webmvc.adoc

Spring Web MVC

Introduction

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.

DispatcherServlet

Same in Spring WebFlux

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 Container 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	In addition to using the ServletContext API directly, you can also extend AbstractAnnotationConfigDispatcherServletInitializer and override specific methods (see example under Context Hierarchy).

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. Filter and Servlet declarations are detected in Spring configuration and registered with the Servlet container. For more details check the Spring Boot docs.

Context Hierarchy

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 getRootConfigClasses() and null from getServletConfigClasses().

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 contextConfigLocation Servlet parameter empty.

Special Bean Types

Same in Spring WebFlux

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 one of the framework contracts listed in the table below. Spring MVC provides built-in implementations of these contracts but you can also customize, extend, or replace them.

Bean type	Explanation
HandlerMapping	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 HandlerMapping implementation. The two main HandlerMapping implementations are RequestMappingHandlerMapping which supports @RequestMapping annotated methods and SimpleUrlHandlerMapping which maintains explicit registrations of URI path patterns to handlers.
HandlerAdapter	Help the DispatcherServlet to invoke a handler mapped to a request regardless of how the handler is actually invoked. For example, invoking an annotated controller requires resolving annotations. The main purpose of a HandlerAdapter is to shield the DispatcherServlet from such details.
HandlerExceptionResolver	Strategy to resolve exceptions possibly mapping them to handlers, or to HTML error views, or other. See Exception Handling.
ViewResolver	Resolve logical String-based view names returned from a handler to an actual View to render to the response with. See View Resolution and [mvc-view].
LocaleResolver, LocaleContextResolver	Resolve the Locale a client is using and possibly their time zone, in order to be able to offer internationalized views. See Locale.
ThemeResolver	Resolve themes your web application can use, for example, to offer personalized layouts. See Themes.
MultipartResolver	Abstraction for parsing a multi-part request (e.g. browser form file upload) with the help of some multipart parsing library. See Multipart requests.
FlashMapManager	Store and retrieve the "input" and the "output" FlashMap that can be used to pass attributes from one request to another, usually across a redirect. See Flash attributes.

Framework Config

Same in Spring WebFlux

For each type of special bean, the DispatcherServlet checks for the WebApplicationContext first. If there are no matching bean types, it falls back on the default types listed in DispatcherServlet.properties.

Applications can declare the special beans they wish to have. Most applications however will find a better starting point in the MVC Java config or the MVC XML namespace which provide a higher level configuration API that in turn make the necessary bean declarations. See MVC Config for more details.

Note	Spring Boot relies on the MVC Java config to configure Spring MVC and also provides many extra convenient options on top.

Container Config

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.

Processing

Same in Spring WebFlux

The DispatcherServlet processes requests as follows:

• The WebApplicationContext is searched for and bound in the request as an attribute that the controller and other elements in the process can use. It is bound by default under the key DispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTE.

• 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 MultipartHttpServletRequest for further processing by other elements in the process. See Multipart requests 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 Exception Handling 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.

Table 1. DispatcherServlet initialization parameters

Parameter	Explanation
contextClass	Class that implements WebApplicationContext, which instantiates the context used by this Servlet. By default, the XmlWebApplicationContext is used.
contextConfigLocation	String that is passed to the context instance (specified by contextClass) to indicate where context(s) can be found. The string consists potentially of multiple strings (using a comma as a delimiter) to support multiple contexts. In case of multiple context locations with beans that are defined twice, the latest location takes precedence.
namespace	Namespace of the WebApplicationContext. Defaults to [servlet-name]-servlet.

Interception

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 a 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.

View Resolution

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.

This table below provides more details on the ViewResolver hierarchy:

Table 2. ViewResolver implementations

ViewResolver	Description
AbstractCachingViewResolver	Sub-classes of AbstractCachingViewResolver cache view instances that they resolve. Caching improves performance of certain view technologies. It’s possible to turn off the cache by setting the cache property to false. Furthermore, if you must refresh a certain view at runtime (for example when a FreeMarker template is modified), you can use the removeFromCache(String viewName, Locale loc) method.
XmlViewResolver	Implementation of ViewResolver that accepts a configuration file written in XML with the same DTD as Spring’s XML bean factories. The default configuration file is /WEB-INF/views.xml.
ResourceBundleViewResolver	Implementation of ViewResolver that uses bean definitions in a ResourceBundle, specified by the bundle base name, and for each view it is supposed to resolve, it uses the value of the property [viewname].(class) as the view class and the value of the property [viewname].url as the view url. Examples can be found in the chapter on [mvc-view].
UrlBasedViewResolver	Simple implementation of the ViewResolver interface that effects the direct resolution of logical view names to URLs, without an explicit mapping definition. This is appropriate if your logical names match the names of your view resources in a straightforward manner, without the need for arbitrary mappings.
InternalResourceViewResolver	Convenient subclass of UrlBasedViewResolver that supports InternalResourceView (in effect, Servlets and JSPs) and subclasses such as JstlView and TilesView. You can specify the view class for all views generated by this resolver by using setViewClass(..). See the UrlBasedViewResolver javadocs for details.
FreeMarkerViewResolver	Convenient subclass of UrlBasedViewResolver that supports FreeMarkerView and custom subclasses of them.
ContentNegotiatingViewResolver	Implementation of the ViewResolver interface that resolves a view based on the request file name or Accept header. See Content negotiation.

You chain view resolvers by configuring more than one resolver 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 view resolver specifies that a view resolver 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. There an InternalResourceViewResolver must always be configured last in the order.

See View Controllers under MVC Config for details on how to configure view resolution. Also see[mvc-view] for more details on supported view technologies.

Redirect

The special redirect: prefix in a view name allows you to perform a redirect. The UrlBasedViewResolver (and subclasses) will recognize this as a special indication that a redirect is needed. The rest of the view name will be treated as the redirect URL.

The net effect is the same as if the controller had returned a RedirectView, but now the controller itself can simply operate in terms of logical view names. A logical view name such as redirect:/myapp/some/resource will redirect relative to the current Servlet context, while a name such as redirect:http://myhost.com/some/arbitrary/path will redirect to an absolute URL.

Note that if a controller method is annotated with the @ResponseStatus, the annotation value takes precedence over the response status set by RedirectView.

Forward

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.

Content negotiation

{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.

Locale

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.

TimeZone

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.

Header resolver

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.

Cookie resolver

This locale resolver inspects a Cookie that might exist on the client to see if a Locale or TimeZone is specified. If so, it uses the specified details. Using the properties of this locale resolver, you can specify the name of the cookie as well as the maximum age. Find below an example of defining a CookieLocaleResolver.

<bean id="localeResolver" class="org.springframework.web.servlet.i18n.CookieLocaleResolver">

	<property name="cookieName" value="clientlanguage"/>

	<!-- in seconds. If set to -1, the cookie is not persisted (deleted when browser shuts down) -->
	<property name="cookieMaxAge" value="100000"/>

</bean>

Table 3. CookieLocaleResolver properties

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.

Session resolver

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.

Locale interceptor

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>

Themes

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.

Define a theme

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.

Resolve themes

After you define themes, as in the preceding section, you decide which theme to use. The DispatcherServlet will look for a bean named themeResolver to find out which ThemeResolver implementation to use. A theme resolver works in much the same way as a LocaleResolver. It detects the theme to use for a particular request and can also alter the request’s theme. The following theme resolvers are provided by Spring:

Table 4. ThemeResolver implementations

Class	Description
FixedThemeResolver	Selects a fixed theme, set using the defaultThemeName property.
SessionThemeResolver	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.
CookieThemeResolver	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.

Multipart requests

Spring has built-in support for multipart requests including file uploads. You enable this multipart support with pluggable MultipartResolver objects, defined in the org.springframework.web.multipart package. Spring provides one MultipartResolver implementation for use with Commons FileUpload and another for use with Servlet 3.0 multipart request parsing.

By default, Spring does no multipart handling, because some developers want to handle multiparts themselves. You enable Spring multipart handling by adding a multipart resolver to the web application’s context. Each request is inspected to see if it contains a multipart. If no multipart is found, the request continues as expected. If a multipart is found in the request, the MultipartResolver that has been declared in your context is used. After that, the multipart attribute in your request is treated like any other attribute.

