parsing has been enabled in one of the above mentioned ways
you can add the StandardServletMultipartResolver
to your Spring configuration:
<bean id="multipartResolver" class="org.springframework.web.multipart.support.StandardServletMultipartResolver"> </bean>
After the MultipartResolver
completes its job, the request is processed like any
other. First, create a form with a file input that will allow the user to upload a form.
The encoding attribute ( enctype="multipart/form-data"
) lets the browser know how to
encode the form as multipart request:
<html> <head> <title>Upload a file please</title> </head> <body> <h1>Please upload a file</h1> <form method="post" action="/form" enctype="multipart/form-data"> <input type="text" name="name"/> <input type="file" name="file"/> <input type="submit"/> </form> </body> </html>
The next step is to create a controller that handles the file upload. This controller is
very similar to a normal annotated @Controller
, except that we
use MultipartHttpServletRequest
or MultipartFile
in the method parameters:
@Controller public class FileUploadController { @RequestMapping(path = "/form", method = RequestMethod.POST) public String handleFormUpload(@RequestParam("name") String name, @RequestParam("file") MultipartFile file) { if (!file.isEmpty()) { byte[] bytes = file.getBytes(); // store the bytes somewhere return "redirect:uploadSuccess"; } return "redirect:uploadFailure"; } }
Note how the @RequestParam
method parameters map to the input elements declared in the
form. In this example, nothing is done with the byte[]
, but in practice you can save
it in a database, store it on the file system, and so on.
When using Servlet 3.0 multipart parsing you can also use javax.servlet.http.Part
for
the method parameter:
@Controller public class FileUploadController { @RequestMapping(path = "/form", method = RequestMethod.POST) public String handleFormUpload(@RequestParam("name") String name, @RequestParam("file") Part file) { InputStream inputStream = file.getInputStream(); // store bytes from uploaded file somewhere return "redirect:uploadSuccess"; } }
Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. All of the above examples and configuration apply here as well. However, unlike browsers that typically submit files and simple form fields, a programmatic client can also send more complex data of a specific content type — for example a multipart request with a file and second part with JSON formatted data:
POST /someUrl Content-Type: multipart/mixed --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="meta-data" Content-Type: application/json; charset=UTF-8 Content-Transfer-Encoding: 8bit { "name": "value" } --edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp Content-Disposition: form-data; name="file-data"; filename="file.properties" Content-Type: text/xml Content-Transfer-Encoding: 8bit ... File Data ...
You could access the part named "meta-data" with a @RequestParam("meta-data") String
metadata
controller method argument. However, you would probably prefer to accept a
strongly typed object initialized from the JSON formatted data in the body of the
request part, very similar to the way @RequestBody
converts the body of a
non-multipart request to a target object with the help of an HttpMessageConverter
.
You can use the @RequestPart
annotation instead of the @RequestParam
annotation for
this purpose. It allows you to have the content of a specific multipart passed through
an HttpMessageConverter
taking into consideration the 'Content-Type'
header of the
multipart:
@RequestMapping(path = "/someUrl", method = RequestMethod.POST) public String onSubmit(@RequestPart("meta-data") MetaData metadata, @RequestPart("file-data") MultipartFile file) { // ... }
Notice how MultipartFile
method arguments can be accessed with @RequestParam
or with
@RequestPart
interchangeably. However, the @RequestPart("meta-data") MetaData
method
argument in this case is read as JSON content based on its 'Content-Type'
header and
converted with the help of the MappingJackson2HttpMessageConverter
.
Spring HandlerExceptionResolver
implementations deal with unexpected exceptions that
occur during controller execution. A HandlerExceptionResolver
somewhat resembles the
exception mappings you can define in the web application descriptor web.xml
. However,
they provide a more flexible way to do so. For example they provide information about
which handler was executing when the exception was thrown. Furthermore, a programmatic
way of handling exceptions gives you more options for responding appropriately before
the request is forwarded to another URL (the same end result as when you use the Servlet
specific exception mappings).
Besides implementing the HandlerExceptionResolver
interface, which is only a matter of
implementing the resolveException(Exception, Handler)
method and returning a
ModelAndView
, you may also use the provided SimpleMappingExceptionResolver
or create
@ExceptionHandler
methods. The SimpleMappingExceptionResolver
enables you to take
the class name of any exception that might be thrown and map it to a view name. This is
functionally equivalent to the exception mapping feature from the Servlet API, but it is
also possible to implement more finely grained mappings of exceptions from different
handlers. The @ExceptionHandler
annotation on the other hand can be used on methods
that should be invoked to handle an exception. Such methods may be defined locally
within an @Controller
or may apply to many @Controller
classes when defined within an
@ControllerAdvice
class. The following sections explain this in more detail.
The HandlerExceptionResolver
interface and the SimpleMappingExceptionResolver
implementations allow you to map Exceptions to specific views declaratively along with
some optional Java logic before forwarding to those views. However, in some cases,
especially when relying on @ResponseBody
methods rather than on view resolution, it
may be more convenient to directly set the status of the response and optionally write
error content to the body of the response.
You can do that with @ExceptionHandler
methods. When declared within a controller such
methods apply to exceptions raised by @RequestMapping
methods of that contoroller (or
any of its sub-classes). You can also declare an @ExceptionHandler
method within an
@ControllerAdvice
class in which case it handles exceptions from @RequestMapping
methods from many controllers. Below is an example of a controller-local
@ExceptionHandler
method:
@Controller public class SimpleController { // @RequestMapping methods omitted ... @ExceptionHandler(IOException.class) public ResponseEntity<String> handleIOException(IOException ex) { // prepare responseEntity return responseEntity; } }
The @ExceptionHandler
value can be set to an array of Exception types. If an exception
is thrown that matches one of the types in the list, then the method annotated with the
matching @ExceptionHandler
will be invoked. If the annotation value is not set then
the exception types listed as method arguments are used.
