Spring Web MVC is the original web framework built on the Servlet API and has been 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, see the Spring Framework Wiki.
Spring MVC, as 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 by 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.
The following example of the Java configuration registers and initializes
the DispatcherServlet, which is auto-detected by the Servlet container
(see Servlet Config):
public class MyWebApplicationInitializer implements WebApplicationInitializer {
@Override
public void onStartup(ServletContext servletCxt) {
// Load Spring web application configuration
AnnotationConfigWebApplicationContext ac = new AnnotationConfigWebApplicationContext();
ac.register(AppConfig.class);
ac.refresh();
// Create and register the DispatcherServlet
DispatcherServlet servlet = new DispatcherServlet(ac);
ServletRegistration.Dynamic registration = servletCxt.addServlet("app", servlet);
registration.setLoadOnStartup(1);
registration.addMapping("/app/*");
}
}|
Note
|
In addition to using the ServletContext API directly, you can also extend
AbstractAnnotationConfigDispatcherServletInitializer and override specific methods
(see the example under Context Hierarchy).
|
The following example of web.xml configuration registers and initializes 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, see the
Spring Boot documentation.
|
DispatcherServlet expects a WebApplicationContext (an extension of a plain
ApplicationContext) for its own configuration. WebApplicationContext has a link to the
ServletContext and the Servlet with which it is associated. 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 suffices.
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 can be overridden (that is, re-declared) in the Servlet-specific
child WebApplicationContext, which typically contains beans local to the given Servlet.
The following image shows this relationship:
The following example configures 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 can return all
configuration through getRootConfigClasses() and null from getServletConfigClasses().
|
The following example shows 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.
|
The DispatcherServlet delegates to special beans to process requests and render the
appropriate responses. By “special beans” we mean Spring-managed Object instances that
implement WebFlux framework contracts. Those usually come with built-in contracts, but
you can customize their properties and extend or replace them.
The following table lists the special beans detected by the DispatcherHandler:
| Bean type | Explanation |
|---|---|
|
Map a request to a handler along with a list of
interceptors for pre- and post-processing.
The mapping is based on some criteria, the details of which vary by The two main |
|
Help the |
Strategy to resolve exceptions, possibly mapping them to handlers, to HTML error views, or other targets. See Exceptions. |
|
Resolve logical |
|
Resolve the |
|
Resolve themes your web application can use — for example, to offer personalized layouts. See Themes. |
|
Abstraction for parsing a multi-part request (for example, browser form file upload) with the help of some multipart parsing library. See Multipart Resolver. |
|
Store and retrieve the “input” and the “output” |
Applications can declare the infrastructure beans listed in Special Bean Types
that are required to process requests. The DispatcherServlet checks the
WebApplicationContext for each special bean. If there are no matching bean types,
it falls back on the default types listed in
DispatcherServlet.properties.
In most cases, the MVC Config is the best starting point. It declares the required beans in either Java or XML and provides a higher-level configuration callback API to customize it.
|
Note
|
Spring Boot relies on the MVC Java configuration to configure Spring MVC and provides many extra convenient options. |
In a Servlet 3.0+ environment, you have the option of configuring the Servlet container
programmatically as an alternative or in combination with a web.xml file. The following
example registers 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 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, as the following example shows:
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 you use XML-based Spring configuration, you should extend directly from
AbstractDispatcherServletInitializer, as the following example shows:
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 be automatically mapped to the DispatcherServlet, as the
following example shows:
public class MyWebAppInitializer extends AbstractDispatcherServletInitializer {
// ...
@Override
protected Filter[] getServletFilters() {
return new Filter[] {
new HiddenHttpMethodFilter(), new CharacterEncodingFilter() };
}
}Each filter is added with a default name based on its concrete type and automatically
mapped to the DispatcherServlet.
The isAsyncSupported protected method of AbstractDispatcherServletInitializer
provides a single place to enable async support on the DispatcherServlet and all
filters mapped to it. By default, this flag is set to true.
Finally, if you need to further customize the DispatcherServlet itself, you can
override the createDispatcherServlet method.
The DispatcherServlet processes requests as follows:
-
The
WebApplicationContextis searched for and bound in the request as an attribute that the controller and other elements in the process can use. It is bound by default under theDispatcherServlet.WEB_APPLICATION_CONTEXT_ATTRIBUTEkey. -
The locale resolver is bound to the request to let elements in the process 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 the locale resolver.
-
The theme resolver is bound to the request to let elements such as views determine which theme to use. If you do not use themes, you can ignore it.