Commons FileUpload

To use Apache Commons FileUpload, 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.

When the Spring DispatcherServlet detects a multipart request, it activates the resolver that has been declared in your context and hands over the request. The resolver then wraps the current HttpServletRequest into a MultipartHttpServletRequest that supports multipart file uploads. Using the MultipartHttpServletRequest, you can get information about the multiparts contained by this request and actually get access to the multipart files themselves in your controllers.

Servlet 3.0

In order to use Servlet 3.0 based multipart parsing, you need to mark the DispatcherServlet with a "multipart-config" section in web.xml, or with a javax.servlet.MultipartConfigElement in programmatic Servlet registration, or in case of a custom Servlet class possibly with a javax.servlet.annotation.MultipartConfig annotation on your Servlet class. Configuration settings such as maximum sizes or storage locations need to be applied at that Servlet registration level as Servlet 3.0 does not allow for those settings to be done from the MultipartResolver.

Once Servlet 3.0 multipart parsing has been enabled in one of the above mentioned ways you can add a bean of type StandardServletMultipartResolver and with the name multipartResolver to your Spring configuration.

Filters

The spring-web module provides some useful filters.

HTTP PUT Form

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.

Forwarded Headers

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.

Shallow ETag

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.

CORS

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 CorsFilter for more details.

Annotated Controllers

Same in Spring WebFlux

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.

Declaration

Same in Spring WebFlux

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 annotated with @Controller and @ResponseBody indicating a controller whose every method inherits the type-level @ResponseBody annotation and therefore writes to the response body (vs model-and-vew rendering).

AOP proxies

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"/>.

Request Mapping

Same in Spring WebFlux

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 shortcut variants are composed annotations — themselves annotated with @RequestMapping. They are commonly used at the method level. At the class level an @RequestMapping is more useful for expressing shared mappings.

@RestController
@RequestMapping("/persons")
class PersonController {

	@GetMapping("/{id}")
	public Person getPerson(@PathVariable Long id) {
		// ...
	}

	@PostMapping
	@ResponseStatus(HttpStatus.CREATED)
	public void add(@RequestBody Person person) {
		// ...
	}
}

URI patterns

Same in Spring WebFlux

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 [mvc-ann-webdatabinder].

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 PathMatcher contract and the AntPathMatcher implementation from spring-core for URI path matching.

Pattern comparison

Same in Spring WebFlux

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.

Suffix match

By default Spring MVC performs ".*" suffix pattern matching so that a controller mapped to /person is also implicitly mapped to /person.*. This is used for URL based content negotiation, e.g. /person.pdf, /person.xml, etc.

Suffix pattern matching was quite helpful when browsers used to send Accept headers that are hard to interpet consistently. In the present, and for REST services, the Accept header should be the preferred choice.

Suffix patterns can cause ambiguity and complexity in combination with path parameters, encoded characters, and URI variables. It also makes it harder to reason about URL-based authorization rules and security (see Suffix match and RFD).

Suffix pattern matching can be turned off completely or restricted to a set of explicitly registered path extensions. We strongly recommend using of one those options. See Path Matching and Content Types. If you need URL based content negotiation consider using query parameters instead.

Suffix match and RFD

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.

Matrix variables

The URI specification RFC 3986 defines the possibility of including name-value pairs within path segments. There is no specific term used in the spec. The general "URI path parameters" could be applied although the more unique "Matrix URIs", originating from an old post by Tim Berners-Lee, is also frequently used and fairly well known. Within Spring MVC these are referred to as matrix variables.

Matrix variables can appear in any path segment, each matrix variable separated with a ";" (semicolon). For example: "/cars;color=red;year=2012". Multiple values may be either "," (comma) separated "color=red,green,blue" or the variable name may be repeated "color=red;color=green;color=blue".

If a URL is expected to contain matrix variables, the request mapping pattern must represent them with a URI template. This ensures the request can be matched correctly regardless of whether matrix variables are present or not and in what order they are provided.

Below is an example of extracting the matrix variable "q":

// GET /pets/42;q=11;r=22

@GetMapping("/pets/{petId}")
public void findPet(@PathVariable String petId, @MatrixVariable int q) {

	// petId == 42
	// q == 11
}

Since all path segments may contain matrix variables, in some cases you need to be more specific to identify where the variable is expected to be:

// GET /owners/42;q=11/pets/21;q=22

@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
}

All matrix variables may be obtained in a Map:

// 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 to enable the use of matrix variables, you must set the removeSemicolonContent property of RequestMappingHandlerMapping to false. By default it is set to true.

Tip

The MVC Java config and the MVC namespace both provide options for enabling the use of matrix variables. If you are using Java config, The Advanced Customizations with MVC Java Config section describes how the RequestMappingHandlerMapping can be customized. In the MVC namespace, the <mvc:annotation-driven> element has an enable-matrix-variables attribute that should be set to true. By default it is set to false. <?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation=" http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd"> <mvc:annotation-driven enable-matrix-variables="true"/> </beans>

Consumable media types

Same in Spring WebFlux

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	MediaType provides constants for commonly used media types — e.g. APPLICATION_JSON_VALUE, APPLICATION_JSON_UTF8_VALUE.

Producible media types

Same in Spring WebFlux

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	MediaType provides constants for commonly used media types — e.g. APPLICATION_JSON_VALUE, APPLICATION_JSON_UTF8_VALUE.

Parameters, headers

Same in Spring WebFlux

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) {
	// ...
}

Tip	You can match Content-Type and Accept with the headers condition but it is better to use consumes and produces instead.

HTTP HEAD, OPTIONS

Same in Spring WebFlux

@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.

Handler Methods

Same in Spring WebFlux

@RequestMapping handler methods have a flexible signature and can choose from a range of supported controller method arguments and return values.

Method Arguments

Same in Spring WebFlux

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
WebRequest, NativeWebRequest	Generic access to request parameters, request & session attributes, without direct use of the Servlet API.
javax.servlet.ServletRequest, javax.servlet.ServletResponse	Choose any specific request or response type — e.g. ServletRequest, HttpServletRequest, or Spring’s MultipartRequest, MultipartHttpServletRequest.
javax.servlet.http.HttpSession	Enforces the presence of a session. As a consequence, such an argument is never null. Note: Session access is not thread-safe. Consider setting the RequestMappingHandlerAdapter's "synchronizeOnSession" flag to "true" if multiple requests are allowed to access a session concurrently.
javax.servlet.http.PushBuilder	Servlet 4.0 push builder API for programmatic HTTP/2 resource pushes. Note that per Servlet spec, the injected PushBuilder instance can be null if the client does not support that HTTP/2 feature.
java.security.Principal	Currently authenticated user; possibly a specific Principal implementation class if known.
HttpMethod	The HTTP method of the request.
java.util.Locale	The current request locale, determined by the most specific LocaleResolver available, in effect, the configured LocaleResolver/LocaleContextResolver.
Java 6+: java.util.TimeZone Java 8+: java.time.ZoneId	The time zone associated with the current request, as determined by a LocaleContextResolver.
java.io.InputStream, java.io.Reader	For access to the raw request body as exposed by the Servlet API.
java.io.OutputStream, java.io.Writer	For access to the raw response body as exposed by the Servlet API.
@PathVariable	For access to URI template variables. See URI patterns.
@MatrixVariable	For access to name-value pairs in URI path segments. See Matrix variables.
@RequestParam	For access to Servlet request parameters. Parameter values are converted to the declared method argument type. See @RequestParam.
@RequestHeader	For access to request headers. Header values are converted to the declared method argument type. See @RequestHeader.
@RequestBody	For access to the HTTP request body. Body content is converted to the declared method argument type using HttpMessageConverters. See @RequestBody.
HttpEntity<B>	For access to request headers and body. The body is converted with HttpMessageConverters. See HttpEntity.
@RequestPart	For access to a part in a "multipart/form-data" request. See @RequestPart and Multipart requests.
java.util.Map, org.springframework.ui.Model, org.springframework.ui.ModelMap	For access and updates of the implicit model that is exposed to the web view.
RedirectAttributes	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.
Command or form object (with optional @ModelAttribute)	Command object whose properties to bind to request parameters — via setters or directly to fields, with customizable type conversion, depending on @InitBinder methods and/or the HandlerAdapter configuration (see the webBindingInitializer property on RequestMappingHandlerAdapter). Command objects along with their validation results are exposed as model attributes, by default using the command class name - e.g. model attribute "orderAddress" for a command object of type "some.package.OrderAddress". @ModelAttribute can be used to customize the model attribute name.
Errors, BindingResult	Validation results for the command/form object data binding; this argument must be declared immediately after the command/form object in the controller method signature.
SessionStatus	For marking form processing complete which triggers cleanup of session attributes declared through a class-level @SessionAttributes annotation.
UriComponentsBuilder	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 Forwarded and X-Forwarded-* headers.
@SessionAttribute	For access to any session attribute; in contrast to model attributes stored in the session as a result of a class-level @SessionAttributes declaration.
@RequestAttribute	For access to request attributes.