Much like standard controller methods annotated with a @RequestMapping
annotation, the
method arguments and return values of @ExceptionHandler
methods can be flexible. For
example, the HttpServletRequest
can be accessed in Servlet environments and the
PortletRequest
in Portlet environments. The return type can be a String
, which is
interpreted as a view name, a ModelAndView
object, a ResponseEntity
, or you can also
add the @ResponseBody
to have the method return value converted with message
converters and written to the response stream.
Spring MVC may raise a number of exceptions while processing a request. The
SimpleMappingExceptionResolver
can easily map any exception to a default error view as
needed. However, when working with clients that interpret responses in an automated way
you will want to set specific status code on the response. Depending on the exception
raised the status code may indicate a client error (4xx) or a server error (5xx).
The DefaultHandlerExceptionResolver
translates Spring MVC exceptions to specific error
status codes. It is registered by default with the MVC namespace, the MVC Java config,
and also by the the DispatcherServlet
(i.e. when not using the MVC namespace or Java
config). Listed below are some of the exceptions handled by this resolver and the
corresponding status codes:
Exception | HTTP Status Code |
---|---|
| 400 (Bad Request) |
| 500 (Internal Server Error) |
| 406 (Not Acceptable) |
| 415 (Unsupported Media Type) |
| 400 (Bad Request) |
| 500 (Internal Server Error) |
| 405 (Method Not Allowed) |
| 400 (Bad Request) |
| 400 (Bad Request) |
| 400 (Bad Request) |
| 404 (Not Found) |
| 404 (Not Found) |
| 400 (Bad Request) |
The DefaultHandlerExceptionResolver
works transparently by setting the status of the
response. However, it stops short of writing any error content to the body of the
response while your application may need to add developer-friendly content to every
error response for example when providing a REST API. You can prepare a ModelAndView
and render error content through view resolution — i.e. by configuring a
ContentNegotiatingViewResolver
, MappingJackson2JsonView
, and so on. However, you may
prefer to use @ExceptionHandler
methods instead.
If you prefer to write error content via @ExceptionHandler
methods you can extend
ResponseEntityExceptionHandler
instead. This is a convenient base for
@ControllerAdvice
classes providing an @ExceptionHandler
method to handle standard
Spring MVC exceptions and return ResponseEntity
. That allows you to customize the
response and write error content with message converters. See the
ResponseEntityExceptionHandler
javadocs for more details.
A business exception can be annotated with @ResponseStatus
. When the exception is
raised, the ResponseStatusExceptionResolver
handles it by setting the status of the
response accordingly. By default the DispatcherServlet
registers the
ResponseStatusExceptionResolver
and it is available for use.
When the status of the response is set to an error status code and the body of the
response is empty, Servlet containers commonly render an HTML formatted error page. To
customize the default error page of the container, you can declare an <error-page>
element in web.xml
. Up until Servlet 3, that element had to be mapped to a specific
status code or exception type. Starting with Servlet 3 an error page does not need to be
mapped, which effectively means the specified location customizes the default Servlet
container error page.
<error-page> <location>/error</location> </error-page>
Note that the actual location for the error page can be a JSP page or some other URL
within the container including one handled through an @Controller
method:
When writing error information, the status code and the error message set on the
HttpServletResponse
can be accessed through request attributes in a controller:
@Controller public class ErrorController { @RequestMapping(path="/error", produces="application/json") @ResponseBody public Map<String, Object> handle(HttpServletRequest request) { Map<String, Object> map = new HashMap<String, Object>(); map.put("status", request.getAttribute("javax.servlet.error.status_code")); map.put("reason", request.getAttribute("javax.servlet.error.message")); return map; } }
or in a JSP:
<%@ page contentType="application/json" pageEncoding="UTF-8"%> { status:<%=request.getAttribute("javax.servlet.error.status_code") %>, reason:<%=request.getAttribute("javax.servlet.error.message") %> }
The Spring Security project provides features
to protect web applications from malicious exploits. Check out the reference documentation in the sections on
"CSRF protection",
"Security Response Headers", and also
"Spring MVC Integration".
Note that using Spring Security to secure the application is not necessarily required for all features.
For example CSRF protection can be added simply by adding the CsrfFilter
and
CsrfRequestDataValueProcessor
to your configuration. See the
Spring MVC Showcase
for an example.
Another option is to use a framework dedicated to Web Security. HDIV is one such framework and integrates with Spring MVC.
For a lot of projects, sticking to established conventions and having reasonable
defaults is just what they (the projects) need, and Spring Web MVC now has explicit
support for convention over configuration. What this means is that if you establish
a set of naming conventions and suchlike, you can substantially cut down on the
amount of configuration that is required to set up handler mappings, view resolvers,
ModelAndView
instances, etc. This is a great boon with regards to rapid prototyping,
and can also lend a degree of (always good-to-have) consistency across a codebase should
you choose to move forward with it into production.
Convention-over-configuration support addresses the three core areas of MVC: models, views, and controllers.
The ControllerClassNameHandlerMapping
class is a HandlerMapping
implementation that
uses a convention to determine the mapping between request URLs and the Controller
instances that are to handle those requests.