-
If you specify a multipart file resolver, the request is inspected for multiparts. If multiparts are found, the request is wrapped in a
MultipartHttpServletRequestfor further processing by other elements in the process. See Multipart Resolver for further information about multipart handling. -
An appropriate handler is searched for. If a handler is found, the execution chain associated with the handler (preprocessors, postprocessors, and controllers) is executed in order to prepare a model or rendering. Alternatively, for annotated controllers, the response can be rendered (within the
HandlerAdapter) instead of returning a view. -
If a model is returned, the view is rendered. If no model is returned (maybe due to a preprocessor or postprocessor intercepting the request, perhaps for security reasons), no view is rendered, because the request could already have been fulfilled.
The HandlerExceptionResolver beans declared in the WebApplicationContext are used to
resolve exceptions thrown during request processing. Those exception resolvers allow
customizing the logic to address exceptions. See Exceptions for more details.
The Spring DispatcherServlet also supports the return of the
last-modification-date, as specified by the Servlet API. The process of determining
the last modification date for a specific request is straightforward: The
DispatcherServlet looks up an appropriate handler mapping and tests whether the
handler that is found implements the LastModified interface. If so, the value of the
long getLastModified(request) method of the LastModified interface is returned to
the client.
You can customize individual DispatcherServlet instances by adding Servlet
initialization parameters (init-param elements) to the Servlet declaration in the
web.xml file. The following table lists the supported parameters:
| Parameter | Explanation |
|---|---|
|
Class that implements |
|
String that is passed to the context instance (specified by |
|
Namespace of the |
|
Whether to throw a By default, this is set to Note that, if default servlet handling is also configured, unresolved requests are always forwarded to the default servlet and a 404 is never raised. |
All HandlerMapping implementations support 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 continues. 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 by using setters on individual
HandlerMapping implementations.
Note that postHandle is less useful with @ResponseBody and ResponseEntity methods for
which the response is written and committed within the HandlerAdapter and before
postHandle. That means it is too late to make any changes to the response, such as adding
an extra header. For such scenarios, you can implement ResponseBodyAdvice and either
declare it as an Controller Advice bean or configure it directly on
RequestMappingHandlerAdapter.
If an exception occurs during request mapping or is thrown from a request handler (such as
a @Controller), the DispatcherServlet delegates to a chain of HandlerExceptionResolver
beans to resolve the exception and provide alternative handling, which is typically an
error response.
The following table lists the available HandlerExceptionResolver implementations:
HandlerExceptionResolver |
Description |
|---|---|
|
A mapping between exception class names and error view names. Useful for rendering error pages in a browser application. |
{api-spring-framework}/web/servlet/mvc/support/DefaultHandlerExceptionResolver.html[ |
Resolves exceptions raised by Spring MVC and maps them to HTTP status codes.
See also alternative |
|
Resolves exceptions with the |
|
Resolves exceptions by invoking an |
You can form an exception resolver chain by declaring multiple HandlerExceptionResolver
beans in your Spring configuration and setting their order properties as needed.
The higher the order property, the later the exception resolver is positioned.
The contract of HandlerExceptionResolver specifies that it can return:
-
a
ModelAndViewthat points to an error view. -
An empty
ModelAndViewif the exception was handled within the resolver. -
nullif the exception remains unresolved, for subsequent resolvers to try, and, if the exception remains at the end, it is allowed to bubble up to the Servlet container.
The MVC Config automatically declares built-in resolvers for default Spring MVC
exceptions, for @ResponseStatus annotated exceptions, and for support of
@ExceptionHandler methods. You can customize that list or replace it.
If an exception remains unresolved by any HandlerExceptionResolver and is, therefore,
left to propagate or if the response status is set to an error status (that is, 4xx, 5xx),
Servlet containers ca render a default error page in HTML. To customize the default
error page of the container, you can declare an error page mapping in web.xml.
The following example shows how to do so:
<error-page>
<location>/error</location>
</error-page>Given the preceding example, when an exception bubbles up or the response has an error status, the
Servlet container makes an ERROR dispatch within the container to the configured URL
(for example, /error). This is then processed by the DispatcherServlet, possibly mapping it
to a @Controller, which could be implemented to return an error view name with a model
or to render a JSON response, as the following example shows:
@RestController
public class ErrorController {
@RequestMapping(path = "/error")
public Map<String, Object> handle(HttpServletRequest request) {
Map<String, Object> map = new HashMap<String, Object>();
map.put("status", request.getAttribute("javax.servlet.error.status_code"));
map.put("reason", request.getAttribute("javax.servlet.error.message"));
return map;
}
}|
Tip
|
The Servlet API does not provide a way to create error page mappings in Java. You can,
however, use both a WebApplicationInitializer and a minimal web.xml.
|
Spring MVC defines the ViewResolver and View interfaces that let you render
models in a browser without tying you to a specific view technology. ViewResolver
provides a mapping between view names and actual views. View addresses the preparation
of data before handing over to a specific view technology.
