Spring Web MVC is the original web framework built on the Servlet API and included in the Spring Framework from the very beginning. The formal name "Spring Web MVC" comes from the name of its source module spring-webmvc but it is more commonly known as "Spring MVC".
Parallel to Spring Web MVC, Spring Framework 5.0 introduced a reactive stack, web framework whose name Spring WebFlux is also based on its source module spring-webflux. This section covers Spring Web MVC. The next section covers Spring WebFlux.
For baseline information and compatibility with Servlet container and Java EE version ranges please visit the Spring Framework Wiki.
Spring MVC, like many other web frameworks, is designed around the front controller
pattern where a central Servlet, the DispatcherServlet, provides a shared algorithm
for request processing while actual work is performed by configurable, delegate components.
This model is flexible and supports diverse workflows.
The DispatcherServlet, as any Servlet, needs to be declared and mapped according
to the Servlet specification using Java configuration or in web.xml.
In turn the DispatcherServlet uses Spring configuration to discover
the delegate components it needs for request mapping, view resolution, exception
handling, and more.
Below is an example of the Java configuration that registers and initializes
the DispatcherServlet. This class is auto-detected by the Servlet container
(see Servlet Config):
public class MyWebApplicationInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext servletCxt) {
// Load Spring web application configuration
AnnotationConfigWebApplicationContext ac = new AnnotationConfigWebApplicationContext();
ac.register(AppConfig.class);
ac.refresh();
// Create and register the DispatcherServlet
DispatcherServlet servlet = new DispatcherServlet(ac);
ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
registration.setLoadOnStartup(1);
registration.addMapping("/app/*");
}
}|
Note
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In addition to using the ServletContext API directly, you can also extend
|
Below is an example of web.xml configuration to register and initialize the DispatcherServlet:
<web-app>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/app-context.xml</param-value>
</context-param>
<servlet>
<servlet-name>app</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>app</servlet-name>
<url-pattern>/app/*</url-pattern>
</servlet-mapping>
</web-app>|
Note
|
Spring Boot follows a different initialization sequence. Rather than hooking into
the lifecycle of the Servlet container, Spring Boot uses Spring configuration to
bootstrap itself and the embedded Servlet container. |
DispatcherServlet expects a WebApplicationContext, an extension of a plain
ApplicationContext, for its own configuration. WebApplicationContext has a link to the
ServletContext and Servlet it is associated with. It is also bound to the ServletContext
such that applications can use static methods on RequestContextUtils to look up the
WebApplicationContext if they need access to it.
For many applications having a single WebApplicationContext is simple and sufficient.
It is also possible to have a context hierarchy where one root WebApplicationContext
is shared across multiple DispatcherServlet (or other Servlet) instances, each with
its own child WebApplicationContext configuration.
See Additional Capabilities of the ApplicationContext
for more on the context hierarchy feature.
The root WebApplicationContext typically contains infrastructure beans such as data repositories and
business services that need to be shared across multiple Servlet instances. Those beans
are effectively inherited and could be overridden (i.e. re-declared) in the Servlet-specific,
child WebApplicationContext which typically contains beans local to the given Servlet:
Below is example configuration with a WebApplicationContext hierarchy:
public class MyWebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
@Override
protected Class<?>[] getRootConfigClasses() {
return new Class<?>[] { RootConfig.class };
}
@Override
protected Class<?>[] getServletConfigClasses() {
return new Class<?>[] { App1Config.class };
}
@Override
protected String[] getServletMappings() {
return new String[] { "/app1/*" };
}
}|
Tip
|
If an application context hierarchy is not required, applications may return all
configuration via |
And the web.xml equivalent:
<web-app>
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/root-context.xml</param-value>
</context-param>
<servlet>
<servlet-name>app1</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/app1-context.xml</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>app1</servlet-name>
<url-pattern>/app1/*</url-pattern>
</servlet-mapping>
</web-app>|
Tip
|
If an application context hierarchy is not required, applications may configure a
"root" context only and leave the |
The DispatcherServlet delegates to special beans to process requests and render the
appropriate responses. By "special beans" we mean Spring-managed, Object instances that
implement WebFlux framework contracts. Those usually come with built-in contracts but
you can customize their properties, extend or replace them.
The table below lists the special beans detected by the DispatcherHandler:
| Bean type | Explanation |
|---|---|
Map a request to a handler along with a list of
interceptors for pre- and post-processing.
The mapping is based on some criteria the details of which vary by The two main |
|
HandlerAdapter |
Help the |
Strategy to resolve exceptions possibly mapping them to handlers, or to HTML error views, or other. See Exceptions. |
|
Resolve logical String-based view names returned from a handler to an actual |
|
Resolve the |
|
Resolve themes your web application can use, for example, to offer personalized layouts. See Themes. |
|
Abstraction for parsing a multi-part request (e.g. browser form file upload) with the help of some multipart parsing library. See Multipart resolver. |
|
Store and retrieve the "input" and the "output" |
Applications can declare the infrastructure beans listed in Special Bean Types
that are required to process requests. The DispatcherServlet checks the
WebApplicationContext for each special bean. If there are no matching bean types,
it falls back on the default types listed in
DispatcherServlet.properties.
In most cases the MVC Config is the best starting point. It declares the required beans in either Java or XML, and provides a higher level configuration callback API to customize it.
|
Note
|
Spring Boot relies on the MVC Java config to configure Spring MVC and also provides many extra convenient options. |
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.
This is recommended for applications that use Java-based Spring 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[] { "/" };
}
}If using XML-based Spring configuration, you should 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.
The DispatcherServlet processes requests as follows:
-
The
WebApplicationContextis 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 keyDispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE. -
The locale resolver is bound to the request to enable elements in the process to resolve the locale to use when processing the request (rendering the view, preparing data, and so on). If you do not need locale resolving, you do not need it.
-
The theme resolver is bound to the request to let elements such as views determine which theme to use. If you do not use themes, you can ignore it.
-
If you specify a multipart file resolver, the request is inspected for multiparts; if multiparts are found, the request is wrapped in a
MultipartHttpServletRequestfor further processing by other elements in the process. See Multipart resolver for further information about multipart handling. -
An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) is executed in order to prepare a model or rendering. Or alternatively for annotated controllers, the response may be rendered (within the
HandlerAdapter) instead of returning a view. -
If a model is returned, the view is rendered. If no model is returned, (may be due to a preprocessor or postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because the request could already have been fulfilled.
The HandlerExceptionResolver beans declared in the WebApplicationContext are used to
resolve exceptions thrown during request processing. Those exception resolvers allow
customizing the logic to address exceptions. See Exceptions for more details.
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.
| Parameter | Explanation |
|---|---|
|
Class that implements |
|
String that is passed to the context instance (specified by |
|
Namespace of the |
All HandlerMapping implementations supports handler interceptors that are useful when
you want to apply specific functionality to certain requests, for example, checking for
a principal. Interceptors must implement HandlerInterceptor from the
org.springframework.web.servlet package with three methods that should provide enough
flexibility to do all kinds of pre-processing and post-processing:
-
preHandle(..)— before the actual handler is executed -
postHandle(..)— after the handler is executed -
afterCompletion(..)— after the complete request has finished
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.
See Interceptors in the section on MVC configuration for examples of how to
configure interceptors. You can also register them directly via setters on individual
HandlerMapping implementations.
Note that postHandle is less useful with @ResponseBody and ResponseEntity methods for
which the response is written and committed within the HandlerAdapter and before
postHandle. That means its too late to make any changes to the response such as adding
an extra header. For such scenarios you can implement ResponseBodyAdvice and either
declare it as an Controller Advice bean or configure it directly on
RequestMappingHandlerAdapter.
If an exception occurs during request mapping or is thrown from a request handler such as
an @Controller, the DispatcherServlet delegates to a chain of HandlerExceptionResolver
beans to resolve the exception and provide alternative handling, which typically is an
error response.
The table below lists the available HandlerExceptionResolver implementations:
| HandlerExceptionResolver | Description |
|---|---|
|
A mapping between exception class names and error view names. Useful for rendering error pages in a browser application. |
{api-spring-framework}/web/servlet/mvc/support/DefaultHandlerExceptionResolver.html[DefaultHandlerExceptionResolver] |
Resolves exceptions raised by Spring MVC and maps them to HTTP status codes.
Also see alternative |
|
Resolves exceptions with the |
|
Resolves exceptions by invoking an |
You can form an exception resolver chain simply by declaring multiple HandlerExceptionResolver
beans in your Spring configuration and setting their order properties as needed.
The higher the order property, the later the exception resolver is positioned.
The contract of HandlerExceptionResolver specifies that it can return:
-
ModelAndViewthat points to an error view. -
Empty
ModelAndViewif the exception was handled within the resolver. -
nullif the exception remains unresolved, for subsequent resolvers to try; and if the exception remains at the end, it is allowed to bubble up to the Servlet container.
The MVC Config automatically declares built-in resolvers for default Spring MVC
exceptions, for @ResponseStatus annotated exceptions, and for support of
@ExceptionHandler methods. You can customize that list or replace it.