Consider the following simple Controller
implementation. Take special notice of the
name of the class.
public class ViewShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // the implementation is not hugely important for this example... } }
Here is a snippet from the corresponding Spring Web MVC configuration file:
<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewShoppingCart" class="x.y.z.ViewShoppingCartController"> <!-- inject dependencies as required... --> </bean>
The ControllerClassNameHandlerMapping
finds all of the various handler (or
Controller
) beans defined in its application context and strips Controller
off the
name to define its handler mappings. Thus, ViewShoppingCartController
maps to the
/viewshoppingcart*
request URL.
Let’s look at some more examples so that the central idea becomes immediately familiar.
(Notice all lowercase in the URLs, in contrast to camel-cased Controller
class names.)
WelcomeController
maps to the /welcome*
request URL
HomeController
maps to the /home*
request URL
IndexController
maps to the /index*
request URL
RegisterController
maps to the /register*
request URL
In the case of MultiActionController
handler classes, the mappings generated are
slightly more complex. The Controller
names in the following examples are assumed to
be MultiActionController
implementations:
AdminController
maps to the /admin/*
request URL
CatalogController
maps to the /catalog/*
request URL
If you follow the convention of naming your Controller
implementations as
xxxController
, the ControllerClassNameHandlerMapping
saves you the tedium of
defining and maintaining a potentially looooong SimpleUrlHandlerMapping
(or
suchlike).
The ControllerClassNameHandlerMapping
class extends the AbstractHandlerMapping
base
class so you can define HandlerInterceptor
instances and everything else just as you
would with many other HandlerMapping
implementations.
The ModelMap
class is essentially a glorified Map
that can make adding objects that
are to be displayed in (or on) a View
adhere to a common naming convention. Consider
the following Controller
implementation; notice that objects are added to the
ModelAndView
without any associated name specified.
public class DisplayShoppingCartController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { List cartItems = // get a List of CartItem objects User user = // get the User doing the shopping ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name mav.addObject(cartItems); <-- look ma, no name, just the object mav.addObject(user); <-- and again ma! return mav; } }
The ModelAndView
class uses a ModelMap
class that is a custom Map
implementation
that automatically generates a key for an object when an object is added to it. The
strategy for determining the name for an added object is, in the case of a scalar object
such as User
, to use the short class name of the object’s class. The following
examples are names that are generated for scalar objects put into a ModelMap
instance.
x.y.User
instance added will have the name user
generated.
x.y.Registration
instance added will have the name registration
generated.
x.y.Foo
instance added will have the name foo
generated.
java.util.HashMap
instance added will have the name hashMap
generated. You
probably want to be explicit about the name in this case because hashMap
is less
than intuitive.
null
will result in an IllegalArgumentException
being thrown. If the object
(or objects) that you are adding could be null
, then you will also want to be
explicit about the name.
The strategy for generating a name after adding a Set
or a List
is to peek into the
collection, take the short class name of the first object in the collection, and use
that with List
appended to the name. The same applies to arrays although with arrays
it is not necessary to peek into the array contents. A few examples will make the
semantics of name generation for collections clearer:
x.y.User[]
array with zero or more x.y.User
elements added will have the name
userList
generated.
x.y.Foo[]
array with zero or more x.y.User
elements added will have the name
fooList
generated.
java.util.ArrayList
with one or more x.y.User
elements added will have the name
userList
generated.
java.util.HashSet
with one or more x.y.Foo
elements added will have the name
fooList
generated.
java.util.ArrayList
will not be added at all (in effect, the
addObject(..)
call will essentially be a no-op).
The RequestToViewNameTranslator
interface determines a logical View
name when no
such logical view name is explicitly supplied. It has just one implementation, the
DefaultRequestToViewNameTranslator
class.
The DefaultRequestToViewNameTranslator
maps request URLs to logical view names, as
with this example:
public class RegistrationController implements Controller { public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) { // process the request... ModelAndView mav = new ModelAndView(); // add data as necessary to the model... return mav; // notice that no View or logical view name has been set } }
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <!-- this bean with the well known name generates view names for us --> <bean id="viewNameTranslator" class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/> <bean class="x.y.RegistrationController"> <!-- inject dependencies as necessary --> </bean> <!-- maps request URLs to Controller names --> <bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/> <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver"> <property name="prefix" value="/WEB-INF/jsp/"/> <property name="suffix" value=".jsp"/> </bean> </beans>
Notice how in the implementation of the handleRequest(..)
method no View
or logical
view name is ever set on the ModelAndView
that is returned. The
DefaultRequestToViewNameTranslator
is tasked with generating a logical view name
from the URL of the request. In the case of the above RegistrationController
, which is
used in conjunction with the ControllerClassNameHandlerMapping
, a request URL of
http://localhost/registration.html
results in a logical view name of registration
being generated by the DefaultRequestToViewNameTranslator
. This logical view name is
then resolved into the /WEB-INF/jsp/registration.jsp
view by the
InternalResourceViewResolver
bean.
Tip | |
---|---|
You do not need to define a |
Of course, if you need to change the default settings, then you do need to configure
your own DefaultRequestToViewNameTranslator
bean explicitly. Consult the comprehensive
DefaultRequestToViewNameTranslator
javadocs for details on the various properties
that can be configured.
A good HTTP caching strategy can significantly improve the performance of a web application
and the experience of its clients. The 'Cache-Control'
HTTP response header is mostly
responsible for this, along with conditional headers such as 'Last-Modified'
and 'ETag'
.
The 'Cache-Control'
HTTP response header advises private caches (e.g. browsers) and
public caches (e.g. proxies) on how they can cache HTTP responses for further reuse.