The following table provides more details on the ViewResolver hierarchy:
| ViewResolver | Description |
|---|---|
|
Sub-classes of |
|
Implementation of |
|
Implementation of |
|
Simple implementation of the |
|
Convenient subclass of |
|
Convenient subclass of |
|
Implementation of the |
You can chain view resolvers by declaring more than one resolver bean and, if necessary, by
setting the order property to specify ordering. Remember, the higher the order property,
the later the view resolver is positioned in the chain.
The contract of a ViewResolver specifies that it can return null to indicate that the
view could not be found. However, in the case of JSPs and InternalResourceViewResolver,
the only way to figure out if a JSP exists is to perform a dispatch through
RequestDispatcher. Therefore, you must always configure an InternalResourceViewResolver
to be last in the overall order of view resolvers.
Configuring view resolution is as simple as adding ViewResolver beans to your Spring
configuration. The MVC Config provides a dedicated configuration API for
View Resolvers and for adding logic-less
View Controllers which are useful for HTML template
rendering without controller logic.
The special redirect: prefix in a view name lets you perform a redirect. The
UrlBasedViewResolver (and its subclasses) recognize this as an instruction that a
redirect is needed. The rest of the view name is the redirect URL.
The net effect is the same as if the controller had returned a RedirectView, but now
the controller itself can operate in terms of logical view names. A logical view
name (such as redirect:/myapp/some/resource) redirects relative to the current
Servlet context, while a name such as redirect:http://myhost.com/some/arbitrary/path
redirects 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.
You can also 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 you use another view
technology but still want to force a forward of a resource to be handled by the
Servlet/JSP engine. Note that you may also chain multiple view resolvers, instead.
{api-spring-framework}/web/servlet/view/ContentNegotiatingViewResolver.html[ContentNegotiatingViewResolver]
does not resolve views itself but rather delegates
to other view resolvers and selects the view that resembles the representation requested
by the client. The representation can be determined from the Accept header or from a
query parameter (for example, "/path?format=pdf").
The ContentNegotiatingViewResolver selects an appropriate View to handle the request
by comparing the request media types 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,
the list of views specified through the DefaultViews property is 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 can include wildcards (for example text/*), in which case a View whose
Content-Type is text/xml is a compatible match.
See View Resolvers under MVC Config for configuration details.
Most parts of Spring’s architecture support internationalization, as the Spring web
MVC framework does. DispatcherServlet lets you automatically resolve messages
by 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. By 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. The following selection of locale resolvers is included in
Spring.
In addition to obtaining the client’s locale, it is often useful to know its time zone.
The LocaleContextResolver interface offers an extension to LocaleResolver that lets
resolvers provide a richer LocaleContext, which may include time zone information.
When available, the user’s TimeZone can be obtained by using the
RequestContext.getTimeZone() method. Time zone information is automatically used
by any Date/Time Converter and Formatter objects that are registered with Spring’s
ConversionService.
This locale resolver inspects the accept-language header in the request that was sent
by the client (for example, a web browser). Usually, this header field contains the locale of
the client’s operating system. Note that this resolver does not support time zone
information.
This locale resolver inspects a Cookie that might exist on the client to see if a
Locale or TimeZone is specified. If so, it uses the specified details. By using the
properties of this locale resolver, you can specify the name of the cookie as well as the
maximum age. The following example defines 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>The following table describes the properties CookieLocaleResolver:
| Property | Default | Description |
|---|---|---|
|
classname + LOCALE |
The name of the cookie |
|
Servlet container default |
The maximum time a cookie persists on the client. If |
|
/ |
Limits the visibility of the cookie to a certain part of your site. When |
The SessionLocaleResolver lets you 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 temporary
for each session and are, 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 evaluates and
modifies the corresponding HttpSession attributes against the current HttpServletRequest.