If an exception remains unresolved by any HandlerExceptionResolver and is therefore
left to propagate, or if the response status is set to an error status (i.e. 4xx, 5xx),
Servlet containers may render a default error page in HTML. To customize the default
error page of the container, you can declare an error page mapping in web.xml:
<error-page>
<location>/error</location>
</error-page>Given the above, when an exception bubbles up, or the response has an error status, the
Servlet container makes an ERROR dispatch within the container to the configured URL
(e.g. "/error"). This is then processed by the DispatcherServlet, possibly mapping it
to an @Controller which could be implemented to return an error view name with a model
or to render a JSON response as shown below:
@RestController
public class ErrorController {
@RequestMapping(path = "/error")
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;
}
}|
Tip
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The Servlet API does not provide a way to create error page mappings in Java. You can
however use both an |
Spring MVC defines the ViewResolver and View interfaces that enable you to render
models in a browser without tying you to a specific view technology. ViewResolver
provides a mapping between view names and actual views. View addresses the preparation
of data before handing over to a specific view technology.
The table below provides more details on the ViewResolver hierarchy:
| ViewResolver | Description |
|---|---|
|
Sub-classes of |
|
Implementation of |
|
Implementation of |
|
Simple implementation of the |
|
Convenient subclass of |
|
Convenient subclass of |
|
Implementation of the |
You chain view resolvers by declaring more than one resolver beans 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.
The contract of a ViewResolver specifies that it can return null to indicate the
view could not be found. However in the case of JSPs, and InternalResourceViewResolver,
the only way to figure out if a JSP exists is to perform a dispatch through
RequestDispatcher. Therefore an InternalResourceViewResolver must always be configured
to be last in the overall order of view resolvers.
To configure view resolution is as simple as adding ViewResolver beans to your Spring
configuration. The MVC Config provides provides a dedicated configuration API for
View Resolvers and also for adding logic-less
View Controllers which are useful for HTML template
rendering without controller logic.
The special redirect: prefix in a view name allows you to perform a redirect. The
UrlBasedViewResolver (and sub-classes) recognize this as an instruction that a
redirect is needed. The rest of the view name is 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.
Note that if a controller method is annotated with the @ResponseStatus, the annotation
value takes precedence over the response status set by RedirectView.
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 does a RequestDispatcher.forward().
Therefore, this prefix is not useful with InternalResourceViewResolver and
InternalResourceView (for JSPs) but it can be helpful if 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.
{api-spring-framework}/web/servlet/view/ContentNegotiatingViewResolver.html[ContentNegotiatingViewResolver]
does not resolve views itself but rather delegates
to other view resolvers, and selects the view that resembles the representation requested
by the client. The representation can be determined from the Accept header or from a
query parameter, e.g. "/path?format=pdf".
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.
See View Resolvers under MVC Config for configuration details.
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 Interception 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>| Property | Default | Description |
|---|---|---|
cookieName |
classname + LOCALE |
The name of the cookie |
cookieMaxAge |
Servlet container default |
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. In contrast to
CookieLocaleResolver, this strategy stores locally chosen locale settings in the
Servlet container’s HttpSession. As a consequence, those settings are just temporary
for each session and therefore lost when each session terminates.
Note that there is no direct relationship with external session management mechanisms
such as the Spring Session project. This SessionLocaleResolver will simply evaluate and
modify corresponding HttpSession attributes against the current HttpServletRequest.
You can enable changing of locales by adding the LocaleChangeInterceptor to one of the
handler mappings (see [mvc-handlermapping]). 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:
| 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.
MultipartResolver from the org.springframework.web.multipart package is a strategy
for parsing multipart requests including file uploads. There is one implementation
based on Commons FileUpload and another
based on Servlet 3.0 multipart request parsing.
To enable multipart handling, you need declare a MultipartResolver bean in your
DispatcherServlet Spring configuration with the name "multipartResolver".
The DispatcherServlet detects it and applies it to incoming request. When a POST with
content-type of "multipart/form-data" is received, the resolver parses the content and
wraps the current HttpServletRequest as MultipartHttpServletRequest in order to
provide access to resolved parts in addition to exposing them as request parameters.
To use Apache Commons FileUpload, simply configure a bean of type
CommonsMultipartResolver with the name multipartResolver. Of course you also need to
have commons-fileupload as a dependency on your classpath.
Servlet 3.0 multipart parsing needs to be enabled through Servlet container configuration:
-
in Java, set a
MultipartConfigElementon the Servlet registration. -
in
web.xml, add a"<multipart-config>"section to the servlet declaration.
public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
// ...
@Override
protected void customizeRegistration(ServletRegistration.Dynamic registration) {
// Optionally also set maxFileSize, maxRequestSize, fileSizeThreshold
registration.setMultipartConfig(new MultipartConfigElement("/tmp"));
}
}Once the Servlet 3.0 configuration is in place, simply add a bean of type
StandardServletMultipartResolver with the name multipartResolver.
The spring-web module provides some useful filters.
Browsers can only submit form data via HTTP GET or HTTP POST but non-browser clients can also
use HTTP PUT and PATCH. The Servlet API requires ServletRequest.getParameter*()
methods to support form field access only for HTTP POST.
The spring-web module provides HttpPutFormContentFilter that 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.
As a request goes through proxies such as load balancers the host, port, and scheme may change presenting a challenge for applications that need to create links to resources since the links should reflect the host, port, and scheme of the original request as seen from a client perspective.
RFC 7239 defines the "Forwarded" HTTP header for proxies to use to provide information about the original request. There are also other non-standard headers in use such as "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto".
ForwardedHeaderFilter detects, extracts, and uses information from the "Forwarded"
header, or from "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto".
It wraps the request in order to overlay its host, port, and scheme and also "hides"
the forwarded headers for subsequent processing.
Note that there are security considerations when using forwarded headers as explained in Section 8 of RFC 7239. At the application level it is difficult to determine whether forwarded headers can be trusted or not. This is why the network upstream should be configured correctly to filter out untrusted forwarded headers from the outside.
Applications that don’t have a proxy and don’t need to use forwarded headers can
configure the ForwardedHeaderFilter to remove and ignore such headers.
There is a ShallowEtagHeaderFilter. It is called shallow because it doesn’t have any
knowledge of the content. Instead it relies on buffering actual content written to the
response and computing the ETag value at the end.
See ETag Filter for more details.
Spring MVC provides fine-grained support for CORS configuration through annotations on
controllers. However when used with Spring Security it is advisable to rely on the built-in
CorsFilter that must be ordered ahead of Spring Security’s chain of filters.
See the section on [mvc-cors] and the [mvc-cors-filter] for more details.
Spring MVC provides an annotation-based programming model where @Controller and
@RestController components use annotations to express request mappings, request input,
exception handling, and more. Annotated controllers have flexible method signatures and
do not have to extend base classes nor implement specific interfaces.
@Controller
public class HelloController {
@GetMapping("/hello")
public String handle(Model model) {
model.addAttribute("message", "Hello World!");
return "index";
}
}In this particular example the method accepts a Model and returns a view name as a String
but many other options exist and are explained further below in this chapter.
|
Tip
|
Guides and tutorials on spring.io use the annotation-based programming model described in this section. |
You can define controller beans using a standard Spring bean definition in the
Servlet’s WebApplicationContext. The @Controller stereotype allows for auto-detection,
aligned with Spring general support for detecting @Component classes in the classpath
and auto-registering bean definitions for them. It also acts as a stereotype for the
annotated class, indicating its role as a web component.
To enable auto-detection of such @Controller beans, you can add component scanning to
your Java configuration:
@Configuration
@ComponentScan("org.example.web")
public class WebConfig {
// ...
}The XML configuration equivalent:
<?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.example.web"/>
<!-- ... -->
</beans>@RestController is a composed annotation that is
itself meta-annotated with @Controller and @ResponseBody indicating a controller whose
every method inherits the type-level @ResponseBody annotation and therefore writes
directly to the response body vs view resolution and rendering with an HTML template.
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"/>.
The @RequestMapping annotation is used to map requests to controllers methods. It has
various attributes to match by URL, HTTP method, request parameters, headers, and media
types. It can be used at the class-level to express shared mappings or at the method level
to narrow down to a specific endpoint mapping.
There are also HTTP method specific shortcut variants of @RequestMapping:
-
@GetMapping -
@PostMapping -
@PutMapping -
@DeleteMapping -
@PatchMapping
The above are Custom Annotations that are provided out of the box
because arguably most controller methods should be mapped to a specific HTTP method vs
using @RequestMapping which by default matches to all HTTP methods. At the same an
@RequestMapping is still needed at the class level to express shared mappings.
Below is an example with type and method level mappings:
@RestController
@RequestMapping("/persons")
class PersonController {
@GetMapping("/{id}")
public Person getPerson(@PathVariable Long id) {
// ...
}
@PostMapping
@ResponseStatus(HttpStatus.CREATED)
public void add(@RequestBody Person person) {
// ...
}
}You can map requests using glob patterns and wildcards:
-
?matches one character -
*matches zero or more characters within a path segment -
**match zero or more path segments
You can also declare URI variables and access their values with @PathVariable:
@GetMapping("/owners/{ownerId}/pets/{petId}")
public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) {
// ...