An ETag (entity tag) is an HTTP response header
returned by an HTTP/1.1 compliant web server used to determine change in content at a
given URL. It can be considered to be the more sophisticated successor to the
Last-Modified
header. When a server returns a representation with an ETag header, the
client can use this header in subsequent GETs, in an If-None-Match
header. If the
content has not changed, the server returns 304: Not Modified
.
This section describes the different choices available to configure HTTP caching in a Spring Web MVC application.
Spring Web MVC supports many use cases and ways to configure "Cache-Control" headers for an application. While RFC 7234 Section 5.2.2 completely describes that header and its possible directives, there are several ways to address the most common cases.
Spring Web MVC uses a configuration convention in several of its APIs:
setCachePeriod(int seconds)
:
-1
value won’t generate a 'Cache-Control'
response header.
0
value will prevent caching using the 'Cache-Control: no-store'
directive.
n > 0
value will cache the given response for n
seconds using the
'Cache-Control: max-age=n'
directive.
The CacheControl
builder
class simply describes the available "Cache-Control" directives and makes it easier to
build your own HTTP caching strategy. Once built, a CacheControl
instance can then be
accepted as an argument in several Spring Web MVC APIs.
// Cache for an hour - "Cache-Control: max-age=3600" CacheControl ccCacheOneHour = CacheControl.maxAge(1, TimeUnit.HOURS); // Prevent caching - "Cache-Control: no-store" CacheControl ccNoStore = CacheControl.noStore(); // Cache for ten days in public and private caches, // public caches should not transform the response // "Cache-Control: max-age=864000, public, no-transform" CacheControl ccCustom = CacheControl.maxAge(10, TimeUnit.DAYS) .noTransform().cachePublic();
Static resources should be served with appropriate 'Cache-Control'
and conditional
headers for optimal performance.
Configuring a ResourceHttpRequestHandler
for serving
static resources not only natively writes 'Last-Modified'
headers by reading a file’s
metadata, but also 'Cache-Control'
headers if properly configured.
You can set the cachePeriod
attribute on a ResourceHttpRequestHandler
or use
a CacheControl
instance, which supports more specific directives:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**") .addResourceLocations("/public-resources/") .setCacheControl(CacheControl.maxAge(1, TimeUnit.HOURS).cachePublic()); } }
And in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/"> <mvc:cache-control max-age="3600" cache-public="true"/> </mvc:resources>
Controllers can support 'Cache-Control'
, 'ETag'
, and/or 'If-Modified-Since'
HTTP requests;
this is indeed recommended if a 'Cache-Control'
header is to be set on the response.
This involves calculating a lastModified long
and/or an Etag value for a given request,
comparing it against the 'If-Modified-Since'
request header value, and potentially returning
a response with status code 304 (Not Modified).
As described in the section called “Using HttpEntity”, Controllers can interact with the request/response using
HttpEntity
types. Controllers returning ResponseEntity
can include HTTP caching information
in responses like this:
@RequestMapping("/book/{id}") public ResponseEntity<Book> showBook(@PathVariable Long id) { Book book = findBook(id); String version = book.getVersion(); return ResponseEntity .ok() .cacheControl(CacheControl.maxAge(30, TimeUnit.DAYS)) .eTag(version) // lastModified is also available .body(book); }
Doing this will not only include 'ETag'
and 'Cache-Control'
headers in the response, it will also convert the
response to an HTTP 304 Not Modified
response with an empty body if the conditional headers sent by the client
match the caching information set by the Controller.
An @RequestMapping
method may also wish to support the same behavior.
This can be achieved as follows:
@RequestMapping public String myHandleMethod(WebRequest webRequest, Model model) { long lastModified = // 1. application-specific calculation if (request.checkNotModified(lastModified)) { // 2. shortcut exit - no further processing necessary return null; } // 3. or otherwise further request processing, actually preparing content model.addAttribute(...); return "myViewName"; }
There are two key elements here: calling request.checkNotModified(lastModified)
and
returning null
. The former sets the response status to 304 before it returns true
.
The latter, in combination with the former, causes Spring MVC to do no further
processing of the request.
Note that there are 3 variants for this:
request.checkNotModified(lastModified)
compares lastModified with the
'If-Modified-Since'
request header
request.checkNotModified(eTag)
compares eTag with the 'ETag'
request header
request.checkNotModified(eTag, lastModified)
does both, meaning that both
conditions should be valid for the server to issue an HTTP 304 Not Modified
response
Support for ETags is provided by the Servlet filter ShallowEtagHeaderFilter
. It is a
plain Servlet Filter, and thus can be used in combination with any web framework. The
ShallowEtagHeaderFilter
filter creates so-called shallow ETags (as opposed to deep
ETags, more about that later).The filter caches the content of the rendered JSP (or
other content), generates an MD5 hash over that, and returns that as an ETag header in
the response. The next time a client sends a request for the same resource, it uses that
hash as the If-None-Match
value. The filter detects this, renders the view again, and
compares the two hashes. If they are equal, a 304
is returned. This filter will not
save processing power, as the view is still rendered. The only thing it saves is
bandwidth, as the rendered response is not sent back over the wire.
Note that this strategy saves network bandwidth but not CPU, as the full response must be computed for each request. Other strategies at the controller level (described above) can save network bandwidth and avoid computation.
You configure the ShallowEtagHeaderFilter
in web.xml
:
<filter> <filter-name>etagFilter</filter-name> <filter-class>org.springframework.web.filter.ShallowEtagHeaderFilter</filter-class> </filter> <filter-mapping> <filter-name>etagFilter</filter-name> <servlet-name>petclinic</servlet-name> </filter-mapping>
Or in Servlet 3.0+ environments,
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer { // ... @Override protected Filter[] getServletFilters() { return new Filter[] { new ShallowEtagHeaderFilter() }; } }
See Section 21.15, “Code-based Servlet container initialization” for more details.