You can enable changing of locales by adding the LocaleChangeInterceptor to one of the
HandlerMapping definitions. It detects a parameter in the request and changes the locale
accordingly, calling the setLocale method on the LocaleResolver in the dispatcher’s
application context. The next example shows that calls to all *.view resources
that contain a parameter named siteLanguage now changes the locale. So, for example,
a request for the URL, http://www.sf.net/home.view?siteLanguage=nl, changes the site
language to Dutch. The following example shows how to intercept the locale:
<bean id="localeChangeInterceptor"
class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor">
<property name="paramName" value="siteLanguage"/>
</bean>
<bean id="localeResolver"
class="org.springframework.web.servlet.i18n.CookieLocaleResolver"/>
<bean id="urlMapping"
class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<property name="interceptors">
<list>
<ref bean="localeChangeInterceptor"/>
</list>
</property>
<property name="mappings">
<value>/**/*.view=someController</value>
</property>
</bean>You can apply Spring Web MVC framework themes to set the overall look-and-feel of your application, thereby enhancing user experience. A theme is a collection of static resources, typically style sheets and images, that affect the visual style of the application.
To use themes in your web application, you must set up an implementation of the
org.springframework.ui.context.ThemeSource interface. The WebApplicationContext
interface extends ThemeSource but delegates its responsibilities to a dedicated
implementation. By default, the delegate is 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 you use the ResourceBundleThemeSource, a theme is defined in a simple properties
file. The properties file lists the resources that make up the theme, as the following example shows:
styleSheet=/themes/cool/style.css background=/themes/cool/img/coolBg.jpg
The keys of the properties are the names that refer to the themed elements from view
code. For a JSP, you typically do this using the spring:theme custom tag, which is
very similar to the spring:message tag. The following JSP fragment uses the theme
defined in the previous example to customize the look and feel:
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%>
<html>
<head>
<link rel="stylesheet" href="<spring:theme code='styleSheet'/>" type="text/css"/>
</head>
<body style="background=<spring:theme code='background'/>">
...
</body>
</html>By default, the ResourceBundleThemeSource uses an empty base name prefix. As a result,
the properties files are loaded from the root of the classpath. Thus, you would put the
cool.properties theme definition in a directory at the root of the classpath (for
example, in /WEB-INF/classes). The ResourceBundleThemeSource uses the standard Java
resource bundle loading mechanism, allowing for full internationalization of themes. For
example, we could have a /WEB-INF/classes/cool_nl.properties that references a special
background image with Dutch text on it.
After you define themes, as described in the preceding section,
you decide which theme to use. The DispatcherServlet looks 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 table describes the theme resolvers provided by Spring:
| Class | Description |
|---|---|
|
Selects a fixed theme, set by using the |
|
The theme is maintained in the user’s HTTP session. It needs to be set only once for each session but is not persisted between sessions. |
|
The selected theme is stored in a cookie on the client. |
Spring also provides a ThemeChangeInterceptor that lets theme changes on every
request with a simple request parameter.
MultipartResolver from the org.springframework.web.multipart package is a strategy
for parsing multipart requests including file uploads. There is one implementation
based on Commons FileUpload and another
based on Servlet 3.0 multipart request parsing.
To enable multipart handling, you need to declare a MultipartResolver bean in your
DispatcherServlet Spring configuration with a name of multipartResolver.
The DispatcherServlet detects it and applies it to the incoming request. When a POST with
content-type of multipart/form-data is received, the resolver parses the content and
wraps the current HttpServletRequest as MultipartHttpServletRequest to
provide access to resolved parts in addition to exposing them as request parameters.
To use Apache Commons FileUpload, you can configure a bean of type
CommonsMultipartResolver with a name of multipartResolver. You also need to
have commons-fileupload as a dependency on your classpath.
Servlet 3.0 multipart parsing needs to be enabled through Servlet container configuration. To do so:
-
In Java, set a
MultipartConfigElementon the Servlet registration. -
In
web.xml, add a"<multipart-config>"section to the servlet declaration.
The following example shows how to set a MultipartConfigElement on the Servlet registration:
public class AppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
// ...
@Override
protected void customizeRegistration(ServletRegistration.Dynamic registration) {
// Optionally also set maxFileSize, maxRequestSize, fileSizeThreshold
registration.setMultipartConfig(new MultipartConfigElement("/tmp"));
}
}Once the Servlet 3.0 configuration is in place, you can add a bean of type
StandardServletMultipartResolver with a name of multipartResolver.
DEBUG-level logging in Spring MVC is designed to be compact, minimal, and human-friendly. It focuses on high-value bits of information that are useful over and over again versus others that are useful only when debugging a specific issue.
TRACE-level logging generally follows the same principles as DEBUG (and, for example, also should not be a fire hose) but can be used for debugging any issue. In addition, some log messages may show a different level of detail at TRACE versus DEBUG.