Return Values

Same in Spring WebFlux

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
@ResponseBody	The return value is converted through HttpMessageConverters and written to the response. See @ResponseBody.
HttpEntity<B>, ResponseEntity<B>	The return value specifies the full response including HTTP headers and body be converted through HttpMessageConverters and written to the response. See HttpEntity.
HttpHeaders	For returning a response with headers and no body.
String	A view name to be resolved with ViewResolver's and used together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method may also programmatically enrich the model by declaring a Model argument (see above).
View	A View instance to use for rendering together with the implicit model — determined through command objects and @ModelAttribute methods. The handler method may also programmatically enrich the model by declaring a Model argument (see above).
java.util.Map, org.springframework.ui.Model	Attributes to be added to the implicit model with the view name implicitly determined through a RequestToViewNameTranslator.
ModelAndView object	The view and model attributes to use, and optionally a response status.
void	A method with a void return type (or null return value) is considered to have fully handled the response if it also has a ServletResponse, or an OutputStream argument, or an @ResponseStatus annotation. The same is true also if the controller has made a positive ETag or lastModified timestamp check (see @Controller caching for details). If none of the above is true, a void return type may also indicate "no response body" for REST controllers, or default view name selection for HTML controllers.
Callable<V>	Produce any of the above return values asynchronously in a Spring MVC managed thread.
DeferredResult<V>	Produce any of the above return values asynchronously from any thread — e.g. possibly as a result of some event or callback.
ListenableFuture<V>, java.util.concurrent.CompletionStage<V>, java.util.concurrent.CompletableFuture<V>	Alternative to DeferredResult as a convenience for example when an underlying service returns one of those.
ResponseBodyEmitter, SseEmitter	Emit a stream of objects asynchronously to be written to the response with HttpMessageConverter's; also supported as the body of a ResponseEntity.
StreamingResponseBody	Write to the response OutputStream asynchronously; also supported as the body of a ResponseEntity.
Reactive types — Reactor, RxJava, or others via ReactiveAdapterRegistry	Alternative to `DeferredResult with multi-value streams (e.g. Flux, Observable) collected to a List. For streaming scenarios — .e.g. text/event-stream, application/json+stream, SseEmitter and ResponseBodyEmitter are used instead, where ServletOutputStream blocking I/O is performed on a Spring MVC managed thread and back pressure applied against the completion of each write. See Reactive return values.
Any other return type	A single model attribute to be added to the implicit model with the view name implicitly determined through a RequestToViewNameTranslator; the attribute name may be specified through a method-level @ModelAttribute or otherwise a name is selected based on the class name of the return type.

@RequestParam

Use the @RequestParam annotation to bind request parameters to a method parameter in your controller.

The following code snippet shows the usage:

@Controller
@RequestMapping("/pets")
@SessionAttributes("pet")
public class EditPetForm {

	// ...

	@GetMapping
	public String setupForm(@RequestParam("petId") int petId, ModelMap model) {
		Pet pet = this.clinic.loadPet(petId);
		model.addAttribute("pet", pet);
		return "petForm";
	}

	// ...

}

Parameters using this annotation are required by default, but you can specify that a parameter is optional by setting @RequestParam's required attribute to false (e.g., @RequestParam(name="id", required=false)).

Type conversion is applied automatically if the target method parameter type is not String. See Type Conversion.

When an @RequestParam annotation is used on a Map<String, String> or MultiValueMap<String, String> argument, the map is populated with all request parameters.

Type Conversion

String-based values extracted from the request including request parameters, path variables, request headers, and cookie values may need to be converted to the target type of the method parameter or field (e.g., binding a request parameter to a field in an @ModelAttribute parameter) they’re bound to. If the target type is not String, Spring automatically converts to the appropriate type. All simple types such as int, long, Date, etc. are supported. You can further customize the conversion process through a WebDataBinder, see Binder Methods, or by registering Formatters with the FormattingConversionService, see Spring Field Formatting.

@RequestHeader

The @RequestHeader annotation allows a method parameter to be bound to a request header.

Here is a sample request header:

Host                    localhost:8080
Accept                  text/html,application/xhtml+xml,application/xml;q=0.9
Accept-Language         fr,en-gb;q=0.7,en;q=0.3
Accept-Encoding         gzip,deflate
Accept-Charset          ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive              300

The following code sample demonstrates how to get the value of the Accept-Encoding and Keep-Alive headers:

@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@RequestHeader("Accept-Encoding") String encoding,
		@RequestHeader("Keep-Alive") long keepAlive) {
	//...
}

Type conversion is applied automatically if the method parameter is not String. See 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 @RequestHeader("Accept") may be of type String but also String[] or List<String>.

@CookieValue

The @CookieValue annotation allows a method parameter to be bound to the value of an HTTP cookie.

Let us consider that the following cookie has been received with an http request:

JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84

The following code sample demonstrates how to get the value of the JSESSIONID cookie:

@RequestMapping("/displayHeaderInfo.do")
public void displayHeaderInfo(@CookieValue("JSESSIONID") String cookie) {
	//...
}

Type conversion is applied automatically if the target method parameter type is not String. See Type Conversion.

@ModelAttribute

As explained in the previous section @ModelAttribute can be used on methods or on method arguments. This section explains its usage on method arguments.

An @ModelAttribute on a method argument indicates the argument should be retrieved from the model. If not present in the model, the argument should be instantiated first and then added to the model. Once present in the model, the argument’s fields should be populated from all request parameters that have matching names. This is known as data binding in Spring MVC, a very useful mechanism that saves you from having to parse each form field individually.

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute Pet pet) { }

Given the above example where can the Pet instance come from? There are several options:

• It may already be in the model due to use of @SessionAttributes — see [mvc-ann-sessionattrib].

• It may already be in the model due to an @ModelAttribute method in the same controller — as explained in the previous section.

• It may be retrieved based on a URI template variable and type converter (explained in more detail below).

• It may be instantiated using its default constructor.

An @ModelAttribute method is a common way to retrieve an attribute from the database, which may optionally be stored between requests through the use of @SessionAttributes. In some cases it may be convenient to retrieve the attribute by using an URI template variable and a type converter. Here is an example:

@PutMapping("/accounts/{account}")
public String save(@ModelAttribute("account") Account account) {
	// ...
}

In this example the name of the model attribute (i.e. "account") matches the name of a URI template variable. If you register Converter<String, Account> that can turn the String account value into an Account instance, then the above example will work without the need for an @ModelAttribute method.

The next step is data binding. The WebDataBinder class matches request parameter names — including query string parameters and form fields — to model attribute fields by name. Matching fields are populated after type conversion (from String to the target field type) has been applied where necessary. Data binding and validation are covered in Validation. Customizing the data binding process for a controller level is covered in [mvc-ann-webdatabinder].

As a result of data binding there may be errors such as missing required fields or type conversion errors. To check for such errors add a BindingResult argument immediately following the @ModelAttribute argument:

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

With a BindingResult you can check if errors were found in which case it’s common to render the same form where the errors can be shown with the help of Spring’s <errors> form tag.

Note that in some cases it may be useful to gain access to an attribute in the model without data binding. For such cases you may inject the Model into the controller or alternatively use the binding flag on the annotation:

@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) {
		// ...
	}

In addition to data binding you can also invoke validation using your own custom validator passing the same BindingResult that was used to record data binding errors. That allows for data binding and validation errors to be accumulated in one place and subsequently reported back to the user:

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) {
	new PetValidator().validate(pet, result);
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

Or you can have validation invoked automatically by adding the JSR-303 @Valid annotation:

@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) {
	if (result.hasErrors()) {
		return "petForm";
	}
	// ...
}

See Bean validation and Spring validation for details on how to configure and use validation.