In a Servlet 3.0+ environment, you have the option of configuring the Servlet container
programmatically as an alternative or in combination with a web.xml
file. Below is an
example of registering a DispatcherServlet
:
import org.springframework.web.WebApplicationInitializer; public class MyWebApplicationInitializer implements WebApplicationInitializer { @Override public void onStartup(ServletContext container) { XmlWebApplicationContext appContext = new XmlWebApplicationContext(); appContext.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml"); ServletRegistration.Dynamic registration = container.addServlet("dispatcher", new DispatcherServlet(appContext)); registration.setLoadOnStartup(1); registration.addMapping("/"); } }
WebApplicationInitializer
is an interface provided by Spring MVC that ensures your
implementation is detected and automatically used to initialize any Servlet 3 container.
An abstract base class implementation of WebApplicationInitializer
named
AbstractDispatcherServletInitializer
makes it even easier to register the
DispatcherServlet
by simply overriding methods to specify the servlet mapping and the
location of the DispatcherServlet
configuration:
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer { @Override protected Class<?>[] getRootConfigClasses() { return null; } @Override protected Class<?>[] getServletConfigClasses() { return new Class[] { MyWebConfig.class }; } @Override protected String[] getServletMappings() { return new String[] { "/" }; } }
The above example is for an application that uses Java-based Spring configuration. If
using XML-based Spring configuration, extend directly from
AbstractDispatcherServletInitializer
:
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer { @Override protected WebApplicationContext createRootApplicationContext() { return null; } @Override protected WebApplicationContext createServletApplicationContext() { XmlWebApplicationContext cxt = new XmlWebApplicationContext(); cxt.setConfigLocation("/WEB-INF/spring/dispatcher-config.xml"); return cxt; } @Override protected String[] getServletMappings() { return new String[] { "/" }; } }
AbstractDispatcherServletInitializer
also provides a convenient way to add Filter
instances and have them automatically mapped to the DispatcherServlet
:
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer { // ... @Override protected Filter[] getServletFilters() { return new Filter[] { new HiddenHttpMethodFilter(), new CharacterEncodingFilter() }; } }
Each filter is added with a default name based on its concrete type and automatically
mapped to the DispatcherServlet
.
The isAsyncSupported
protected method of AbstractDispatcherServletInitializer
provides a single place to enable async support on the DispatcherServlet
and all
filters mapped to it. By default this flag is set to true
.
Finally, if you need to further customize the DispatcherServlet
itself, you can
override the createDispatcherServlet
method.
Section 21.2.1, “Special Bean Types In the WebApplicationContext” and Section 21.2.2, “Default DispatcherServlet Configuration” explained about Spring
MVC’s special beans and the default implementations used by the DispatcherServlet
. In
this section you’ll learn about two additional ways of configuring Spring MVC. Namely
the MVC Java config and the MVC XML namespace.
The MVC Java config and the MVC namespace provide similar default configuration that
overrides the DispatcherServlet
defaults. The goal is to spare most applications from
having to having to create the same configuration and also to provide higher-level
constructs for configuring Spring MVC that serve as a simple starting point and require
little or no prior knowledge of the underlying configuration.
You can choose either the MVC Java config or the MVC namespace depending on your preference. Also as you will see further below, with the MVC Java config it is easier to see the underlying configuration as well as to make fine-grained customizations directly to the created Spring MVC beans. But let’s start from the beginning.
To enable MVC Java config add the annotation @EnableWebMvc
to one of your
@Configuration
classes:
@Configuration @EnableWebMvc public class WebConfig { }
To achieve the same in XML use the mvc:annotation-driven
element in your
DispatcherServlet context (or in your root context if you have no DispatcherServlet
context defined):
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <mvc:annotation-driven /> </beans>
The above registers a RequestMappingHandlerMapping
, a RequestMappingHandlerAdapter
,
and an ExceptionHandlerExceptionResolver
(among others) in support of processing
requests with annotated controller methods using annotations such as @RequestMapping
,
@ExceptionHandler
, and others.
It also enables the following:
@NumberFormat
annotation
through the ConversionService
.
@DateTimeFormat
annotation.
@Controller
inputs with @Valid
, if
a JSR-303 Provider is present on the classpath.
HttpMessageConverter support for @RequestBody
method parameters and @ResponseBody
method return values from @RequestMapping
or @ExceptionHandler
methods.
This is the complete list of HttpMessageConverters set up by mvc:annotation-driven:
ByteArrayHttpMessageConverter
converts byte arrays.
StringHttpMessageConverter
converts strings.
ResourceHttpMessageConverter
converts to/from
org.springframework.core.io.Resource
for all media types.
SourceHttpMessageConverter
converts to/from a javax.xml.transform.Source
.
FormHttpMessageConverter
converts form data to/from a MultiValueMap<String,
String>
.
Jaxb2RootElementHttpMessageConverter
converts Java objects to/from XML — added if
JAXB2 is present and Jackson 2 XML extension is not present on the classpath.
MappingJackson2HttpMessageConverter
converts to/from JSON — added if Jackson 2
is present on the classpath.
MappingJackson2XmlHttpMessageConverter
converts to/from XML — added if
Jackson 2 XML extension is present
on the classpath.
AtomFeedHttpMessageConverter
converts Atom feeds — added if Rome is present on the
classpath.
RssChannelHttpMessageConverter
converts RSS feeds — added if Rome is present on
the classpath.