Good logging comes from the experience of using the logs. If you spot anything that does not meet the stated goals, please let us know.
DEBUG and TRACE logging may log sensitive information. This is why request parameters and
headers are masked by default and their logging in full must be enabled explicitly
through the enableLoggingRequestDetails property on DispatcherServlet.
The following example shows how to do so by using Java configuration:
public class MyInitializer
extends AbstractAnnotationConfigDispatcherServletInitializer {
@Override
protected Class<?>[] getRootConfigClasses() {
return ... ;
}
@Override
protected Class<?>[] getServletConfigClasses() {
return ... ;
}
@Override
protected String[] getServletMappings() {
return ... ;
}
@Override
protected void customizeRegistration(Dynamic registration) {
registration.setInitParameter("enableLoggingRequestDetails", "true");
}
}The spring-web module provides some useful filters:
Browsers can submit form data only through HTTP GET or HTTP POST but non-browser clients can also
use HTTP PUT, PATCH, and DELETE. The Servlet API requires ServletRequest.getParameter*()
methods to support form field access only for HTTP POST.
The spring-web module provides FormContentFilter to intercept HTTP PUT, PATCH, and DELETE
requests with a content type of application/x-www-form-urlencoded, read the form data from
the body of the request, and wrap the ServletRequest to make the form data
available through the ServletRequest.getParameter*() family of methods.
As a request goes through proxies (such as load balancers) the host, port, and scheme may change, and that makes it a challenge to create links that point to the correct host, port, and scheme from a client perspective.
RFC 7239 defines the Forwarded HTTP header
that proxies can use to provide information about the original request. There are other
non-standard headers, too, including X-Forwarded-Host, X-Forwarded-Port,
X-Forwarded-Proto, X-Forwarded-Ssl, and X-Forwarded-Prefix.
ForwardedHeaderFilter is a Servlet filter that modifies the host, port, and scheme of
the request, based on Forwarded headers, and then removes those headers.
There are security considerations for forwarded headers since an application cannot know
if the headers were added by a proxy, as intended, or by a malicious client. This is why
a proxy at the boundary of trust should be configured to remove untrusted Forwarded headers that come
from the outside. You can also configure the ForwardedHeaderFilter with
removeOnly=true, in which case it removes but does not use the headers.
The ShallowEtagHeaderFilter filter creates a “shallow” ETag by caching the content
written to the response and computing an MD5 hash from it. The next time a client sends,
it does the same, but it also compares the computed value against the If-None-Match request
header and, if the two are equal, returns a 304 (NOT_MODIFIED).
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 earlier, can avoid the computation. See HTTP Caching.
This filter has a writeWeakETag parameter that configures the filter to write weak ETags
similar to the following: W/"02a2d595e6ed9a0b24f027f2b63b134d6" (as defined in
RFC 7232 Section 2.3).
Spring MVC provides fine-grained support for CORS configuration through annotations on
controllers. However, when used with Spring Security, we advise relying on the built-in
CorsFilter that must be ordered ahead of Spring Security’s chain of filters.
See the sections on [mvc-cors] and the [mvc-cors-filter] for more details.
Spring MVC provides an annotation-based programming model where @Controller and
@RestController components use annotations to express request mappings, request input,
exception handling, and more. Annotated controllers have flexible method signatures and
do not have to extend base classes nor implement specific interfaces.
The following example shows a controller defined by annotations:
@Controller
public class HelloController {
@GetMapping("/hello")
public String handle(Model model) {
model.addAttribute("message", "Hello World!");
return "index";
}
}In the preceding example, the method accepts a Model and returns a view name as a String,
but many other options exist and are explained later in this chapter.
|
Tip
|
Guides and tutorials on spring.io use the annotation-based programming model described in this section. |
You can define controller beans by 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, as the following example shows:
@Configuration
@ComponentScan("org.example.web")
public class WebConfig {
// ...
}The following example shows the XML configuration equivalent of the preceding example:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="org.example.web"/>
<!-- ... -->
</beans>@RestController is a composed annotation that is
itself meta-annotated with @Controller and @ResponseBody to indicate a controller whose
every method inherits the type-level @ResponseBody annotation and, therefore, writes
directly to the response body versus view resolution and rendering with an HTML template.
In some cases, you many need to decorate a controller 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 (such as InitializingBean, *Aware, and others), you may need to explicitly
configure class-based proxying. For example, with <tx:annotation-driven/>, you can
change to <tx:annotation-driven proxy-target-class="true"/>.