File upload

After the MultipartResolver completes its job, the request is processed like any other. First, create a form with a file input that will allow the user to upload a form. The encoding attribute ( enctype="multipart/form-data") lets the browser know how to encode the form as multipart request:

<html>
	<head>
		<title>Upload a file please</title>
	</head>
	<body>
		<h1>Please upload a file</h1>
		<form method="post" action="/form" enctype="multipart/form-data">
			<input type="text" name="name"/>
			<input type="file" name="file"/>
			<input type="submit"/>
		</form>
	</body>
</html>

The next step is to create a controller that handles the file upload. This controller is very similar to a normal annotated @Controller, except that we use MultipartHttpServletRequest or MultipartFile in the method parameters:

@Controller
public class FileUploadController {

	@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 how the @RequestParam method parameters map to the input elements declared in the form. In this example, nothing is done with the byte[], but in practice you can save it in a database, store it on the file system, and so on.

When using Servlet 3.0 multipart parsing you can also use javax.servlet.http.Part for the method parameter:

@Controller
public class FileUploadController {

	@PostMapping("/form")
	public String handleFormUpload(@RequestParam("name") String name,
			@RequestParam("file") Part file) {

		InputStream inputStream = file.getInputStream();
		// store bytes from uploaded file somewhere

		return "redirect:uploadSuccess";
	}

}

@SessionAttributes

@SessionAttributes is used to store model attributes in the HTTP session between requests. It is a type-level annotation that declares session attributes used by a specific handler. This will typically list the names of model attributes or types of model attributes which should be transparently stored in the session or some conversational storage, serving as form-backing beans between subsequent requests.

The following code snippet shows the usage of this annotation, specifying the model attribute name:

@Controller
@RequestMapping("/editPet.do")
@SessionAttributes("pet")
public class EditPetForm {
	// ...
}

@SessionAttribute

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 [mvc-ann-sessionattrib].

@RequestAttribute

Similar to @SessionAttribute the @RequestAttribute annotation can be used to access pre-existing request attributes created by a filter or interceptor:

@RequestMapping("/")
public String handle(@RequestAttribute Client client) {
	// ...
}

Redirect attributes

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

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.

Matching requests to flash attributes

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 .

@RequestPart

Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. All of the above examples and configuration apply here as well. However, unlike browsers that typically submit files and simple form fields, a programmatic client can also send more complex data of a specific content type — for example a multipart request with a file and second part with JSON formatted data:

POST /someUrl
Content-Type: multipart/mixed

--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="meta-data"
Content-Type: application/json; charset=UTF-8
Content-Transfer-Encoding: 8bit

{
	"name": "value"
}
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="file-data"; filename="file.properties"
Content-Type: text/xml
Content-Transfer-Encoding: 8bit
... File Data ...

You could access the part named "meta-data" with a @RequestParam("meta-data") String metadata controller method argument. However, you would probably prefer to accept a strongly typed object initialized from the JSON formatted data in the body of the request part, very similar to the way @RequestBody converts the body of a non-multipart request to a target object with the help of an HttpMessageConverter.

You can use the @RequestPart annotation instead of the @RequestParam annotation for this purpose. It allows you to have the content of a specific multipart passed through an HttpMessageConverter taking into consideration the 'Content-Type' header of the multipart:

@PostMapping("/someUrl")
public String onSubmit(@RequestPart("meta-data") MetaData metadata,
		@RequestPart("file-data") MultipartFile file) {

	// ...

}

Notice how MultipartFile method arguments can be accessed with @RequestParam or with @RequestPart interchangeably. However, the @RequestPart("meta-data") MetaData method argument in this case is read as JSON content based on its 'Content-Type' header and converted with the help of the MappingJackson2HttpMessageConverter.

@RequestBody

The @RequestBody method parameter annotation indicates that a method parameter should be bound to the value of the HTTP request body. For example:

@PutMapping("/something")
public void handle(@RequestBody String body, Writer writer) throws IOException {
	writer.write(body);
}

You convert the request body to the method argument by using an HttpMessageConverter. HttpMessageConverter is responsible for converting from the HTTP request message to an object and converting from an object to the HTTP response body. The RequestMappingHandlerAdapter supports the @RequestBody annotation with the following default HttpMessageConverters:

• ByteArrayHttpMessageConverter converts byte arrays

• StringHttpMessageConverter converts strings

• FormHttpMessageConverter converts form data to/from a MultiValueMap<String, String>

• SourceHttpMessageConverter converts to/from a javax.xml.transform.Source`

For more information on these converters, see Message Converters. Also note that if using the MVC namespace or the MVC Java config, a wider range of message converters are registered by default, including default JSON and XML payload converters (if e.g. Jackson, Gson and/or JAXB2 are present at runtime). See Enable MVC Config for more information on MVC setup options.

For a custom example, if you intend to read and write XML using the spring-oxm module, you need to configure the MarshallingHttpMessageConverter with a specific Marshaller implementation from the org.springframework.oxm package. The example below shows how to do that directly in your configuration but if your application is configured through the MVC namespace or the MVC Java config see Enable MVC Config instead.

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
	<property name="messageConverters">
		<list>
			<ref bean="stringHttpMessageConverter"/>
			<ref bean="marshallingHttpMessageConverter"/>
		<list>
	</property>
</bean>

<bean id="stringHttpMessageConverter"
		class="org.springframework.http.converter.StringHttpMessageConverter"/>

<bean id="marshallingHttpMessageConverter"
		class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
	<constructor-arg ref="xstreamMarshaller"/>
</bean>

<bean id="xstreamMarshaller" class="org.springframework.oxm.xstream.XStreamMarshaller"/>

An @RequestBody method parameter can be annotated with @Valid, in which case it will be validated using the configured Validator instance. When using the MVC namespace or the MVC Java config, a JSR-303 validator is configured automatically assuming a JSR-303 implementation is available on the classpath.

Just like with @ModelAttribute parameters, an Errors argument can be used to examine the errors. If such an argument is not declared, a MethodArgumentNotValidException will be raised. The exception is handled in the DefaultHandlerExceptionResolver, which sends a 400 error back to the client.

Note	Also see Enable MVC Config for information on configuring message converters and a validator through the MVC namespace or the MVC Java config.

HttpEntity

HttpEntity is similar to @RequestBody but also with access to request headers:

@RequestMapping("/something")
public ResponseEntity<String> handle(HttpEntity<byte[]> requestEntity) throws UnsupportedEncodingException {
	String requestHeader = requestEntity.getHeaders().getFirst("MyRequestHeader");
	byte[] requestBody = requestEntity.getBody();
	// ...
}

The above example gets the value of the MyRequestHeader request header, and reads the body as a byte array. As with @RequestBody, Spring uses HttpMessageConverter to convert from and to the request and response streams. For more information on these converters, see the previous section and Message Converters.

@ResponseBody

The @ResponseBody annotation is similar to @RequestBody. This annotation can be placed on a method and indicates that the return type should be written straight to the HTTP response body (and not placed in a Model, or interpreted as a view name). For example:

@GetMapping("/something")
@ResponseBody
public String helloWorld() {
	return "Hello World";
}

The above example will result in the text Hello World being written to the HTTP response stream.

As with @RequestBody, Spring converts the returned object to a response body by using an HttpMessageConverter. For more information on these converters, see the previous section and Message Converters.

ResponseEntity

The is similar to @ResponseBody but besides providing the response body, ResponseEntity also allows setting response headers:

@PostMapping("/something")
public ResponseEntity<String> handle() {
	// ...
	URI location = ... ;
	return new ResponseEntity.created(location).build();
}

As with @ResponseBody, Spring uses HttpMessageConverter to convert from and to the request and response streams. For more information on these converters, see the previous section and Message Converters.

Jackson JSON

Jackson serialization views

It can sometimes be useful to filter contextually the object that will be serialized to the HTTP response body. In order to provide such capability, Spring MVC has built-in support for rendering with Jackson’s Serialization Views.

To use it with an @ResponseBody controller method or controller methods that return ResponseEntity, simply add the @JsonView annotation with a class argument specifying the view class or interface to be used:

@RestController
public class UserController {

	@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	Note that despite @JsonView allowing for more than one class to be specified, the use on a controller method is only supported with exactly one class argument. Consider the use of a composite interface if you need to enable multiple views.