}URI variables can be declared at the class and method level:
@Controller
@RequestMapping("/owners/{ownerId}")
public class OwnerController {
@GetMapping("/pets/{petId}")
public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) {
// ...
}
}URI variables are automatically converted to the appropriate type or`TypeMismatchException`
is raised. Simple types — int, long, Date, are supported by default and you can
register support for any other data type.
See Type Conversion and DataBinder.
URI variables can be named explicitly — e.g. @PathVariable("customId"), but you can
leave that detail out if the names are the same and your code is compiled with debugging
information or with the -parameters compiler flag on Java 8.
The syntax {varName:regex} declares a URI variable with a regular expressions with the
syntax {varName:regex} — e.g. given URL "/spring-web-3.0.5 .jar", the below method
extracts the name, version, and file extension:
@GetMapping("/{name:[a-z-]+}-{version:\\d\\.\\d\\.\\d}{ext:\\.[a-z]+}")
public void handle(@PathVariable String version, @PathVariable String ext) {
// ...
}URI path patterns can also have embedded ${…} placeholders that are resolved on startup
via PropertyPlaceHolderConfigurer against local, system, environment, and other property
sources. This can be used for example to parameterize a base URL based on some external
configuration.
|
Note
|
Spring MVC uses the |
When multiple patterns match a URL, they must be compared to find the best match. This done
via AntPathMatcher.getPatternComparator(String path) which looks for patterns that more
specific.
A pattern is less specific if it has a lower count of URI variables and single wildcards counted as 1 and double wildcards counted as 2. Given an equal score, the longer pattern is chosen. Given the same score and length, the pattern with more URI variables than wildcards is chosen.
The default mapping pattern /** is excluded from scoring and always
sorted last. Also prefix patterns such as /public/** are considered less
specific than other pattern that don’t have double wildcards.
For the full details see AntPatternComparator in AntPathMatcher and also keep mind that
the PathMatcher implementation used can be customized. See Path Matching
in the configuration section.
By default Spring MVC performs ".*" suffix pattern matching so that a
controller mapped to /person is also implicitly mapped to /person.*.
The file extension is then used to interpret the requested content type to use for
the response (i.e. instead of the "Accept" header), e.g. /person.pdf,
/person.xml, etc.
Using file extensions like this was necessary when browsers used to send Accept headers that were hard to interpret consistently. At present that is no longer a necessity and using the "Accept" header should be the preferred choice.
Over time the use of file name extensions has proven problematic in a variety of ways. It can cause ambiguity when overlayed with the use of URI variables, path parameters, URI encoding, and it also makes it difficult to reason about URL-based authorization and security (see next section for more details).
To completely disable the use of file extensions, you must set both of these:
-
useSuffixPatternMatching(false), see PathMatchConfigurer -
favorPathExtension(false), see ContentNeogiationConfigurer
URL-based content negotiation can still be useful, for example when typing a URL in a
browser. To enable that we recommend a query parameter based strategy to avoid most of
the issues that come with file extensions. Or if you must use file extensions, consider
restricting them to a list of explicitly registered extensions through the
mediaTypes property of ContentNeogiationConfigurer.
Reflected file download (RFD) attack is similar to XSS in that it relies on request input, e.g. query parameter, URI variable, being reflected in the response. However instead of inserting JavaScript into HTML, an RFD attack relies on the browser switching to perform a download and treating the response as an executable script when double-clicked later.
In Spring MVC @ResponseBody and ResponseEntity methods are at risk because
they can render different content types which clients can request via URL path extensions.
Disabling suffix pattern matching and the use of path extensions for content negotiation
lower the risk but are not sufficient to prevent RFD attacks.
To prevent RFD attacks, prior to rendering the response body Spring MVC adds a
Content-Disposition:inline;filename=f.txt header to suggest a fixed and safe download
file. This is done only if the URL path contains a file extension that is neither whitelisted
nor explicitly registered for content negotiation purposes. However it may potentially have
side effects when URLs are typed directly into a browser.
Many common path extensions are whitelisted by default. Applications with custom
HttpMessageConverter implementations can explicitly register file extensions for content
negotiation to avoid having a Content-Disposition header added for those extensions.
See Content Types.
Check CVE-2015-5211 for additional recommendations related to RFD.
You can narrow the request mapping based on the Content-Type of the request:
@PostMapping(path = "/pets", consumes = "application/json")
public void addPet(@RequestBody Pet pet) {
// ...
}The consumes attribute also supports negation expressions — e.g. !text/plain means any
content type other than "text/plain".
You can declare a shared consumes attribute at the class level. Unlike most other request mapping attributes however when used at the class level, a method-level consumes attribute will overrides rather than extend the class level declaration.
|
Tip
|
|
You can narrow the request mapping based on the Accept request header and the list of
content types that a controller method produces:
@GetMapping(path = "/pets/{petId}", produces = "application/json;charset=UTF-8")
@ResponseBody
public Pet getPet(@PathVariable String petId) {
// ...
}The media type can specify a character set. Negated expressions are supported — e.g.
!text/plain means any content type other than "text/plain".
You can declare a shared produces attribute at the class level. Unlike most other request mapping attributes however when used at the class level, a method-level produces attribute will overrides rather than extend the class level declaration.
|
Tip
|
|
You can narrow request mappings based on request parameter conditions. You can test for the
presence of a request parameter ("myParam"), for the absence ("!myParam"), or for a
specific value ("myParam=myValue"):
@GetMapping(path = "/pets/{petId}", params = "myParam=myValue")
public void findPet(@PathVariable String petId) {
// ...
}You can also use the same with request header conditions:
@GetMapping(path = "/pets", headers = "myHeader=myValue")
public void findPet(@PathVariable String petId) {
// ...
}@GetMapping — and also @RequestMapping(method=HttpMethod.GET), support HTTP HEAD
transparently for request mapping purposes. Controller methods don’t need to change.
A response wrapper, applied in javax.servlet.http.HttpServlet, ensures a "Content-Length"
header is set to the number of bytes written and without actually writing to the response.
@GetMapping — and also @RequestMapping(method=HttpMethod.GET), are implicitly mapped to
and also support HTTP HEAD. An HTTP HEAD request is processed as if it were HTTP GET except
but instead of writing the body, the number of bytes are counted and the "Content-Length"
header set.
By default HTTP OPTIONS is handled by setting the "Allow" response header to the list of HTTP
methods listed in all @RequestMapping methods with matching URL patterns.
For a @RequestMapping without HTTP method declarations, the "Allow" header is set to
"GET,HEAD,POST,PUT,PATCH,DELETE,OPTIONS". Controller methods should always declare the
supported HTTP methods for example by using the HTTP method specific variants — @GetMapping, @PostMapping, etc.
@RequestMapping method can be explicitly mapped to HTTP HEAD and HTTP OPTIONS, but that
is not necessary in the common case.
Spring MVC supports the use of composed annotations
for request mapping. Those are annotations that are themselves meta-annotated with
@RequestMapping and composed to redeclare a subset (or all) of the @RequestMapping
attributes with a narrower, more specific purpose.
@GetMapping, @PostMapping, @PutMapping, @DeleteMapping, and @PatchMapping are
examples of composed annotations. They’re provided out of the box because arguably most
controller methods should be mapped to a specific HTTP method vs using @RequestMapping
which by default matches to all HTTP methods. If you need an example of composed
annotations, look at how those are declared.
Spring MVC also supports custom request mapping attributes with custom request matching
logic. This is a more advanced option that requires sub-classing
RequestMappingHandlerMapping and overriding the getCustomMethodCondition method where
you can check the custom attribute and return your own RequestCondition.
@RequestMapping handler methods have a flexible signature and can choose from a range of
supported controller method arguments and return values.
The table below shows supported controller method arguments. Reactive types are not supported for any arguments.
JDK 8’s java.util.Optional is supported as a method argument in combination with
annotations that have a required attribute — e.g. @RequestParam, @RequestHeader,
etc, and is equivalent to required=false.
| Controller method argument | Description |
|---|---|
|
Generic access to request parameters, request & session attributes, without direct use of the Servlet API. |
|
Choose any specific request or response type — e.g. |
|
Enforces the presence of a session. As a consequence, such an argument is never |
|
Servlet 4.0 push builder API for programmatic HTTP/2 resource pushes.