You can use the @RequestMapping annotation to map requests to controllers methods. It has
various attributes to match by URL, HTTP method, request parameters, headers, and media
types. You can use it 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 shortcuts are Custom Annotations that are provided
because, arguably, most controller methods should be mapped to a specific HTTP method versus
using @RequestMapping, which, by default, matches to all HTTP methods. At the same, a
@RequestMapping is still needed at the class level to express shared mappings.
The following example has type and method level mappings:
@RestController
@RequestMapping("/persons")
class PersonController {
@GetMapping("/{id}")
public Person getPerson(@PathVariable Long id) {
// ...
}
@PostMapping
@ResponseStatus(HttpStatus.CREATED)
public void add(@RequestBody Person person) {
// ...
}
}You can map requests by using the following 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,
as the following example shows:
@GetMapping("/owners/{ownerId}/pets/{petId}")
public Pet findPet(@PathVariable Long ownerId, @PathVariable Long petId) {
// ...
}You can declare URI variables at the class and method levels, as the following example shows:
@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, and so on) are supported by default and you can
register support for any other data type.
See Type Conversion and DataBinder.
You can explicitly name URI variables (for example, @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 expression that has
syntax of {varName:regex}. For example, given URL "/spring-web-3.0.5 .jar", the following 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
by using PropertyPlaceHolderConfigurer against local, system, environment, and other property
sources. You can use this, 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.
|
When multiple patterns match a URL, they must be compared to find the best match. This is done
by using AntPathMatcher.getPatternComparator(String path), which looks for patterns that are 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 do not have double wildcards.
For the full details, see {api-spring-framework}/util/AntPathMatcher.AntPatternComparator.html[AntPatternComparator]
in {api-spring-framework}/util/AntPathMatcher.html[AntPathMatcher] and also keep mind that
you can customize the {api-spring-framework}/util/PathMatcher.html[PathMatcher] implementation.
See Path Matching in the configuration section.
By default, Spring MVC performs .* suffix pattern matching so that a
controller mapped to /person is also implicitly mapped to /person.*.
The file extension is then used to interpret the requested content type to use for
the response (that is, instead of the Accept header) — for example, /person.pdf,
/person.xml, and others.
Using file extensions in this way was necessary when browsers used to send Accept headers
that were hard to interpret consistently. At present, that is no longer a necessity and
using the Accept header should be the preferred choice.
Over time, the use of file name extensions has proven problematic in a variety of ways. It can cause ambiguity when overlain with the use of URI variables, path parameters, and URI encoding. Reasoning about URL-based authorization and security (see next section for more details) also become more difficult.
To completely disable the use of file extensions, you must set both of the following:
-
useSuffixPatternMatching(false), see PathMatchConfigurer -
favorPathExtension(false), see ContentNegotiationConfigurer
URL-based content negotiation can still be useful (for example, when typing a URL in a
browser). To enable that, we recommend a query parameter-based strategy to avoid most of
the issues that come with file extensions. Alternatively, if you must use file extensions, consider
restricting them to a list of explicitly registered extensions through the
mediaTypes property of ContentNegotiationConfigurer.
A reflected file download (RFD) attack is similar to XSS in that it relies on request input (for example, a query parameter and a 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 through URL path extensions.
Disabling suffix pattern matching and using 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. However, it can 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.
See CVE-2015-5211 for additional recommendations related to RFD.
You can narrow the request mapping based on the Content-Type of the request,
as the following example shows:
@PostMapping(path = "/pets", consumes = "application/json") (1)
public void addPet(@RequestBody Pet pet) {
// ...
}-
Using a
consumesattribute to narrow the mapping by the content type.
The consumes attribute also supports negation expressions — for example, !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
overrides rather than extends the class-level declaration.
|
Tip
|
MediaType provides constants for commonly used media types, such as
APPLICATION_JSON_VALUE and APPLICATION_XML_VALUE.
|
You can narrow the request mapping based on the Accept request header and the list of
content types that a controller method produces, as the following example shows:
@GetMapping(path = "/pets/{petId}", produces = "application/json;charset=UTF-8") (1)
@ResponseBody
public Pet getPet(@PathVariable String petId) {
// ...
}-
Using a
producesattribute to narrow the mapping by the content type.