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";
	}
}

Jackson JSONP

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.

Model Methods

The @ModelAttribute annotation can be used on methods or on method arguments. This section explains its usage on methods while the next section explains its usage on method arguments.

An @ModelAttribute on a method indicates the purpose of that method is to add one or more model attributes. Such methods support the same argument types as @RequestMapping methods but cannot be mapped directly to requests. Instead @ModelAttribute methods in a controller are invoked before @RequestMapping methods, within the same controller. A couple of examples:

// Add one attribute
// The return value of the method is added to the model under the name "account"
// You can customize the name via @ModelAttribute("myAccount")

@ModelAttribute
public Account addAccount(@RequestParam String number) {
	return accountManager.findAccount(number);
}

// Add multiple attributes

@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
	model.addAttribute(accountManager.findAccount(number));
	// add more ...
}

@ModelAttribute methods are used to populate the model with commonly needed attributes for example to fill a drop-down with states or with pet types, or to retrieve a command object like Account in order to use it to represent the data on an HTML form. The latter case is further discussed in the next section.

Note the two styles of @ModelAttribute methods. In the first, the method adds an attribute implicitly by returning it. In the second, the method accepts a Model and adds any number of model attributes to it. You can choose between the two styles depending on your needs.

A controller can have any number of @ModelAttribute methods. All such methods are invoked before @RequestMapping methods of the same controller.

@ModelAttribute methods can also be defined in an @ControllerAdvice-annotated class and such methods apply to many controllers. See the Controller Advice section for more details.

Tip

What happens when a model attribute name is not explicitly specified? In such cases a default name is assigned to the model attribute based on its type. For example if the method returns an object of type Account, the default name used is "account". You can change that through the value of the @ModelAttribute annotation. If adding attributes directly to the Model, use the appropriate overloaded addAttribute(..) method - i.e., with or without an attribute name.

The @ModelAttribute annotation can be used on @RequestMapping methods as well. In that case the return value of the @RequestMapping method is interpreted as a model attribute rather than as a view name. The view name is then derived based on view name conventions instead, much like for methods returning void — see Default view name.

Binder Methods

To customize request parameter binding with PropertyEditors through Spring’s WebDataBinder, you can use @InitBinder-annotated methods within your controller, @InitBinder methods within an @ControllerAdvice class, or provide a custom WebBindingInitializer. See the Controller Advice section for more details.

Annotating controller methods with @InitBinder allows you to configure web data binding directly within your controller class. @InitBinder identifies methods that initialize the WebDataBinder that will be used to populate command and form object arguments of annotated handler methods.

Such init-binder methods support all arguments that @RequestMapping methods support, except for command/form objects and corresponding validation result objects. Init-binder methods must not have a return value. Thus, they are usually declared as void. Typical arguments include WebDataBinder in combination with WebRequest or java.util.Locale, allowing code to register context-specific editors.

The following example demonstrates the use of @InitBinder to configure a CustomDateEditor for all java.util.Date form properties.

@Controller
public class MyFormController {

	@InitBinder
	protected void initBinder(WebDataBinder binder) {
		SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
		dateFormat.setLenient(false);
		binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
	}

	// ...
}

Alternatively, as of Spring 4.2, consider using addCustomFormatter to specify Formatter implementations instead of PropertyEditor instances. This is particularly useful if you happen to have a Formatter-based setup in a shared FormattingConversionService as well, with the same approach to be reused for controller-specific tweaking of the binding rules.

@Controller
public class MyFormController {

	@InitBinder
	protected void initBinder(WebDataBinder binder) {
		binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd"));
	}

	// ...
}

Controller Advice

The @ControllerAdvice annotation is a component annotation allowing implementation classes to be auto-detected through classpath scanning. It is automatically enabled when using the MVC namespace or the MVC Java config.

Classes annotated with @ControllerAdvice can contain @ExceptionHandler, @InitBinder, and @ModelAttribute annotated methods, and these methods will apply to @RequestMapping methods across all controller hierarchies as opposed to the controller hierarchy within which they are declared.

@RestControllerAdvice is an alternative where @ExceptionHandler methods assume @ResponseBody semantics by default.

Both @ControllerAdvice and @RestControllerAdvice can target a subset of controllers:

// Target all Controllers annotated with @RestController
@ControllerAdvice(annotations = RestController.class)
public class AnnotationAdvice {}

// Target all Controllers within specific packages
@ControllerAdvice("org.example.controllers")
public class BasePackageAdvice {}

// Target all Controllers assignable to specific classes
@ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class})
public class AssignableTypesAdvice {}

See the {api-spring-framework}/web/bind/annotation/ControllerAdvice.html[@ControllerAdvice] javadoc for more details.

URI Links

Spring MVC provides a mechanism for building and encoding a URI using UriComponentsBuilder and UriComponents.

For example you can expand and encode a URI template string:

UriComponents uriComponents = UriComponentsBuilder.fromUriString(
		"http://example.com/hotels/{hotel}/bookings/{booking}").build();

URI uri = uriComponents.expand("42", "21").encode().toUri();

Note that UriComponents is immutable and the expand() and encode() operations return new instances if necessary.

You can also expand and encode using individual URI components:

UriComponents uriComponents = UriComponentsBuilder.newInstance()
		.scheme("http").host("example.com").path("/hotels/{hotel}/bookings/{booking}").build()
		.expand("42", "21")
		.encode();

In a Servlet environment the ServletUriComponentsBuilder subclass provides static factory methods to copy available URL information from a Servlet requests:

HttpServletRequest request = ...

// Re-use host, scheme, port, path and query string
// Replace the "accountId" query param

ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request)
		.replaceQueryParam("accountId", "{id}").build()
		.expand("123")
		.encode();

Alternatively, you may choose to copy a subset of the available information up to and including the context path:

// Re-use host, port and context path
// Append "/accounts" to the path

ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request)
		.path("/accounts").build()

Or in cases where the DispatcherServlet is mapped by name (e.g. /main/*), you can also have the literal part of the servlet mapping included:

// Re-use host, port, context path
// Append the literal part of the servlet mapping to the path
// Append "/accounts" to the path

ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request)
		.path("/accounts").build()

Tip

Both ServletUriComponentsBuilder and MvcUriComponentsBuilder detect, extract, and use information from the "Forwarded" header, or from "X-Forwarded-Host", "X-Forwarded-Port", and "X-Forwarded-Proto" if "Forwarded" is not present, so that the resulting links reflect the original request. Note that you can also use the ForwardedHeaderFilter to the same once, globally.

Links to Controllers

Spring MVC also provides a mechanism for building links to controller methods. For example, given:

@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();

Links in views

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.

Exception Handling

Overview

Spring HandlerExceptionResolver implementations deal with unexpected exceptions that occur during controller execution. A HandlerExceptionResolver somewhat resembles the exception mappings you can define in the web application descriptor web.xml. However, they provide a more flexible way to do so. For example they provide information about which handler was executing when the exception was thrown. Furthermore, a programmatic way of handling exceptions gives you more options for responding appropriately before the request is forwarded to another URL (the same end result as when you use the Servlet specific exception mappings).

Besides implementing the HandlerExceptionResolver interface, which is only a matter of implementing the resolveException(Exception, Handler) method and returning a ModelAndView, you may also use the provided SimpleMappingExceptionResolver or create @ExceptionHandler methods. The SimpleMappingExceptionResolver enables you to take the class name of any exception that might be thrown and map it to a view name. This is functionally equivalent to the exception mapping feature from the Servlet API, but it is also possible to implement more finely grained mappings of exceptions from different handlers. The @ExceptionHandler annotation on the other hand can be used on methods that should be invoked to handle an exception. Such methods may be defined locally within an @Controller or may apply to many @Controller classes when defined within an @ControllerAdvice class. The following sections explain this in more detail.

@ExceptionHandler

The HandlerExceptionResolver interface and the SimpleMappingExceptionResolver implementations allow you to map Exceptions to specific views declaratively along with some optional Java logic before forwarding to those views. However, in some cases, especially when relying on @ResponseBody methods rather than on view resolution, it may be more convenient to directly set the status of the response and optionally write error content to the body of the response.