Note that per Servlet spec, the injected |
|
Currently authenticated user; possibly a specific |
|
The HTTP method of the request. |
|
The current request locale, determined by the most specific |
|
The time zone associated with the current request, as determined by a |
|
For access to the raw request body as exposed by the Servlet API. |
|
For access to the raw response body as exposed by the Servlet API. |
|
For access to URI template variables. See URI patterns. |
|
For access to name-value pairs in URI path segments. See Matrix variables. |
|
For access to Servlet request parameters. Parameter values are converted to the declared method argument type. See @RequestParam. Note that use of |
|
For access to request headers. Header values are converted to the declared method argument type. See @RequestHeader. |
|
For access to cookies. Cookies values are converted to the declared method argument type. See @CookieValue. |
|
For access to the HTTP request body. Body content is converted to the declared method
argument type using |
|
For access to request headers and body. The body is converted with |
|
For access to a part in a "multipart/form-data" request. See Multipart. |
|
For access to the model that is used in HTML controllers and exposed to templates as part of view rendering. |
|
Specify attributes to use in case of a redirect — i.e. to be appended to the query string, and/or flash attributes to be stored temporarily until the request after redirect. See Redirect attributes and Flash attributes. |
|
For access to an existing attribute in the model (instantiated if not present) with data binding and validation applied. See @ModelAttribute as well as Model and DataBinder. Note that use of |
|
For access to errors from validation and data binding for a command object
(i.e. |
|
For marking form processing complete which triggers cleanup of session attributes
declared through a class-level |
|
For preparing a URL relative to the current request’s host, port, scheme, context path, and
the literal part of the servlet mapping also taking into account |
|
For access to any session attribute; in contrast to model attributes stored in the session
as a result of a class-level |
|
For access to request attributes. See @RequestAttribute for more details. |
Any other argument |
If a method argument is not matched to any of the above, by default it is resolved as
an |
The table below shows supported controller method return values. Reactive types are supported for all return values, see below for more details.
| Controller method return value | Description |
|---|---|
|
The return value is converted through |
|
The return value specifies the full response including HTTP headers and body be converted
through |
|
For returning a response with headers and no body. |
|
A view name to be resolved with |
|
A |
|
Attributes to be added to the implicit model with the view name implicitly determined
through a |
|
An attribute to be added to the model with the view name implicitly determined through
a Note that |
|
The view and model attributes to use, and optionally a response status. |
|
A method with a If none of the above is true, a |
|
Produce any of the above return values asynchronously from any thread — e.g. possibly as a
result of some event or callback. See Async Requests and
|
|
Produce any of the above return values asynchronously in a Spring MVC managed thread.
See Async Requests and |
|
Alternative to |
|
Emit a stream of objects asynchronously to be written to the response with
|
|
Write to the response |
Reactive types — Reactor, RxJava, or others via |
Alternative to For streaming scenarios — e.g. See Async Requests and Reactive types. |
Any other return value |
If a return value is not matched to any of the above, by default it is treated as a view
name, if it is |
Some annotated controller method arguments that represent String-based request input — e.g.
@RequestParam, @RequestHeader, @PathVariable, @MatrixVariable, and @CookieValue,
may require type conversion if the argument is declared as something other than String.
For such cases type conversion is automatically applied based on the configured converters.
By default simple types such as int, long, Date, etc. are supported. Type conversion
can be customized through a WebDataBinder, see DataBinder, or by registering
Formatters with the FormattingConversionService, see
Spring Field Formatting.
RFC 3986 discusses name-value pairs in path segments. In Spring MVC we refer to those as "matrix variables" based on an "old post" by Tim Berners-Lee but they can be also be referred to as URI path parameters.
Matrix variables can appear in any path segment, each variable separated by semicolon and
multiple values separated by comma, e.g. "/cars;color=red,green;year=2012". Multiple
values can also be specified through repeated variable names, e.g.
"color=red;color=green;color=blue".
If a URL is expected to contain matrix variables, the request mapping for a controller method must use a URI variable to mask that variable content and ensure the request can be matched successfully independent of matrix variable order and presence. Below is an example:
// GET /pets/42;q=11;r=22
@GetMapping("/pets/{petId}")
public void findPet(@PathVariable String petId, @MatrixVariable int q) {
// petId == 42
// q == 11
}Given that all path segments may contain matrix variables, sometimes you may need to disambiguate which path variable the matrix variable is expected to be in. For example:
// GET /owners/42;q=11/pets/21;q=22
@GetMapping("/owners/{ownerId}/pets/{petId}")
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
@GetMapping("/pets/{petId}")
public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) {
// q == 1
}To get all matrix variables, use a MultiValueMap:
// GET /owners/42;q=11;r=12/pets/21;q=22;s=23
@GetMapping("/owners/{ownerId}/pets/{petId}")
public void findPet(
@MatrixVariable MultiValueMap<String, String> matrixVars,
@MatrixVariable(pathVar="petId"") MultiValueMap<String, String> petMatrixVars) {
// matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]
// petMatrixVars: ["q" : 22, "s" : 23]
}Note that you need to enable the use of matrix variables. In the MVC Java config you need
to set a UrlPathHelper with removeSemicolonContent=false via
Path Matching. In the MVC XML namespace, use
<mvc:annotation-driven enable-matrix-variables="true"/>.
Use the @RequestParam annotation to bind Servlet request parameters (i.e. query
parameters or form data) to a method argument in a controller.
The following code snippet shows the usage:
@Controller
@RequestMapping("/pets")
public class EditPetForm {
// ...
@GetMapping
public String setupForm(@RequestParam("petId") int petId, Model model) {
Pet pet = this.clinic.loadPet(petId);
model.addAttribute("pet", pet);
return "petForm";
}
// ...
}Method parameters using this annotation are required by default, but you can specify that
a method parameter is optional by setting @RequestParam's required flag to false
or by declaring the argument with an java.util.Optional wrapper.
Type conversion is applied automatically if the target method parameter type is not
String. See Type Conversion.
When an @RequestParam annotation is declared as Map<String, String> or
MultiValueMap<String, String> argument, the map is populated with all request
parameters.
Note that use of @RequestParam is optional, e.g. to set its attributes.
By default any argument that is a simple value type, as determined by
{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty],
and is not resolved by any other argument resolver, is treated as if it was annotated
with @RequestParam.
Use the @RequestHeader annotation to bind a request header to a method argument in a
controller.
Given request with headers:
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 gets the value of the Accept-Encoding and Keep-Alive headers:
@GetMapping("/demo")
public void handle(
@RequestHeader("Accept-Encoding") String encoding,
@RequestHeader("Keep-Alive") long keepAlive) {
//...
}Type conversion is applied automatically if the target method parameter type is not
String. See 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 |
Use the @CookieValue annotation to bind the value of an HTTP cookie to a method argument
in a controller.
Given request with the following cookie:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
The following code sample demonstrates how to get the cookie value:
@GetMapping("/demo")
public void handle(@CookieValue("JSESSIONID") String cookie) {
//...
}Type conversion is applied automatically if the target method parameter type is not
String. See Type Conversion.
Use the @ModelAttribute annotation on a method argument to access an attribute from the
model, or have it instantiated if not present. The model attribute is also overlaid with
values from HTTP Servlet request parameters whose names match to field names. This is
referred to as data binding and it saves you from having to deal with parsing and
converting individual query parameters and form fields. For example:
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute Pet pet) { }The Pet instance above is resolved as follows:
-
From the model if already added via Model.
-
From the HTTP session via @SessionAttributes.
-
From a URI path variable passed through a
Converter(example below). -
From the invocation of a default constructor.
-
From the invocation of a "primary constructor" with arguments matching to Servlet request parameters; argument names are determined via JavaBeans
@ConstructorPropertiesor via runtime-retained parameter names in the bytecode.
While it is common to use a Model to populate the model with
attributes, one other alternative is to rely on a Converter<String, T> in combination
with a URI path variable convention. In the example below the model attribute name
"account" matches the URI path variable "account" and the Account is loaded by passing
the String account number through a registered Converter<String, Account>:
@PutMapping("/accounts/{account}")
public String save(@ModelAttribute("account") Account account) {
// ...
}After the model attribute instance is obtained, data binding is applied. The
WebDataBinder class matches Servlet request parameter names (query parameters and form
fields) to field names on the target Object. Matching fields are populated after type
conversion is applied where necessary. For more on data binding (and validation) see
Validation. For more on customizing data binding see
DataBinder.
Data binding may result in errors. By default a BindException is raised but to check
for such errors in the controller method, add a BindingResult argument immediately next
to the @ModelAttribute as shown below:
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {
if (result.hasErrors()) {
return "petForm";
}
// ...
}In some cases you may want access to a model attribute without data binding. For such
cases you can inject the Model into the controller and access it directly or
alternatively set @ModelAttribute(binding=false) as shown below:
@ModelAttribute
public AccountForm setUpForm() {
return new AccountForm();
}
@ModelAttribute
public Account findAccount(@PathVariable String accountId) {
return accountRepository.findOne(accountId);
}
@PostMapping("update")
public String update(@Valid AccountUpdateForm form, BindingResult result,
@ModelAttribute(binding=false) Account account) {
// ...
}Validation can be applied automatically after data binding by adding the
javax.validation.Valid annotation or Spring’s @Validated annotation (also see
Bean validation and
Spring validation). For example:
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) {
if (result.hasErrors()) {
return "petForm";
}
// ...
}Note that use of @ModelAttribute is optional, e.g. to set its attributes.
By default any argument that is not a simple value type, as determined by
{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty],
and is not resolved by any other argument resolver, is treated as if it was annotated
with @ModelAttribute.
@SessionAttributes is used to store model attributes in the HTTP Servlet session between
requests. It is a type-level annotation that declares session attributes used by a
specific controller. This will typically list the names of model attributes or types of
model attributes which should be transparently stored in the session for subsequent
requests to access.
For example:
@Controller
@SessionAttributes("pet")
public class EditPetForm {
// ...