To customize the default configuration in Java you simply implement the
WebMvcConfigurer
interface or more likely extend the class WebMvcConfigurerAdapter
and override the methods you need:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { // Override configuration methods... }
To customize the default configuration of <mvc:annotation-driven />
check what
attributes and sub-elements it supports. You can view the
Spring MVC XML schema or use the code
completion feature of your IDE to discover what attributes and sub-elements are
available.
By default formatters for Number
and Date
types are installed, including support for
the @NumberFormat
and @DateTimeFormat
annotations. Full support for the Joda Time
formatting library is also installed if Joda Time is present on the classpath. To
register custom formatters and converters, override the addFormatters
method:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addFormatters(FormatterRegistry registry) { // Add formatters and/or converters } }
In the MVC namespace the same defaults apply when <mvc:annotation-driven>
is added.
To register custom formatters and converters simply supply a ConversionService
:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <mvc:annotation-driven conversion-service="conversionService"/> <bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean"> <property name="converters"> <set> <bean class="org.example.MyConverter"/> </set> </property> <property name="formatters"> <set> <bean class="org.example.MyFormatter"/> <bean class="org.example.MyAnnotationFormatterFactory"/> </set> </property> <property name="formatterRegistrars"> <set> <bean class="org.example.MyFormatterRegistrar"/> </set> </property> </bean> </beans>
Note | |
---|---|
See Section 8.6.4, “FormatterRegistrar SPI” and the |
Spring provides a Validator interface that can be used for validation in all layers
of an application. In Spring MVC you can configure it for use as a global Validator
instance, to be used
whenever an @Valid
or @Validated
controller method argument is encountered, and/or as a local
Validator
within a controller through an @InitBinder
method. Global and local validator
instances can be combined to provide composite validation.
Spring also supports JSR-303/JSR-349 Bean Validation
via LocalValidatorFactoryBean
which adapts the Spring org.springframework.validation.Validator
interface to the Bean Validation javax.validation.Validator
contract. This class can be
plugged into Spring MVC as a global validator as described next.
By default use of @EnableWebMvc
or <mvc:annotation-driven>
automatically registers Bean
Validation support in Spring MVC through the LocalValidatorFactoryBean
when a Bean Validation
provider is such as Hibernate Validator is detected on the classpath.
Note | |
---|---|
Sometimes it’s convenient to have a If you prefer to use the one from the MVC Java config, you’ll need to override the
|
Alternatively you can configure your own global Validator
instance:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public Validator getValidator(); { // return "global" validator } }
and in XML:
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <mvc:annotation-driven validator="globalValidator"/> </beans>
To combine global with local validation, simply add one or more local validator(s):
@Controller public class MyController { @InitBinder protected void initBinder(WebDataBinder binder) { binder.addValidators(new FooValidator()); } }
With this minimal configuration anytime an @Valid
or @Validated
method argument is encountered, it
will be validated by the configured validators. Any validation violations will automatically
be exposed as errors in the BindingResult
accessible as a method argument and also renderable
in Spring MVC HTML views.
You can configure HandlerInterceptors
or WebRequestInterceptors
to be applied to all
incoming requests or restricted to specific URL path patterns.
An example of registering interceptors in Java:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addInterceptors(InterceptorRegistry registry) { registry.addInterceptor(new LocaleInterceptor()); registry.addInterceptor(new ThemeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**"); registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*"); } }
And in XML use the <mvc:interceptors>
element:
<mvc:interceptors> <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor" /> <mvc:interceptor> <mvc:mapping path="/**"/> <mvc:exclude-mapping path="/admin/**"/> <bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor" /> </mvc:interceptor> <mvc:interceptor> <mvc:mapping path="/secure/*"/> <bean class="org.example.SecurityInterceptor" /> </mvc:interceptor> </mvc:interceptors>
You can configure how Spring MVC determines the requested media types from the client for request mapping as well as for content negotiation purposes. The available options are to check the file extension in the request URI, the "Accept" header, a request parameter, as well as to fall back on a default content type. By default, file extension in the request URI is checked first and the "Accept" header is checked next.
For file extensions in the request URI, the MVC Java config and the MVC namespace,
automatically register extensions such as .json
, .xml
, .rss
, and .atom
if the
corresponding dependencies such as Jackson, JAXB2, or Rome are present on the classpath.
Additional extensions may be not need to be registered explicitly if they can be
discovered via ServletContext.getMimeType(String)
or the Java Activation Framework
(see javax.activation.MimetypesFileTypeMap
). You can register more extensions with the
setUseRegisteredSuffixPatternMatch
method.
The introduction of ContentNegotiationManager
also enables selective suffix pattern
matching for incoming requests. For more details, see its javadocs.
Below is an example of customizing content negotiation options through the MVC Java config:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureContentNegotiation(ContentNegotiationConfigurer configurer) { configurer.favorPathExtension(false).favorParameter(true); } }
In the MVC namespace, the <mvc:annotation-driven>
element has a
content-negotiation-manager
attribute, which expects a ContentNegotiationManager
that in turn can be created with a ContentNegotiationManagerFactoryBean
:
<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" /> <bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean"> <property name="favorPathExtension" value="false" /> <property name="favorParameter" value="true" /> <property name="mediaTypes" > <value> json=application/json xml=application/xml </value> </property> </bean>
If not using the MVC Java config or the MVC namespace, you’ll need to create an instance
of ContentNegotiationManager
and use it to configure RequestMappingHandlerMapping
for request mapping purposes, and RequestMappingHandlerAdapter
and
ExceptionHandlerExceptionResolver
for content negotiation purposes.