You can do that with @ExceptionHandler methods. When declared within a controller such methods apply to exceptions raised by @RequestMapping methods of that controller (or any of its subclasses). You can also declare an @ExceptionHandler method within an @ControllerAdvice class in which case it handles exceptions from @RequestMapping methods from many controllers. Below is an example of a controller-local @ExceptionHandler method:

@Controller
public class SimpleController {

	// @RequestMapping methods omitted ...

	@ExceptionHandler(IOException.class)
	public ResponseEntity<String> handleIOException(IOException ex) {
		// prepare responseEntity
		return responseEntity;
	}

}

The @ExceptionHandler value can be set to an array of Exception types. If an exception is thrown that matches one of the types in the list, then the method annotated with the matching @ExceptionHandler will be invoked. If the annotation value is not set then the exception types listed as method arguments are used.

Tip

For @ExceptionHandler methods, a root exception match will be preferred to just matching a cause of the current exception, among the handler methods of a particular controller or advice bean. However, a cause match on a higher-priority @ControllerAdvice will still be preferred to a any match (whether root or cause level) on a lower-priority advice bean. As a consequence, when using a multi-advice arrangement, please declare your primary root exception mappings on a prioritized advice bean with a corresponding order!

Much like standard controller methods annotated with a @RequestMapping annotation, the method arguments and return values of @ExceptionHandler methods can be flexible. For example, the HttpServletRequest can be accessed in Servlet environments. The return type can be a String, which is interpreted as a view name, a ModelAndView object, a ResponseEntity, or you can also add the @ResponseBody to have the method return value converted with message converters and written to the response stream.

Framework exceptions

Spring MVC may raise a number of exceptions while processing a request. The SimpleMappingExceptionResolver can easily map any exception to a default error view as needed. However, when working with clients that interpret responses in an automated way you will want to set specific status code on the response. Depending on the exception raised the status code may indicate a client error (4xx) or a server error (5xx).

The DefaultHandlerExceptionResolver translates Spring MVC exceptions to specific error status codes. It is registered by default with the MVC namespace, the MVC Java config, and also by the DispatcherServlet (i.e. when not using the MVC namespace or Java config). Listed below are some of the exceptions handled by this resolver and the corresponding status codes:

Exception	HTTP Status Code
BindException	400 (Bad Request)
ConversionNotSupportedException	500 (Internal Server Error)
HttpMediaTypeNotAcceptableException	406 (Not Acceptable)
HttpMediaTypeNotSupportedException	415 (Unsupported Media Type)
HttpMessageNotReadableException	400 (Bad Request)
HttpMessageNotWritableException	500 (Internal Server Error)
HttpRequestMethodNotSupportedException	405 (Method Not Allowed)
MethodArgumentNotValidException	400 (Bad Request)
MissingPathVariableException	500 (Internal Server Error)
MissingServletRequestParameterException	400 (Bad Request)
MissingServletRequestPartException	400 (Bad Request)
NoHandlerFoundException	404 (Not Found)
NoSuchRequestHandlingMethodException	404 (Not Found)
TypeMismatchException	400 (Bad Request)

The DefaultHandlerExceptionResolver works transparently by setting the status of the response. However, it stops short of writing any error content to the body of the response while your application may need to add developer-friendly content to every error response for example when providing a REST API. You can prepare a ModelAndView and render error content through view resolution — i.e. by configuring a ContentNegotiatingViewResolver, MappingJackson2JsonView, and so on. However, you may prefer to use @ExceptionHandler methods instead.

If you prefer to write error content via @ExceptionHandler methods you can extend ResponseEntityExceptionHandler instead. This is a convenient base for @ControllerAdvice classes providing an @ExceptionHandler method to handle standard Spring MVC exceptions and return ResponseEntity. That allows you to customize the response and write error content with message converters. See the ResponseEntityExceptionHandler javadocs for more details.

REST API exceptions

An @RestController may use @ExceptionHandler methods that return a ResponseEntity to provide both a response status and error details in the body of the response. Such methods may also be added to @ControllerAdvice classes for exception handling across a subset or all controllers.

A common requirement is to include error details in the body of the response. Spring does not automatically do this (although Spring Boot does) because the representation of error details in the response body is application specific.

Applications that wish to implement a global exception handling strategy with error details in the response body should consider extending the abstract base class ResponseEntityExceptionHandler which provides handling for the exceptions that Spring MVC raises and provides hooks to customize the response body as well as to handle other exceptions. Simply declare the extension class as a Spring bean and annotate it with @ControllerAdvice. For more details see See ResponseEntityExceptionHandler.

Annotated Exception

A business exception can be annotated with @ResponseStatus. When the exception is raised, the ResponseStatusExceptionResolver handles it by setting the status of the response accordingly. By default the DispatcherServlet registers the ResponseStatusExceptionResolver and it is available for use.

Container error page

When the status of the response is set to an error status code and the body of the response is empty, Servlet containers commonly render an HTML formatted error page. To customize the default error page of the container, you can declare an <error-page> element in web.xml. Up until Servlet 3, that element had to be mapped to a specific status code or exception type. Starting with Servlet 3 an error page does not need to be mapped, which effectively means the specified location customizes the default Servlet container error page.

<error-page>
	<location>/error</location>
</error-page>

Note that the actual location for the error page can be a JSP page or some other URL within the container including one handled through an @Controller method:

When writing error information, the status code and the error message set on the HttpServletResponse can be accessed through request attributes in a controller:

@Controller
public class ErrorController {

	@RequestMapping(path = "/error", produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
	@ResponseBody
	public Map<String, Object> handle(HttpServletRequest request) {

		Map<String, Object> map = new HashMap<String, Object>();
		map.put("status", request.getAttribute("javax.servlet.error.status_code"));
		map.put("reason", request.getAttribute("javax.servlet.error.message"));

		return map;
	}

}

or in a JSP:

<%@ page contentType="application/json" pageEncoding="UTF-8"%>
{
	status:<%=request.getAttribute("javax.servlet.error.status_code") %>,
	reason:<%=request.getAttribute("javax.servlet.error.message") %>
}

Async Requests

Processing

Spring MVC 3.2 introduced Servlet 3 based asynchronous request processing. Instead of returning a value, as usual, a controller method can now return a java.util.concurrent.Callable and produce the return value from a Spring MVC managed thread. Meanwhile the main Servlet container thread is exited and released and allowed to process other requests. Spring MVC invokes the Callable in a separate thread with the help of a TaskExecutor and when the Callable returns, the request is dispatched back to the Servlet container to resume processing using the value returned by the Callable. Here is an example of such a controller method:

@PostMapping
public Callable<String> processUpload(final MultipartFile file) {

	return new Callable<String>() {
		public String call() throws Exception {
			// ...
			return "someView";
		}
	};

}

Another option is for the controller method to return an instance of DeferredResult. In this case the return value will also be produced from any thread, i.e. one that is not managed by Spring MVC. For example the result may be produced in response to some external event such as a JMS message, a scheduled task, and so on. Here is an example of such a controller method:

@RequestMapping("/quotes")
@ResponseBody
public DeferredResult<String> quotes() {
	DeferredResult<String> deferredResult = new DeferredResult<String>();
	// Save the deferredResult somewhere..
	return deferredResult;
}

// In some other thread...
deferredResult.setResult(data);

This may be difficult to understand without any knowledge of the Servlet 3.0 asynchronous request processing features. It would certainly help to read up on that. Here are a few basic facts about the underlying mechanism:

• A ServletRequest can be put in asynchronous mode by calling request.startAsync(). The main effect of doing so is that the Servlet, as well as any Filters, can exit but the response will remain open to allow processing to complete later.

• The call to request.startAsync() returns AsyncContext which can be used for further control over async processing. For example it provides the method dispatch, that is similar to a forward from the Servlet API except it allows an application to resume request processing on a Servlet container thread.

• The ServletRequest provides access to the current DispatcherType that can be used to distinguish between processing the initial request, an async dispatch, a forward, and other dispatcher types.

With the above in mind, the following is the sequence of events for async request processing with a Callable:

• Controller returns a Callable.

• Spring MVC starts asynchronous processing and submits the Callable to a TaskExecutor for processing in a separate thread.

• The DispatcherServlet and all Filter’s exit the Servlet container thread but the response remains open.