}On the first request when a model attribute with the name "pet" is added to the model,
it is automatically promoted to and saved in the HTTP Servlet session. It remains there
until another controller method uses a SessionStatus method argument to clear the
storage:
@Controller
@SessionAttributes("pet")
public class EditPetForm {
// ...
@PostMapping("/pets/{id}")
public String handle(Pet pet, BindingResult errors, SessionStatus status) {
if (errors.hasErrors) {
// ...
}
status.setComplete();
// ...
}
}
}If you need access to pre-existing session attributes that are managed globally,
i.e. outside the controller (e.g. by a filter), and may or may not be present
use the @SessionAttribute annotation on a method parameter:
@RequestMapping("/")
public String handle(@SessionAttribute User user) {
// ...
}For use cases that require adding or removing session attributes consider injecting
org.springframework.web.context.request.WebRequest or
javax.servlet.http.HttpSession into the controller method.
For temporary storage of model attributes in the session as part of a controller
workflow consider using SessionAttributes as described in
@SessionAttributes.
Similar to @SessionAttribute the @RequestAttribute annotation can be used to
access pre-existing request attributes created earlier, e.g. by a Servlet Filter
or HandlerInterceptor:
@GetMapping("/")
public String handle(@RequestAttribute Client client) {
// ...
}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:
@PostMapping("/files/{path}")
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 Flash attributes for more information.
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.
The concept of flash attributes exists in many other Web frameworks and has proven to be exposed sometimes to concurrency issues. This is because by definition flash attributes are to be stored until the next request. However the very "next" request may not be the intended recipient but another asynchronous request (e.g. polling or resource requests) in which case the flash attributes are removed too early.
To reduce the possibility of such issues, RedirectView automatically "stamps"
FlashMap instances with the path and query parameters of the target redirect URL. In
turn the default FlashMapManager matches that information to incoming requests when
looking up the "input" FlashMap.
This does not eliminate the possibility of a concurrency issue entirely but nevertheless reduces it greatly with information that is already available in the redirect URL. Therefore the use of flash attributes is recommended mainly for redirect scenarios .
After a MultipartResolver has been enabled, the content of POST
requests with "multipart/form-data" is parsed and accessible as regular request
parameters. In the example below we access one regular form field and one uploaded
file:
@Controller
public class FileUploadController {
@PostMapping("/form")
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
|
When using Servlet 3.0 multipart parsing you can also use |
Multipart content can also be used as part of data binding to a command object. For example the above form field and file could have been fields on a form object:
class MyForm {
private String name;
private MultipartFile file;
// ...
}
@Controller
public class FileUploadController {
@PostMapping("/form")
public String handleFormUpload(MyForm form, BindingResult errors) {
if (!form.getFile().isEmpty()) {
byte[] bytes = form.getFile().getBytes();
// store the bytes somewhere
return "redirect:uploadSuccess";
}
return "redirect:uploadFailure";
}
}Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. For example a file along with JSON:
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 can access the "meta-data" part with @RequestParam as a String but you’ll
probably want it deserialized from JSON (similar to @RequestBody). Use the
@RequestPart annotation to access a multipart after converting it with an
HttpMessageConverter:
@PostMapping("/")
public String handle(@RequestPart("meta-data") MetaData metadata,
@RequestPart("file-data") MultipartFile file) {
// ...
}@RequestPart can be used in combination with javax.validation.Valid, or Spring’s
@Validated annotation, which causes Standard Bean Validation to be applied.
By default validation errors cause a MethodArgumentNotValidException which is turned
into a 400 (BAD_REQUEST) response. Alternatively validation errors can be handled locally
within the controller through an Errors or BindingResult argument:
@PostMapping("/")
public String handle(@Valid @RequestPart("meta-data") MetaData metadata,
BindingResult result) {
// ...
}Use the @RequestBody annotation to have the request body read and deserialized into an
Object through an HttpMessageConverter.
Below is an example with an @RequestBody argument:
@PostMapping("/accounts")
public void handle(@RequestBody Account account) {
// ...
}You can use the Message Converters option of the MVC Config to configure or customize message conversion.
@RequestBody can be used in combination with javax.validation.Valid, or Spring’s
@Validated annotation, which causes Standard Bean Validation to be applied.
By default validation errors cause a MethodArgumentNotValidException which is turned
into a 400 (BAD_REQUEST) response. Alternatively validation errors can be handled locally
within the controller through an Errors or BindingResult argument:
@PostMapping("/accounts")
public void handle(@Valid @RequestBody Account account, BindingResult result) {
// ...
}HttpEntity is more or less identical to using @RequestBody but based on a
container object that exposes request headers and body. Below is an example:
@PostMapping("/accounts")
public void handle(HttpEntity<Account> entity) {
// ...
}Use the @ResponseBody annotation on a method to have the return serialized to the
response body through an
HttpMessageConverter. For example:
@GetMapping("/accounts/{id}")
@ResponseBody
public Account handle() {
// ...
}@ResponseBody is also supported at the class level in which case it is inherited by
all controller methods. This is the effect of @RestController which is nothing more
than a meta-annotation marked with @Controller and @ResponseBody.
@ResponseBody may be used with reactive types.
See Async Requests and Reactive types for more details.
You can use the Message Converters option of the MVC Config to configure or customize message conversion.
@ResponseBody methods can be combined with JSON serialization views.
See Jackson JSON for details.
ResponseEntity is more or less identical to using @ResponseBody but based
on a container object that specifies request headers and body. Below is an example:
@PostMapping("/something")
public ResponseEntity<String> handle() {
// ...
URI location = ... ;
return ResponseEntity.created(location).build();
}Spring MVC provides built-in support for
Jackson’s Serialization Views
which allows rendering only a subset of all fields in an Object. To use it with
@ResponseBody or ResponseEntity controller methods, use Jackson’s
@JsonView annotation to activate a serialization view class:
@RestController
public class UserController {
@GetMapping("/user")
@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
|
|
For controllers relying on view resolution, simply add the serialization view class to the model:
@Controller
public class UserController extends AbstractController {
@GetMapping("/user")
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.
The @ModelAttribute annotation can be used:
-
On a method argument in
@RequestMappingmethods to create or access an Object from the model, and to bind it to the request through aWebDataBinder. -
As a method-level annotation in
@Controlleror@ControllerAdviceclasses helping to initialize the model prior to any@RequestMappingmethod invocation. -
On a
@RequestMappingmethod to mark its return value is a model attribute.
This section discusses @ModelAttribute methods, or the 2nd from the list above.
A controller can have any number of @ModelAttribute methods. All such methods are
invoked before @RequestMapping methods in the same controller. A @ModelAttribute
method can also be shared across controllers via @ControllerAdvice. See the section on
Controller Advice for more details.
@ModelAttribute methods have flexible method signatures. They support many of the same
arguments as @RequestMapping methods except for @ModelAttribute itself nor anything
related to the request body.
An example @ModelAttribute method:
@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
model.addAttribute(accountRepository.findAccount(number));
// add more ...
}To add one attribute only:
@ModelAttribute
public Account addAccount(@RequestParam String number) {
return accountRepository.findAccount(number);
}|
Note
|
When a name is not explicitly specified, a default name is chosen based on the Object
type as explained in the Javadoc for
{api-spring-framework}/core/Conventions.html[Conventions].
You can always assign an explicit name by using the overloaded |
@ModelAttribute can also be used as a method-level annotation on @RequestMapping
methods in which case the return value of the @RequestMapping method is interpreted as a
model attribute. This is typically not required, as it is the default behavior in HTML
controllers, unless the return value is a String which would otherwise be interpreted
as a view name (also see [mvc-coc-r2vnt]). @ModelAttribute can also help to customize
the model attribute name:
@GetMapping("/accounts/{id}")
@ModelAttribute("myAccount")
public Account handle() {
// ...
return account;
}@Controller or @ControllerAdvice classes can have @InitBinder methods in order to
initialize instances of WebDataBinder, and those in turn are used to:
-
Bind request parameters (i.e. form data or query) to a model object.
-
Convert String-based request values such as request parameters, path variables, headers, cookies, and others, to the target type of controller method arguments.
-
Format model object values as String values when rendering HTML forms.
@InitBinder methods can register controller-specific java.bean.PropertyEditor, or
Spring Converter and Formatter components. In addition, the
MVC config can be used to register Converter and Formatter
types in a globally shared FormattingConversionService.
@InitBinder methods support many of the same arguments that a @RequestMapping methods
do, except for @ModelAttribute (command object) arguments. Typically they’re are declared
with a WebDataBinder argument, for registrations, and a void return value.
Below is an example:
@Controller
public class FormController {
@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 when using a Formatter-based setup through a shared
FormattingConversionService, you could re-use the same approach and register
controller-specific Formatter's:
@Controller
public class FormController {
@InitBinder
protected void initBinder(WebDataBinder binder) {
binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd"));
}
// ...
}@Controller and @ControllerAdvice classes can have
@ExceptionHandler methods to handle exceptions from controller methods. For example:
@Controller
public class SimpleController {
// ...
@ExceptionHandler
public ResponseEntity<String> handle(IOException ex) {
// ...
}
}The annotation can list the exception types to match. Or simply declare the target
exception as a method argument as shown above. When multiple exception methods match,
a root exception match is generally preferred to a cause exception match. More formally
the ExceptionDepthComparator is used to sort exceptions based on their depth from the
thrown exception type.