The media type can specify a character set. Negated expressions are supported — for example,
!text/plain means any content type other than "text/plain".
|
Note
|
For the JSON content type, the UTF-8 charset should be specified even if RFC7159 clearly states that “no charset parameter is defined for this registration”, because some browsers require it to correctly interpret UTF-8 special characters. |
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
overrides rather than extends the class-level declaration.
|
Tip
|
MediaType provides constants for commonly used media types, such as
APPLICATION_JSON_UTF8_VALUE and APPLICATION_XML_VALUE.
|
You can narrow request mappings based on request parameter conditions. You can test for the
presence of a request parameter (myParam), for the absence of one (!myParam), or for a
specific value (myParam=myValue). The following example shows how to test for a specific value:
@GetMapping(path = "/pets/{petId}", params = "myParam=myValue") (1)
public void findPet(@PathVariable String petId) {
// ...
}-
Testing whether
myParamequalsmyValue.
You can also use the same with request header conditions, as the following example shows:
@GetMapping(path = "/pets", headers = "myHeader=myValue") (1)
public void findPet(@PathVariable String petId) {
// ...
}-
Testing whether
myHeaderequalsmyValue.
@GetMapping (and @RequestMapping(method=HttpMethod.GET)) support HTTP HEAD
transparently for request mapping. Controller methods do not 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 (without actually writing to the response).
@GetMapping (and @RequestMapping(method=HttpMethod.GET)) are implicitly mapped to
and support HTTP HEAD. An HTTP HEAD request is processed as if it were HTTP GET except
that, instead of writing the body, the number of bytes are counted and the Content-Length
header is set.
By default, HTTP OPTIONS is handled by setting the Allow response header to the list of HTTP
methods listed in all @RequestMapping methods that have 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, and others).
You can explicitly map the @RequestMapping method to HTTP HEAD and HTTP OPTIONS, but that
is not necessary in the common case.
Spring MVC supports the use of composed annotations
for request mapping. Those are annotations that are themselves meta-annotated with
@RequestMapping and composed to redeclare a subset (or all) of the @RequestMapping
attributes with a narrower, more specific purpose.
@GetMapping, @PostMapping, @PutMapping, @DeleteMapping, and @PatchMapping are
examples of composed annotations. They are provided because, arguably, most
controller methods should be mapped to a specific HTTP method versus using @RequestMapping,
which, by default, matches to all HTTP methods. If you need an example of composed
annotations, look at how those are declared.
Spring MVC also supports custom request-mapping attributes with custom request-matching
logic. This is a more advanced option that requires subclassing
RequestMappingHandlerMapping and overriding the getCustomMethodCondition method, where
you can check the custom attribute and return your own RequestCondition.
You can programmatically register handler methods, which you can use for dynamic registrations or for advanced cases, such as different instances of the same handler under different URLs. The following example registers a handler method:
@Configuration
public class MyConfig {
@Autowired
public void setHandlerMapping(RequestMappingHandlerMapping mapping, UserHandler handler) (1)
throws NoSuchMethodException {
RequestMappingInfo info = RequestMappingInfo
.paths("/user/{id}").methods(RequestMethod.GET).build(); (2)
Method method = UserHandler.class.getMethod("getUser", Long.class); (3)
mapping.registerMapping(info, handler, method); (4)
}
}-
Inject the target handler and the handler mapping for controllers.
-
Prepare the request mapping meta data.
-
Get the handler method.
-
Add the registration.
@RequestMapping handler methods have a flexible signature and can choose from a range of
supported controller method arguments and return values.
The next table describes the 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 (for example, @RequestParam, @RequestHeader,
and others) and is equivalent to required=false.
| Controller method argument | Description |
|---|---|
|
Generic access to request parameters and request and session attributes, without direct use of the Servlet API. |
|
Choose any specific request or response type — for example, |
|
Enforces the presence of a session. As a consequence, such an argument is never |
|
Servlet 4.0 push builder API for programmatic HTTP/2 resource pushes.