• The Callable produces a result and Spring MVC dispatches the request back to the Servlet container to resume processing.

• The DispatcherServlet is invoked again and processing resumes with the asynchronously produced result from the Callable.

The sequence for DeferredResult is very similar except it’s up to the application to produce the asynchronous result from any thread:

• Controller returns a DeferredResult and saves it in some in-memory queue or list where it can be accessed.

• Spring MVC starts async processing.

• The DispatcherServlet and all configured Filter’s exit the request processing thread but the response remains open.

• The application sets the DeferredResult from some thread and Spring MVC dispatches the request back to the Servlet container.

• The DispatcherServlet is invoked again and processing resumes with the asynchronously produced result.

For further background on the motivation for async request processing and when or why to use it please read this blog post series.

Exception handling

What happens if a Callable returned from a controller method raises an Exception while being executed? The short answer is the same as what happens when a controller method raises an exception. It goes through the regular exception handling mechanism. The longer explanation is that when a Callable raises an Exception Spring MVC dispatches to the Servlet container with the Exception as the result and that leads to resume request processing with the Exception instead of a controller method return value. When using a DeferredResult you have a choice whether to call setResult or setErrorResult with an Exception instance.

Async interceptors

A HandlerInterceptor can also implement AsyncHandlerInterceptor in order to implement the afterConcurrentHandlingStarted callback, which is called instead of postHandle and afterCompletion when asynchronous processing starts.

A HandlerInterceptor can also register a CallableProcessingInterceptor or a DeferredResultProcessingInterceptor in order to integrate more deeply with the lifecycle of an asynchronous request and for example handle a timeout event. See the Javadoc of AsyncHandlerInterceptor for more details.

The DeferredResult type also provides methods such as onTimeout(Runnable) and onCompletion(Runnable). See the Javadoc of DeferredResult for more details.

When using a Callable you can wrap it with an instance of WebAsyncTask which also provides registration methods for timeout and completion.

Streaming response

A controller method can use DeferredResult and Callable to produce its return value asynchronously and that can be used to implement techniques such as long polling where the server can push an event to the client as soon as possible.

What if you wanted to push multiple events on a single HTTP response? This is a technique related to "Long Polling" that is known as "HTTP Streaming". Spring MVC makes this possible through the ResponseBodyEmitter return value type which can be used to send multiple Objects, instead of one as is normally the case with @ResponseBody, where each Object sent is written to the response with an HttpMessageConverter.

Here is an example of that:

@RequestMapping("/events")
public ResponseBodyEmitter 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();

Note that ResponseBodyEmitter can also be used as the body in a ResponseEntity in order to customize the status and headers of the response.

Server-Sent Events

SseEmitter is a subclass of ResponseBodyEmitter providing support for Server-Sent Events. Server-sent events is a just another variation on the same "HTTP Streaming" technique except events pushed from the server are formatted according to the W3C Server-Sent Events specification.

Server-Sent Events can be used for their intended purpose, that is to push events from the server to clients. It is quite easy to do in Spring MVC and requires simply returning a value of type SseEmitter.

Note however that Internet Explorer does not support Server-Sent Events and that for more advanced web application messaging scenarios such as online games, collaboration, financial applicatinos, and others it’s better to consider Spring’s WebSocket support that includes SockJS-style WebSocket emulation falling back to a very wide range of browsers (including Internet Explorer) and also higher-level messaging patterns for interacting with clients through a publish-subscribe model within a more messaging-centric architecture. For further background on this see the following blog post.

Streaming raw data

ResponseBodyEmitter allows sending events by writing Objects to the response through an HttpMessageConverter. This is probably the most common case, for example when writing JSON data. However sometimes it is useful to bypass message conversion and write directly to the response OutputStream for example for a file download. This can be done with the help of the StreamingResponseBody return value type.

Here is an example of that:

@RequestMapping("/download")
public StreamingResponseBody handle() {
	return new StreamingResponseBody() {
		@Override
		public void writeTo(OutputStream outputStream) throws IOException {
			// write...
		}
	};
}

Note that StreamingResponseBody can also be used as the body in a ResponseEntity in order to customize the status and headers of the response.

Reactive return values

If using the reactive WebClient from spring-webflux, or another client, or a data store with reactive support, you can return reactive types directly from Spring MVC controller methods.

Spring MVC adapts transparently to the reactive library in use with proper translation of cardinality — i.e. how many values are expected. This is done with the help of the {api-spring-framework}/core/ReactiveAdapterRegistry.html[ReactiveAdapterRegistry] from spring-core which provides pluggable support for reactive and async types. The registry has built-in support for RxJava but others can be registered.

Return values are handled as follows:

• If the return type has single-value stream semantics such as Reactor Mono or RxJava Single it is adapted and equivalent to using DeferredResult.

• If the return type has multi-value stream semantics such as Reactor Flux or RxJava Observable / Flowable and if the media type indicates streaming, e.g. "application/stream+json" or "text/event-stream", it is adapted and equivalent to using ResponseBodyEmitter or SseEmitter. You can also return Flux<ServerSentEvent> or Observable<ServerSentEvent>.

• If the return type has multi-value stream semantics but the media type does not imply streaming, e.g. "application/json", it is adapted and equivalent to using DeferredResult<List<?>>, e.g. JSON array.

Reactive libraries are detected and adapted to a Reactive Streams Publisher through Spring’s pluggable ReactiveAdapterRegistry which by default supports Reactor 3, RxJava 2, and RxJava 1. Note that for RxJava 1 you will need to add "io.reactivex:rxjava-reactive-streams" to the classpath.

A common assumption with reactive libraries is to not block the processing thread. The WebClient with Reactor Netty for example is based on event-loop style handling using a small, fixed number of threads and those must not be blocked when writing to the ServletResponseOutputStream. Reactive libraries have operators for that but Spring MVC automatically writes asynchronously so you don’t need to use them. The underlying TaskExecutor for this must be configured through the MVC Java config and the MVC namespace as described in the following section which by default is a SyncTaskExecutor and hence not suitable for production use.

Note	Unlike Spring MVC, Spring WebFlux is built on a non-blocking, reactive foundation and uses the Servlet 3.1 non-blocking I/O that’s also based on event loop style processing and hence does not require a thread to absorb the effect of blocking.

Configuration

For asynchronous requests there are minor requirements at the Servlet container level and more controls in Spring MVC configuration.

Servlet container config

For applications configured with a web.xml be sure to update to version 3.0:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
			http://java.sun.com/xml/ns/javaee
			http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">

	...

</web-app>

Asynchronous support must be enabled on the DispatcherServlet through the <async-supported>true</async-supported> sub-element in web.xml. Additionally any Filter that participates in asyncrequest processing must be configured to support the ASYNC dispatcher type. It should be safe to enable the ASYNC dispatcher type for all filters provided with the Spring Framework since they usually extend OncePerRequestFilter and that has runtime checks for whether the filter needs to be involved in async dispatches or not.

Below is some example web.xml configuration:

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
			http://java.sun.com/xml/ns/javaee
			http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
	version="3.0">

	<filter>
		<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
		<filter-class>org.springframework.~.OpenEntityManagerInViewFilter</filter-class>
		<async-supported>true</async-supported>
	</filter>

	<filter-mapping>
		<filter-name>Spring OpenEntityManagerInViewFilter</filter-name>
		<url-pattern>/*</url-pattern>
		<dispatcher>REQUEST</dispatcher>
		<dispatcher>ASYNC</dispatcher>
	</filter-mapping>

</web-app>

If using Servlet 3, Java based configuration for example via WebApplicationInitializer, you’ll also need to set the "asyncSupported" flag as well as the ASYNC dispatcher type just like with web.xml. To simplify all this configuration, consider extending AbstractDispatcherServletInitializer, or better AbstractAnnotationConfigDispatcherServletInitializer which automatically set those options and make it very easy to register Filter instances.

Spring MVC config

The MVC Java config and the MVC namespace provide options for configuring asynchronous request processing. WebMvcConfigurer has the method configureAsyncSupport while <mvc:annotation-driven> has an <async-support> sub-element.