In a multi-@ControllerAdvice arrangement, please declare your primary root exception
mappings on a @ControllerAdvice prioritized with a corresponding order. While a root
exception match is preferred to a cause, this is mainly among the methods of a given
controller or @ControllerAdvice. That means a cause match on a higher-priority
@ControllerAdvice is preferred to any match (e.g. root) on a lower-priority
@ControllerAdvice.
Support for @ExceptionHandler methods in Spring MVC is built on the DispatcherServlet
level, HandlerExceptionResolver mechanism.
@ExceptionHandler methods support the following arguments:
| Method argument | Description |
|---|---|
Exception type |
For access to the raised exception. |
|
For access to the controller method that raised the exception. |
|
Generic access to request parameters, request & session attributes, without direct use of the Servlet API. |
|
Choose any specific request or response type — e.g. |
|
Enforces the presence of a session. As a consequence, such an argument is never |
|
Currently authenticated user; possibly a specific |
|
The HTTP method of the request. |
|
The current request locale, determined by the most specific |
|
The time zone associated with the current request, as determined by a |
|
For access to the raw response body as exposed by the Servlet API. |
|
For access to the model for an error response, always empty. |
|
Specify attributes to use in case of a redirect — i.e. to be appended to the query string, and/or flash attributes to be stored temporarily until the request after redirect. See Redirect attributes and Flash attributes. |
|
For access to any session attribute; in contrast to model attributes stored in the session
as a result of a class-level |
|
For access to request attributes. See @RequestAttribute for more details. |
@ExceptionHandler methods support the following return values:
| Return value | Description |
|---|---|
|
The return value is converted through |
|
The return value specifies the full response including HTTP headers and body be converted
through |
|
A view name to be resolved with |
|
A |
|
Attributes to be added to the implicit model with the view name implicitly determined
through a |
|
An attribute to be added to the model with the view name implicitly determined through
a Note that |
|
The view and model attributes to use, and optionally a response status. |
|
A method with a If none of the above is true, a |
Any other return value |
If a return value is not matched to any of the above, by default it is treated as a model attribute to be added to the model, unless it is a simple type, as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty] in which case it remains unresolved. |
A common requirement for REST services is to include error details in the body of the
response. The Spring Framework does not automatically do this because the representation
of error details in the response body is application specific. However a
@RestController may use @ExceptionHandler methods with a ResponseEntity return
value to set the status and the body of the response. Such methods may also be declared
in @ControllerAdvice classes to apply them globally.
Applications that implement global exception handling with error details in the response
body should consider extending
{api-spring-framework}/web/servlet/mvc/method/annotation/ResponseEntityExceptionHandler.html[ResponseEntityExceptionHandler]
which provides handling for exceptions that Spring MVC raises along with hooks to
customize the response body. To make use of this, create a sub-class of
ResponseEntityExceptionHandler, annotate with @ControllerAdvice, override the
necessary methods, and declare it as a Spring bean.
Typically @ExceptionHandler, @InitBinder, and @ModelAttribute methods apply within
the @Controller class (or class hierarchy) they are declared in. If you want such
methods to apply more globally, across controllers, you can declare them in a class
marked with @ControllerAdvice or @RestControllerAdvice.
@ControllerAdvice is marked with @Component which means such classes can be registered
as Spring beans via component scanning.
@RestControllerAdvice is also a meta-annotation marked with both @ControllerAdvice and
@ResponseBody which essentially means @ExceptionHandler methods are rendered to the
response body via message conversion (vs view resolution/template rendering).
On startup, the infrastructure classes for @RequestMapping and @ExceptionHandler methods
detect Spring beans of type @ControllerAdvice, and then apply their methods at runtime.
Global @ExceptionHandler methods (from an @ControllerAdvice) are applied after local
ones (from the @Controller). By contrast global @ModelAttribute and @InitBinder
methods are applied before local ones.
By default @ControllerAdvice methods apply to every request, i.e. all controllers, but
you can narrow that down to a subset of controllers via attributes on the annotation:
// Target all Controllers annotated with @RestController
@ControllerAdvice(annotations = RestController.class)
public class ExampleAdvice1 {}
// Target all Controllers within specific packages
@ControllerAdvice("org.example.controllers")
public class ExampleAdvice2 {}
// Target all Controllers assignable to specific classes
@ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class})
public class ExampleAdvice3 {}Keep in mind the above selectors are evaluated at runtime and may negatively impact performance if used extensively. See the {api-spring-framework}/web/bind/annotation/ControllerAdvice.html[@ControllerAdvice] Javadoc for more details.
This section describes various options available in the Spring Framework to prepare URIs.
You can use ServletUriComponentsBuilder to create URIs relative to the current request:
HttpServletRequest request = ...
// Re-uses host, scheme, port, path and query string...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request)
.replaceQueryParam("accountId", "{id}").build()
.expand("123")
.encode();You can create URIs relative to the context path:
// Re-uses host, port and context path...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request)
.path("/accounts").build()You can create URIs relative to a Servlet (e.g. /main/*):
// Re-uses host, port, context path, and Servlet prefix...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request)
.path("/accounts").build()|
Caution
|
|
Spring MVC provides a mechanism to prepare links to controller methods. For example:
@Controller
@RequestMapping("/hotels/{hotel}")
public class BookingController {
@GetMapping("/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();|
Caution
|
|
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.
Spring MVC has an extensive integration with Servlet 3.0 asynchronous request processing:
-
DeferredResultandCallablereturn values in controller method provide basic support for a single asynchronous return value. -
Controllers can stream multiple values including SSE and raw data.
-
Controllers can use reactive clients and return reactive types for response handling.
Once the asynchronous request processing feature is
enabled in the Servlet container, controller methods can
wrap any supported controller method return value with DeferredResult:
@GetMapping("/quotes")
@ResponseBody
public DeferredResult<String> quotes() {
DeferredResult<String> deferredResult = new DeferredResult<String>();
// Save the deferredResult somewhere..
return deferredResult;
}
// From some other thread...
deferredResult.setResult(data);The controller can produce the return value asynchronously, from a different thread, for example in response to an external event (JMS message), a scheduled task, or other.
A controller may also wrap any supported return value with java.util.concurrent.Callable:
@PostMapping
public Callable<String> processUpload(final MultipartFile file) {
return new Callable<String>() {
public String call() throws Exception {
// ...
return "someView";
}
};
}The return value will then be obtained by executing the the given task through the
configured TaskExecutor.
Here is a very concise overview of Servlet asynchronous request processing:
-
A
ServletRequestcan be put in asynchronous mode by callingrequest.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. -
The call to
request.startAsync()returnsAsyncContextwhich can be used for further control over async processing. For example it provides the methoddispatch, that is similar to a forward from the Servlet API except it allows an application to resume request processing on a Servlet container thread. -
The
ServletRequestprovides access to the currentDispatcherTypethat can be used to distinguish between processing the initial request, an async dispatch, a forward, and other dispatcher types.
DeferredResult processing:
-
Controller returns a
DeferredResultand saves it in some in-memory queue or list where it can be accessed. -
Spring MVC calls
request.startAsync(). -
Meanwhile the
DispatcherServletand all configured Filter’s exit the request processing thread but the response remains open. -
The application sets the
DeferredResultfrom some thread and Spring MVC dispatches the request back to the Servlet container. -
The
DispatcherServletis invoked again and processing resumes with the asynchronously produced return value.
Callable processing:
-
Controller returns a
Callable. -
Spring MVC calls
request.startAsync()and submits theCallableto aTaskExecutorfor processing in a separate thread. -
Meanwhile the
DispatcherServletand all Filter’s exit the Servlet container thread but the response remains open. -
Eventually the
Callableproduces a result and Spring MVC dispatches the request back to the Servlet container to complete processing. -
The
DispatcherServletis invoked again and processing resumes with the asynchronously produced return value from theCallable.
For further background and context you can also read the blog posts that introduced asynchronous request processing support in Spring MVC 3.2.
When using a DeferredResult you can choose whether to call setResult or
setErrorResult with an exception. In both cases Spring MVC dispatches the request back
to the Servlet container to complete processing. It is then treated either as if the
controller method returned the given value, or as if it produced the given exception.
The exception then goes through the regular exception handling mechanism, e.g. invoking
@ExceptionHandler methods.
When using Callable, similar processing logic follows. The main difference being that
the result is returned from the Callable or an exception is raised by it.
HandlerInterceptor's can also be AsyncHandlerInterceptor in order to receive the
afterConcurrentHandlingStarted callback on the initial request that starts asynchronous
processing instead of postHandle and afterCompletion.
HandlerInterceptor's can also register a CallableProcessingInterceptor
or a DeferredResultProcessingInterceptor in order to integrate more deeply with the
lifecycle of an asynchronous request for example to handle a timeout event. See
{api-spring-framework}/web/servlet/AsyncHandlerInterceptor.html[AsyncHandlerInterceptor]
for more details.
DeferredResult provides onTimeout(Runnable) and onCompletion(Runnable) callbacks.