Note that ContentNegotiatingViewResolver
now can also be configured with a
ContentNegotiatingViewResolver
, so you can use one instance throughout Spring MVC.
In more advanced cases, it may be useful to configure multiple
ContentNegotiationManager
instances that in turn may contain custom
ContentNegotiationStrategy
implementations. For example you could configure
ExceptionHandlerExceptionResolver
with a ContentNegotiationManager
that always
resolves the requested media type to "application/json"
. Or you may want to plug a
custom strategy that has some logic to select a default content type (e.g. either XML or
JSON) if no content types were requested.
This is a shortcut for defining a ParameterizableViewController
that immediately
forwards to a view when invoked. Use it in static cases when there is no Java controller
logic to execute before the view generates the response.
An example of forwarding a request for "/"
to a view called "home"
in Java:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addViewControllers(ViewControllerRegistry registry) { registry.addViewController("/").setViewName("home"); } }
And the same in XML use the <mvc:view-controller>
element:
<mvc:view-controller path="/" view-name="home"/>
The MVC config simplifies the registration of view resolvers.
The following is a Java config example that configures content negotiation view
resolution using FreeMarker HTML templates and Jackson as a default View
for
JSON rendering:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.enableContentNegotiation(new MappingJackson2JsonView()); registry.jsp(); } }
And the same in XML:
<mvc:view-resolvers> <mvc:content-negotiation> <mvc:default-views> <bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView" /> </mvc:default-views> </mvc:content-negotiation> <mvc:jsp /> </mvc:view-resolvers>
Note however that FreeMarker, Velocity, Tiles, Groovy Markup and script templates also require configuration of the underlying view technology.
The MVC namespace provides dedicated elements. For example with FreeMarker:
<mvc:view-resolvers> <mvc:content-negotiation> <mvc:default-views> <bean class="org.springframework.web.servlet.view.json.MappingJackson2JsonView" /> </mvc:default-views> </mvc:content-negotiation> <mvc:freemarker cache="false" /> </mvc:view-resolvers> <mvc:freemarker-configurer> <mvc:template-loader-path location="/freemarker" /> </mvc:freemarker-configurer>
In Java config simply add the respective "Configurer" bean:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureViewResolvers(ViewResolverRegistry registry) { registry.enableContentNegotiation(new MappingJackson2JsonView()); registry.freeMarker().cache(false); } @Bean public FreeMarkerConfigurer freeMarkerConfigurer() { FreeMarkerConfigurer configurer = new FreeMarkerConfigurer(); configurer.setTemplateLoaderPath("/WEB-INF/"); return configurer; } }
This option allows static resource requests following a particular URL pattern to be
served by a ResourceHttpRequestHandler
from any of a list of Resource
locations.
This provides a convenient way to serve static resources from locations other than the
web application root, including locations on the classpath. The cache-period
property
may be used to set far future expiration headers (1 year is the recommendation of
optimization tools such as Page Speed and YSlow) so that they will be more efficiently
utilized by the client. The handler also properly evaluates the Last-Modified
header
(if present) so that a 304
status code will be returned as appropriate, avoiding
unnecessary overhead for resources that are already cached by the client. For example,
to serve resource requests with a URL pattern of /resources/**
from a
public-resources
directory within the web application root you would use:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/"); } }
And the same in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/"/>
To serve these resources with a 1-year future expiration to ensure maximum use of the browser cache and a reduction in HTTP requests made by the browser:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**").addResourceLocations("/public-resources/").setCachePeriod(31556926); } }
And in XML:
<mvc:resources mapping="/resources/**" location="/public-resources/" cache-period="31556926"/>
For more details, see HTTP caching support for static resources.
The mapping
attribute must be an Ant pattern that can be used by
SimpleUrlHandlerMapping
, and the location
attribute must specify one or more valid
resource directory locations. Multiple resource locations may be specified using a
comma-separated list of values. The locations specified will be checked in the specified
order for the presence of the resource for any given request. For example, to enable the
serving of resources from both the web application root and from a known path of
/META-INF/public-web-resources/
in any jar on the classpath use:
@EnableWebMvc @Configuration public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**") .addResourceLocations("/", "classpath:/META-INF/public-web-resources/"); } }
And in XML:
<mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/public-web-resources/"/>
When serving resources that may change when a new version of the application is
deployed it is recommended that you incorporate a version string into the mapping
pattern used to request the resources so that you may force clients to request the
newly deployed version of your application’s resources. Support for versioned URLs is
built into the framework and can be enabled by configuring a resource chain
on the resource handler. The chain consists of one more ResourceResolver
instances followed by one or more ResourceTransformer
instances. Together they
can provide arbitrary resolution and transformation of resources.
The built-in VersionResourceResolver
can be configured with different strategies.
For example a FixedVersionStrategy
can use a property, a date, or other as the version.
A ContentVersionStrategy
uses an MD5 hash computed from the content of the resource
(known as "fingerprinting" URLs).
ContentVersionStrategy
is a good default choice to use except in cases where
it cannot be used (e.g. with JavaScript module loaders). You can configure
different version strategies against different patterns as shown below. Keep in mind
also that computing content-based versions is expensive and therefore resource chain
caching should be enabled in production.
Java config example;
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void addResourceHandlers(ResourceHandlerRegistry registry) { registry.addResourceHandler("/resources/**") .addResourceLocations("/public-resources/") .resourceChain(true).addResolver( new VersionResourceResolver().addContentVersionStrategy("/**")); } }
XML example:
<mvc:resources mapping="/resources/**" location="/public-resources/"> <mvc:resource-chain> <mvc:resource-cache /> <mvc:resolvers> <mvc:version-resolver> <mvc:content-version-strategy patterns="/**"/> </mvc:version-resolver> </mvc:resolvers> </mvc:resource-chain> </mvc:resources>
In order for the above to work the application must also
render URLs with versions. The easiest way to do that is to configure the
ResourceUrlEncodingFilter
which wraps the response and overrides its encodeURL
method.