Those allow you to configure the default timeout value to use for async requests, which if not set depends on the underlying Servlet container (e.g. 10 seconds on Tomcat). You can also configure an AsyncTaskExecutor to use for executing Callable instances returned from controller methods. It is highly recommended to configure this property since by default Spring MVC uses SimpleAsyncTaskExecutor. The MVC Java config and the MVC namespace also allow you to register CallableProcessingInterceptor and DeferredResultProcessingInterceptor instances.

If you need to override the default timeout value for a specific DeferredResult, you can do so by using the appropriate class constructor. Similarly, for a Callable, you can wrap it in a WebAsyncTask and use the appropriate class constructor to customize the timeout value. The class constructor of WebAsyncTask also allows providing an AsyncTaskExecutor.

webmvc-cors.adoc

Web Security

The Spring Security project provides features to protect web applications from malicious exploits. Check out the reference documentation in the sections on {doc-root}/spring-security/site/docs/current/reference/htmlsingle/#csrf["CSRF protection"], {doc-root}/spring-security/site/docs/current/reference/htmlsingle/#headers["Security Response Headers"], and also {doc-root}/spring-security/site/docs/current/reference/htmlsingle/#mvc["Spring MVC Integration"]. Note that using Spring Security to secure the application is not necessarily required for all features. For example CSRF protection can be added simply by adding the CsrfFilter and CsrfRequestDataValueProcessor to your configuration. See the Spring MVC Showcase for an example.

Another option is to use a framework dedicated to Web Security. HDIV is one such framework and integrates with Spring MVC.

The Model ModelMap (ModelAndView)

The ModelMap class is essentially a glorified Map that can make adding objects that are to be displayed in (or on) a View adhere to a common naming convention. Consider the following Controller implementation; notice that objects are added to the ModelAndView without any associated name specified.

public class DisplayShoppingCartController implements Controller {

	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {

		List cartItems = // get a List of CartItem objects
		User user = // get the User doing the shopping

		ModelAndView mav = new ModelAndView("displayShoppingCart"); <-- the logical view name

		mav.addObject(cartItems); <-- look ma, no name, just the object
		mav.addObject(user); <-- and again ma!

		return mav;
	}
}

The ModelAndView class uses a ModelMap class that is a custom Map implementation that automatically generates a key for an object when an object is added to it. The strategy for determining the name for an added object is, in the case of a scalar object such as User, to use the short class name of the object’s class. The following examples are names that are generated for scalar objects put into a ModelMap instance.

• An x.y.User instance added will have the name user generated.

• An x.y.Registration instance added will have the name registration generated.

• An x.y.Foo instance added will have the name foo generated.

• A java.util.HashMap instance added will have the name hashMap generated. You probably want to be explicit about the name in this case because hashMap is less than intuitive.

• Adding null will result in an IllegalArgumentException being thrown. If the object (or objects) that you are adding could be null, then you will also want to be explicit about the name.

What, no automatic pluralization?

Spring Web MVC’s convention-over-configuration support does not support automatic pluralization. That is, you cannot add a List of Person objects to a ModelAndView and have the generated name be people.

This decision was made after some debate, with the "Principle of Least Surprise" winning out in the end.

The strategy for generating a name after adding a Set or a List is to peek into the collection, take the short class name of the first object in the collection, and use that with List appended to the name. The same applies to arrays although with arrays it is not necessary to peek into the array contents. A few examples will make the semantics of name generation for collections clearer:

• An x.y.User[] array with zero or more x.y.User elements added will have the name userList generated.

• An x.y.Foo[] array with zero or more x.y.User elements added will have the name fooList generated.

• A java.util.ArrayList with one or more x.y.User elements added will have the name userList generated.

• A java.util.HashSet with one or more x.y.Foo elements added will have the name fooList generated.

• An empty java.util.ArrayList will not be added at all (in effect, the addObject(..) call will essentially be a no-op).

Default view name

The RequestToViewNameTranslator interface determines a logical View name when no such logical view name is explicitly supplied. It has just one implementation, the DefaultRequestToViewNameTranslator class.

The DefaultRequestToViewNameTranslator maps request URLs to logical view names, as with this example:

public class RegistrationController implements Controller {

	public ModelAndView handleRequest(HttpServletRequest request, HttpServletResponse response) {
		// process the request...
		ModelAndView mav = new ModelAndView();
		// add data as necessary to the model...
		return mav;
		// notice that no View or logical view name has been set
	}

}

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
	xsi:schemaLocation="
		http://www.springframework.org/schema/beans
		http://www.springframework.org/schema/beans/spring-beans.xsd">

	<!-- this bean with the well known name generates view names for us -->
	<bean id="viewNameTranslator"
			class="org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator"/>

	<bean class="x.y.RegistrationController">
		<!-- inject dependencies as necessary -->
	</bean>

	<!-- maps request URLs to Controller names -->
	<bean class="org.springframework.web.servlet.mvc.support.ControllerClassNameHandlerMapping"/>

	<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
		<property name="prefix" value="/WEB-INF/jsp/"/>
		<property name="suffix" value=".jsp"/>
	</bean>

</beans>

Notice how in the implementation of the handleRequest(..) method no View or logical view name is ever set on the ModelAndView that is returned. The DefaultRequestToViewNameTranslator is tasked with generating a logical view name from the URL of the request. In the case of the above RegistrationController, which is used in conjunction with the ControllerClassNameHandlerMapping, a request URL of http://localhost/registration.html results in a logical view name of registration being generated by the DefaultRequestToViewNameTranslator. This logical view name is then resolved into the /WEB-INF/jsp/registration.jsp view by the InternalResourceViewResolver bean.

Tip	You do not need to define a DefaultRequestToViewNameTranslator bean explicitly. If you like the default settings of the DefaultRequestToViewNameTranslator, you can rely on the Spring Web MVC DispatcherServlet to instantiate an instance of this class if one is not explicitly configured.

Of course, if you need to change the default settings, then you do need to configure your own DefaultRequestToViewNameTranslator bean explicitly. Consult the comprehensive DefaultRequestToViewNameTranslator javadocs for details on the various properties that can be configured.

HTTP Caching

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.

Cache-Control

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 -1 value won’t generate a 'Cache-Control' response header.

• A 0 value will prevent caching using the 'Cache-Control: no-store' directive.

• An n > 0 value will cache the given response for n seconds 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

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>

@Controller caching

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.

ETag Filter

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.

MVC Config

Same in Spring WebFlux

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 Framework Config.

Enable MVC Config

Same in Spring WebFlux

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.

MVC Config API

Same in Spring WebFlux

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.

Type conversion

Same in Spring WebFlux

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 FormattingConversionServiceFactoryBean for more information on when to use FormatterRegistrars.

Validation

Same in Spring WebFlux

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 LocalValidatorFactoryBean injected somewhere, create a bean and mark it with @Primary in order to avoid conflict with the one declared in the MVC config.

Interceptors

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>

Content Types

Same in Spring WebFlux

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>

Message Converters

Same in Spring WebFlux

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:

1. DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES is disabled.

2. MapperFeature.DEFAULT_VIEW_INCLUSION is disabled.

It also automatically registers the following well-known modules if they are detected on the classpath:

1. jackson-datatype-jdk7: support for Java 7 types like java.nio.file.Path.

2. jackson-datatype-joda: support for Joda-Time types.

3. jackson-datatype-jsr310: support for Java 8 Date & Time API types.

4. jackson-datatype-jdk8: support for other Java 8 types like Optional.

Note	Enabling indentation with Jackson XML support requires woodstox-core-asl dependency in addition to jackson-dataformat-xml one.

Other interesting Jackson modules are available:

1. jackson-datatype-money: support for javax.money types (unofficial module)

2. 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"/>

View Controllers

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"/>

View Resolvers

Same in Spring WebFlux

The MVC config simplifies the registration of view resolvers.

The following is a Java config example that configures content negotiation view resolution using FreeMarker HTML templates and Jackson as a default View for JSON rendering:

@Configuration
@EnableWebMvc
public class WebConfig 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;
	}
}

Static Resources

Same in Spring WebFlux

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" />

See also HTTP caching support for static resources.

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[ResourceResolver]'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".

Default Servlet

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"/>

Path Matching

Same in Spring WebFlux

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"/>

Advanced Java Config

Same in Spring WebFlux

@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.

Advanced XML Config

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.

webmvc-view.adoc

HTTP/2

Same in Spring WebFlux

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.