See the Javadoc of DeferredResult for more details. Callable can be substituted for
WebAsyncTask that exposes additional methods for timeout and completion callbacks.
The Servlet API was originally built for making a single pass through the Filter-Servlet
chain. Asynchronous request processing, added in Servlet 3.0, allows applications to exit
the Filter-Servlet chain but leave the response open for further processing. The Spring MVC
async support is built around that mechanism. When a controller returns a DeferredResult,
the Filter-Servlet chain is exited and the Servlet container thread is released. Later when
the DeferredResult is set, an ASYNC dispatch (to the same URL) is made during which the
controller is mapped again but rather than invoking it, the DeferredResult value is used
(as if the controller returned it) to resume processing.
By contrast Spring WebFlux is neither built on the Servlet API, nor does it need such an asynchronous request processing feature because it is asynchronous by design. Asynchronous handling is built into all framework contracts and is intrinsically supported through :: stages of request processing.
From a programming model perspective, both Spring MVC and Spring WebFlux support asynchronous and Reactive types as return values in controller methods. Spring MVC even supports streaming, including reactive back pressure. However individual writes to the response remain blocking (and performed on a separate thread) unlike WebFlux that relies on non-blocking I/O and does not need an extra thread for each write.
Another fundamental difference is that Spring MVC does not support asynchronous or
reactive types in controller method arguments, e.g. @RequestBody, @RequestPart, and
others, nor does it have any explicit support for asynchronous and reactive types as
model attributes. Spring WebFlux does support all that.
DeferredResult and Callable can be used for a single asynchronous return value.
What if you want to produce multiple asynchronous values and have those written to the
response?
The ResponseBodyEmitter return value can be used to produce a stream of Objects, where
each Object sent is serialized with an
HttpMessageConverter and written to the
response. For example:
@GetMapping("/events")
public ResponseBodyEmitter handle() {
ResponseBodyEmitter emitter = new ResponseBodyEmitter();
// 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();ResponseBodyEmitter can also be used as the body in a ResponseEntity allowing you to
customize the status and headers of the response.
When an emitter throws an IOException (e.g. if the remote client went away) applications
are not responsible for cleaning up the connection, and should not invoke emitter.complete
or emitter.completeWithError. Instead the servlet container automatically initiates an
AsyncListener error notification in which Spring MVC makes a completeWithError call,
which in turn performs one a final ASYNC dispatch to the application during which Spring MVC
invokes the configured exception resolvers and completes the request.
SseEmitter is a sub-class of ResponseBodyEmitter that provides support for
Server-Sent Events where events sent from the server
are formatted according to the W3C SSE specification. In order to produce an SSE
stream from a controller simply return SseEmitter:
@GetMapping(path="/events", produces=MediaType.TEXT_EVENT_STREAM_VALUE)
public SseEmitter handle() {
SseEmitter emitter = new SseEmitter();
// 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();While SSE is the main option for streaming into browsers, note that Internet Explorer does not support Server-Sent Events. Consider using Spring’s WebSocket messaging with SockJS fallback transports (including SSE) that target a wide range of browsers.
Also see previous section for notes on exception handling.
Sometimes it is useful to bypass message conversion and stream directly to the response
OutputStream for example for a file download. Use the of the StreamingResponseBody
return value type to do that:
@GetMapping("/download")
public StreamingResponseBody handle() {
return new StreamingResponseBody() {
@Override
public void writeTo(OutputStream outputStream) throws IOException {
// write...
}
};
}StreamingResponseBody can be used as the body in a ResponseEntity allowing you to
customize the status and headers of the response.
Spring MVC supports use of reactive client libraries in a controller. This includes the
WebClient from spring-webflux and others such as Spring Data reactive data
repositories. In such scenarios it is convenient to be able to return reactive types
from the controller method .
Reactive return values are handled as follows:
-
A single-value promise is adapted to, and similar to using
DeferredResult. Examples includeMono(Reactor) orSingle(RxJava). -
A multi-value stream, with a streaming media type such as
"application/stream+json"or"text/event-stream", is adapted to, and similar to usingResponseBodyEmitterorSseEmitter. Examples includeFlux(Reactor) orObservable(RxJava). Applications can also returnFlux<ServerSentEvent>orObservable<ServerSentEvent>. -
A multi-value stream, with any other media type (e.g. "application/json"), is adapted to, and similar to using
DeferredResult<List<?>>.
|
Tip
|
Spring MVC supports Reactor and RxJava through the
{api-spring-framework}/core/ReactiveAdapterRegistry.html[ReactiveAdapterRegistry] from
|
When streaming to the response via reactive types, Spring MVC supports reactive back
pressure, but still needs to use blocking I/O to perform actual writes. This is done
through the configured MVC TaskExecutor on
a separate thread in order to avoid blocking the upstream source (e.g. a Flux returned
from the WebClient). By default a SyncTaskExecutor is used which is not suitable for
production. SPR-16203 will provide better
defaults in Spring Framework 5.1. In the mean time please configure the executor through
the MVC config.
The Servlet API does not provide any notification when a remote client goes away. Therefore while streaming to the response, whether via SseEmitter or <<mvc-ann-async-reactive-types,reactive types>, it is important to send data periodically, since the write would fail if the client has disconnected. The send could take the form of an empty (comment-only) SSE event, or any other data that the other side would have to to interpret as a heartbeat and ignore.
Alternatively consider using web messaging solutions such as STOMP over WebSocket or WebSocket with SockJS that have a built-in heartbeat mechanism.
The async request processing feature must be enabled at the Servlet container level. The MVC config also exposes several options for asynchronous requests.
Filter and Servlet declarations have an asyncSupported that needs to be set to true
in order enable asynchronous request processing. In addition, Filter mappings should be
declared to handle the ASYNC javax.servlet.DispatchType.
In Java configuration, when you use AbstractAnnotationConfigDispatcherServletInitializer
to initialize the Servlet container, this is done automatically.
In web.xml configuration, add <async-supported>true</async-supported> to the
DispatcherServlet and to Filter declarations, and also add
<dispatcher>ASYNC</dispatcher> to filter mappings.
The MVC config exposes options related to async request processing:
-
Java config — use the
configureAsyncSupportcallback onWebMvcConfigurer. -
XML namespace — use the
<async-support>element under<mvc:annotation-driven>.
You can configure the following:
-
Default timeout value for async requests, which if not set, depends on the underlying Servlet container (e.g. 10 seconds on Tomcat).
-
AsyncTaskExecutorto use for blocking writes when streaming with Reactive types, and also for executingCallable's returned from controller methods. It is highly recommended to configure this property if you’re streaming with reactive types or have controller methods that returnCallablesince by default it is aSimpleAsyncTaskExecutor. -
DeferredResultProcessingInterceptor's andCallableProcessingInterceptor's.
Note that the default timeout value can also be set on a DeferredResult,
ResponseBodyEmitter and SseEmitter. For a Callable, use WebAsyncTask to provide
a timeout value.
The Spring Security project provides support for protecting web applications from malicious exploits. Check out the Spring Security reference documentation including:
-
{doc-root}/spring-security/site/docs/current/reference/html5/#mvc[Spring MVC Security]
-
{doc-root}/spring-security/site/docs/current/reference/html5/#test-mockmvc[Spring MVC Test Support]
-
{doc-root}/spring-security/site/docs/current/reference/html5/#csrf[CSRF protection]
-
{doc-root}/spring-security/site/docs/current/reference/html5/#headers[Security Response Headers]
HDIV is another web security framework that integrates with Spring MVC.
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):
-
A
-1value won’t generate a'Cache-Control'response header. -
A
0value will prevent caching using the'Cache-Control: no-store'directive. -
An
n > 0value will cache the given response fornseconds using the'Cache-Control: max-age=n'directive.
The {api-spring-framework}/http/CacheControl.html[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 implements WebMvcConfigurer {
@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 HttpEntity, controllers can interact with the request/response using
HttpEntity types. Controllers returning ResponseEntity can include HTTP caching information
in responses like this:
@GetMapping("/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 appropriate response status and headers
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'or'If-Unmodified-Since'request header -
request.checkNotModified(eTag)compares eTag with the'If-None-Match'request header -
request.checkNotModified(eTag, lastModified)does both, meaning that both conditions should be valid
When receiving conditional 'GET'/'HEAD' requests, checkNotModified will check
that the resource has not been modified and if so, it will result in a HTTP 304 Not Modified
response. In case of conditional 'POST'/'PUT'/'DELETE' requests, checkNotModified
will check that the resource has not been modified and if it has been, it will result in a
HTTP 409 Precondition Failed response to prevent concurrent modifications.
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 by caching the content
written to the response and generating an MD5 hash over that to send as an ETag header.
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, lets the request be processed as usual, and
at the end compares the two hashes. If they are equal, a 304 is returned.
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 avoid computation.
This filter has a writeWeakETag parameter that configures the filter to write Weak ETags,
like this: W/"02a2d595e6ed9a0b24f027f2b63b134d6", as defined in
RFC 7232 Section 2.3.
The MVC Java config and the MVC XML namespace provide default configuration suitable for most applications along with a configuration API to customize it.
For more advanced customizations, not available in the configuration API, see Advanced Java Config and Advanced XML Config.