This will work in JSPs, FreeMarker, Velocity, and any other view technology that calls
the response encodeURL
method. Alternatively, an application can also inject and
use directly the ResourceUrlProvider
bean, which is automatically declared with the MVC
Java config and the MVC namespace.
Webjars are also supported with WebJarsResourceResolver
, which is automatically registered
when the "org.webjars:webjars-locator"
library is on classpath. This resolver allows
the resource chain to resolve version agnostic libraries from HTTP GET requests
"GET /jquery/jquery.min.js"
will return resource "/jquery/1.2.0/jquery.min.js"
.
It also works by rewriting resource URLs in templates
<script src="/jquery/jquery.min.js"/> → <script src="/jquery/1.2.0/jquery.min.js"/>
.
This allows for mapping the DispatcherServlet
to "/" (thus overriding the mapping
of the container’s default Servlet), while still allowing static resource requests to be
handled by the container’s default Servlet. It configures a
DefaultServletHttpRequestHandler
with a URL mapping of "/**" and the lowest priority
relative to other URL mappings.
This handler will forward all requests to the default Servlet. Therefore it is important
that it remains last in the order of all other URL HandlerMappings
. That will be the
case if you use <mvc:annotation-driven>
or alternatively if you are setting up your
own customized HandlerMapping
instance be sure to set its order
property to a value
lower than that of the DefaultServletHttpRequestHandler
, which is Integer.MAX_VALUE
.
To enable the feature using the default setup use:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) { configurer.enable(); } }
Or in XML:
<mvc:default-servlet-handler/>
The caveat to overriding the "/" Servlet mapping is that the RequestDispatcher
for the
default Servlet must be retrieved by name rather than by path. The
DefaultServletHttpRequestHandler
will attempt to auto-detect the default Servlet for
the container at startup time, using a list of known names for most of the major Servlet
containers (including Tomcat, Jetty, GlassFish, JBoss, Resin, WebLogic, and WebSphere).
If the default Servlet has been custom configured with a different name, or if a
different Servlet container is being used where the default Servlet name is unknown,
then the default Servlet’s name must be explicitly provided as in the following example:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) { configurer.enable("myCustomDefaultServlet"); } }
Or in XML:
<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>
This allows customizing various settings related to URL mapping and path matching. For details on the individual options check out the PathMatchConfigurer API.
Below is an example in Java config:
@Configuration @EnableWebMvc public class WebConfig extends WebMvcConfigurerAdapter { @Override public void configurePathMatch(PathMatchConfigurer configurer) { configurer .setUseSuffixPatternMatch(true) .setUseTrailingSlashMatch(false) .setUseRegisteredSuffixPatternMatch(true) .setPathMatcher(antPathMatcher()) .setUrlPathHelper(urlPathHelper()); } @Bean public UrlPathHelper urlPathHelper() { //... } @Bean public PathMatcher antPathMatcher() { //... } }
And the same in XML, use the <mvc:path-matching>
element:
<mvc:annotation-driven> <mvc:path-matching suffix-pattern="true" trailing-slash="false" registered-suffixes-only="true" path-helper="pathHelper" path-matcher="pathMatcher" /> </mvc:annotation-driven> <bean id="pathHelper" class="org.example.app.MyPathHelper" /> <bean id="pathMatcher" class="org.example.app.MyPathMatcher" />
As you can see from the above examples, MVC Java config and the MVC namespace provide higher level constructs that do not require deep knowledge of the underlying beans created for you. Instead it helps you to focus on your application needs. However, at some point you may need more fine-grained control or you may simply wish to understand the underlying configuration.
The first step towards more fine-grained control is to see the underlying beans created
for you. In MVC Java config you can see the javadocs and the @Bean
methods in
WebMvcConfigurationSupport
. The configuration in this class is automatically imported
through the @EnableWebMvc
annotation. In fact if you open @EnableWebMvc
you can see
the @Import
statement.
The next step towards more fine-grained control is to customize a property on one of the
beans created in WebMvcConfigurationSupport
or perhaps to provide your own instance.
This requires two things — remove the @EnableWebMvc
annotation in order to prevent
the import and then extend from DelegatingWebMvcConfiguration
, a subclass of
WebMvcConfigurationSupport
.
Here is an example:
@Configuration public class WebConfig extends DelegatingWebMvcConfiguration { @Override public void addInterceptors(InterceptorRegistry registry){ // ... } @Override @Bean public RequestMappingHandlerAdapter requestMappingHandlerAdapter() { // Create or let "super" create the adapter // Then customize one of its properties } }
Note | |
---|---|
An application should have only one configuration extending Modifying beans in this way does not prevent you from using any of the higher-level
constructs shown earlier in this section. |
Fine-grained control over the configuration created for you is a bit harder with the MVC namespace.
If you do need to do that, rather than replicating the configuration it provides,
consider configuring a BeanPostProcessor
that detects the bean you want to customize
by type and then modifying its properties as necessary. For example:
@Component public class MyPostProcessor implements BeanPostProcessor { public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException { if (bean instanceof RequestMappingHandlerAdapter) { // Modify properties of the adapter } } }
Note that MyPostProcessor
needs to be included in an <component scan />
in order for
it to be detected or if you prefer you can declare it explicitly with an XML bean
declaration.