You do not need to understand the underlying beans created by the MVC Java config and the MVC namespace but if you want to learn more, see Special Bean Types and Web MVC Config.
In Java config use the @EnableWebMvc annotation:
@Configuration
@EnableWebMvc
public class WebConfig {
}In XML use the <mvc:annotation-driven> element:
<?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 number of Spring MVC infrastructure beans also adapting to dependencies available on the classpath: e.g. payload converters for JSON, XML, etc.
In Java config implement WebMvcConfigurer interface:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
// Implement configuration methods...
}In XML check attributes and sub-elements of <mvc:annotation-driven/>. 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.
In Java config, register custom formatters and converters:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addFormatters(FormatterRegistry registry) {
// ...
}
}In XML, the same:
<?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 FormatterRegistrar SPI
and the |
By default if Bean Validation is present
on the classpath — e.g. Hibernate Validator, the LocalValidatorFactoryBean is registered
as a global Validator for use with @Valid and Validated on
controller method arguments.
In Java config, you can customize the global Validator instance:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public Validator getValidator(); {
// ...
}
}In XML, the same:
<?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>Note that you can also register Validator's locally:
@Controller
public class MyController {
@InitBinder
protected void initBinder(WebDataBinder binder) {
binder.addValidators(new FooValidator());
}
}|
Tip
|
If you need to have a |
In Java config, register interceptors to apply to incoming requests:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new LocaleInterceptor());
registry.addInterceptor(new ThemeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**");
registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*");
}
}In XML, the same:
<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 request — e.g. Accept header, URL path extension, query parameter, etc.
By default the URL path extension is checked first — with json, xml, rss, and atom
registered as known extensions depending on classpath dependencies, and the "Accept" header
is checked second.
Consider changing those defaults to Accept header only and if you must use URL-based
content type resolution consider the query parameter strategy over the path extensions. See
Suffix match and Suffix match and RFD for
more details.
In Java config, customize requested content type resolution:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
configurer.mediaType("json", MediaType.APPLICATION_JSON);
}
}In XML, the same:
<mvc:annotation-driven content-negotiation-manager="contentNegotiationManager"/>
<bean id="contentNegotiationManager" class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
<property name="mediaTypes">
<value>
json=application/json
xml=application/xml
</value>
</property>
</bean>Customization of HttpMessageConverter can be achieved in Java config by overriding
{api-spring-framework}/web/servlet/config/annotation/WebMvcConfigurer.html#configureMessageConverters-java.util.List-[configureMessageConverters()]
if you want to replace the default converters created by Spring MVC, or by overriding
{api-spring-framework}/web/servlet/config/annotation/WebMvcConfigurer.html#extendMessageConverters-java.util.List-[extendMessageConverters()]
if you just want to customize them or add additional converters to the default ones.
Below is an example that adds Jackson JSON and XML converters with a customized
ObjectMapper instead of default ones:
@Configuration
@EnableWebMvc
public class WebConfiguration implements WebMvcConfigurer {
@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
Jackson2ObjectMapperBuilder builder = new Jackson2ObjectMapperBuilder()
.indentOutput(true)
.dateFormat(new SimpleDateFormat("yyyy-MM-dd"))
.modulesToInstall(new ParameterNamesModule());
converters.add(new MappingJackson2HttpMessageConverter(builder.build()));
converters.add(new MappingJackson2XmlHttpMessageConverter(builder.xml().build()));
}
}In this example,
{api-spring-framework}/http/converter/json/Jackson2ObjectMapperBuilder.html[Jackson2ObjectMapperBuilder]
is used to create a common configuration for both MappingJackson2HttpMessageConverter and
MappingJackson2XmlHttpMessageConverter with indentation enabled, a customized date format
and the registration of
jackson-module-parameter-names
that adds support for accessing parameter names (feature added in Java 8).
This builder customizes Jackson’s default properties with the following ones:
-
DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIESis disabled. -
MapperFeature.DEFAULT_VIEW_INCLUSIONis disabled.
It also automatically registers the following well-known modules if they are detected on the classpath:
-
jackson-datatype-jdk7: support for Java 7 types like
java.nio.file.Path. -
jackson-datatype-joda: support for Joda-Time types.
-
jackson-datatype-jsr310: support for Java 8 Date & Time API types.
-
jackson-datatype-jdk8: support for other Java 8 types like
Optional.
|
Note
|
Enabling indentation with Jackson XML support requires
|
Other interesting Jackson modules are available:
-
jackson-datatype-money: support for
javax.moneytypes (unofficial module) -
jackson-datatype-hibernate: support for Hibernate specific types and properties (including lazy-loading aspects)
It is also possible to do the same in XML:
<mvc:annotation-driven>
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper" ref="objectMapper"/>
</bean>
<bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter">
<property name="objectMapper" ref="xmlMapper"/>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
<bean id="objectMapper" class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean"
p:indentOutput="true"
p:simpleDateFormat="yyyy-MM-dd"
p:modulesToInstall="com.fasterxml.jackson.module.paramnames.ParameterNamesModule"/>
<bean id="xmlMapper" parent="objectMapper" p:createXmlMapper="true"/>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 implements WebMvcConfigurer {
@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 JSP and Jackson as a default View for JSON rendering:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@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, 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 implements WebMvcConfigurer {
@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 provides a convenient way to serve static resources from a list of {api-spring-framework}/core/io/Resource.html[Resource]-based locations.
In the example below, given a request that starts with "/resources", the relative path is
used to find and serve static resources relative to "/public" under the web application
root or on the classpath under "/static". The resources are served with a 1-year future
expiration to ensure maximum use of the browser cache and a reduction in HTTP requests
made by the browser. The Last-Modified header is also evaluated and if present a 304
status code is returned.
In Java config:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**")
.addResourceLocations("/public", "classpath:/static/")
.setCachePeriod(31556926);
}
}In XML:
<mvc:resources mapping="/resources/**"
location="/public, classpath:/static/"
cache-period="31556926" />The resource handler also supports a chain of {api-spring-framework}/web/servlet/resource/ResourceResolver.html[ResourceResolver]s and {api-spring-framework}/web/servlet/resource/ResourceTransformer.html[ResourceTransformer]s. which can be used to create a toolchain for working with optimized resources.
The VersionResourceResolver can be used for versioned resource URLs based on an MD5 hash
computed from the content, a fixed application version, or other. A
ContentVersionStrategy (MD5 hash) is a good choice with some notable exceptions such as
JavaScript resources used with a module loader.
For example in Java config;
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**")
.addResourceLocations("/public/")
.resourceChain(true)
.addResolver(new VersionResourceResolver().addContentVersionStrategy("/**"));
}
}In XML, the same:
<mvc:resources mapping="/resources/**" location="/public/">
<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>You can use ResourceUrlProvider to rewrite URLs and apply the full chain of resolvers and
transformers — e.g. to insert versions. The MVC config provides a ResourceUrlProvider
bean so it can be injected into others. You can also make the rewrite transparent with the
ResourceUrlEncodingFilter for Thymeleaf, JSPs, FreeMarker, and others with URL tags that
rely on HttpServletResponse#encodeURL.
WebJars is also supported via WebJarsResourceResolver
and automatically registered when "org.webjars:webjars-locator" is present on the
classpath. The resolver can re-write URLs to include the version of the jar and can also
match to incoming URLs without versions — e.g. "/jquery/jquery.min.js" to
"/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 implements WebMvcConfigurer {
@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 implements WebMvcConfigurer {
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable("myCustomDefaultServlet");
}
}Or in XML:
<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>This allows customizing options related to URL matching and treatment of the URL. For details on the individual options check out the {api-spring-framework}/web/servlet/config/annotation/PathMatchConfigurer.html[PathMatchConfigurer] API.
Example in Java config:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@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() {
//...
}
}In XML, the same:
<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"/>@EnableWebMvc imports DelegatingWebMvcConfiguration that (1) provides default Spring
configuration for Spring MVC applications and (2) detects and delegates to
WebMvcConfigurer's to customize that configuration.
For advanced mode, remove @EnableWebMvc and extend directly from
DelegatingWebMvcConfiguration instead of implementing WebMvcConfigurer:
@Configuration
public class WebConfig extends DelegatingWebMvcConfiguration {
// ...
}You can keep existing methods in WebConfig but you can now also override bean declarations
from the base class and you can still have any number of other WebMvcConfigurer's on
the classpath.
The MVC namespace does not have an advanced mode. If you need to customize a property on
a bean that you can’t change otherwise, you can use the BeanPostProcessor lifecycle
hook of the Spring ApplicationContext:
@Component
public class MyPostProcessor implements BeanPostProcessor {
public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {
// ...
}
}Note that MyPostProcessor needs to be declared as a bean either explicitly in XML or
detected through a <component scan/> declaration.
Servlet 4 containers are required to support HTTP/2 and Spring Framework 5 is compatible with Servlet API 4. From a programming model perspective there is nothing specific that applications need to do. However there are considerations related to server configuration. For more details please check out the HTTP/2 wiki page.
The Servlet API does expose one construct related to HTTP/2. The
javax.servlet.http.PushBuilder can used to proactively push resources to clients and it
is supported as a method argument to @RequestMapping methods.