Note that, per the Servlet specification, the injected |
|
Currently authenticated user — possibly a specific |
|
The HTTP method of the request. |
|
The current request locale, determined by the most specific |
|
The time zone associated with the current request, as determined by a |
|
For access to the raw request body as exposed by the Servlet API. |
|
For access to the raw response body as exposed by the Servlet API. |
|
For access to URI template variables. See URI patterns. |
|
For access to name-value pairs in URI path segments. See Matrix Variables. |
|
For access to the Servlet request parameters, including multipart files. Parameter values
are converted to the declared method argument type. See Note that use of |
|
For access to request headers. Header values are converted to the declared method argument
type. See |
|
For access to cookies. Cookies values are converted to the declared method argument
type. See |
|
For access to the HTTP request body. Body content is converted to the declared method
argument type by using |
|
For access to request headers and body. The body is converted with an |
|
For access to a part in a |
|
For access to the model that is used in HTML controllers and exposed to templates as part of view rendering. |
|
Specify attributes to use in case of a redirect (that is, to be appended to the query string) and flash attributes to be stored temporarily until the request after redirect. See Redirect Attributes and Flash Attributes. |
|
For access to an existing attribute in the model (instantiated if not present) with
data binding and validation applied. See Note that use of |
|
For access to errors from validation and data binding for a command object
(that is, a |
|
For marking form processing complete, which triggers cleanup of session attributes
declared through a class-level |
|
For preparing a URL relative to the current request’s host, port, scheme, context path, and the literal part of the servlet mapping. See URI Links. |
|
For access to any session attribute, in contrast to model attributes stored in the session
as a result of a class-level |
|
For access to request attributes. See |
Any other argument |
If a method argument is not matched to any of the earlier values in this table and it is
a simple type (as determined by
{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty],
it is a resolved as a |
The next table describes the supported controller method return values. Reactive types are supported for all return values.
| Controller method return value | Description |
|---|---|
|
The return value is converted through |
|
The return value that specifies the full response (including HTTP headers and body) is to be converted
through |
|
For returning a response with headers and no body. |
|
A view name to be resolved with |
|
A |
|
Attributes to be added to the implicit model, with the view name implicitly determined
through a |
|
An attribute to be added to the model, with the view name implicitly determined through
a Note that |
|
The view and model attributes to use and, optionally, a response status. |
|
A method with a If none of the above is true, a |
|
Produce any of the preceding return values asynchronously from any thread — for example, as a
result of some event or callback. See Asynchronous Requests and
|
|
Produce any of the above return values asynchronously in a Spring MVC-managed thread.
See Asynchronous Requests and |
|
Alternative to |
|
Emit a stream of objects asynchronously to be written to the response with
|
|
Write to the response |
Reactive types — Reactor, RxJava, or others through |
Alternative to For streaming scenarios (for example, See Asynchronous Requests and Reactive Types. |
Any other return value |
Any return value that does not match any of the earlier values in this table and that
is a |
Some annotated controller method arguments that represent String-based request input (such as
@RequestParam, @RequestHeader, @PathVariable, @MatrixVariable, and @CookieValue)
can require type conversion if the argument is declared as something other than String.
For such cases, type conversion is automatically applied based on the configured converters.
By default, simple types (int, long, Date, and others) are supported. You can customize type conversion
through a WebDataBinder (see DataBinder) or by registering
Formatters with the FormattingConversionService. See
Spring Field Formatting.
RFC 3986 discusses name-value pairs in path segments. In Spring MVC, we refer to those as “matrix variables” based on an “old post” by Tim Berners-Lee, but they can be also be referred to as URI path parameters.
Matrix variables can appear in any path segment, with each variable separated by a semicolon and
multiple values separated by comma (for example, /cars;color=red,green;year=2012). Multiple
values can also be specified through repeated variable names (for example,
color=red;color=green;color=blue).
If a URL is expected to contain matrix variables, the request mapping for a controller method must use a URI variable to mask that variable content and ensure the request can be matched successfully independent of matrix variable order and presence. The following example uses a matrix variable:
// GET /pets/42;q=11;r=22
@GetMapping("/pets/{petId}")
public void findPet(@PathVariable String petId, @MatrixVariable int q) {
// petId == 42
// q == 11
}Given that all path segments may contain matrix variables, you may sometimes need to disambiguate which path variable the matrix variable is expected to be in. The following example shows how to do so:
// 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, as the following example shows:
// GET /pets/42
@GetMapping("/pets/{petId}")
public void findPet(@MatrixVariable(required=false, defaultValue="1") int q) {
// q == 1
}To get all matrix variables, you can use a MultiValueMap, as the following example shows:
// GET /owners/42;q=11;r=12/pets/21;q=22;s=23
@GetMapping("/owners/{ownerId}/pets/{petId}")
public void findPet(
@MatrixVariable MultiValueMap<String, String> matrixVars,
@MatrixVariable(pathVar="petId") MultiValueMap<String, String> petMatrixVars) {
// matrixVars: ["q" : [11,22], "r" : 12, "s" : 23]
// petMatrixVars: ["q" : 22, "s" : 23]
}Note that you need to enable the use of matrix variables. In the MVC Java configuration,
you need to set a UrlPathHelper with removeSemicolonContent=false through
Path Matching. In the MVC XML namespace, you can set
<mvc:annotation-driven enable-matrix-variables="true"/>.
You can use the @RequestParam annotation to bind Servlet request parameters (that is,
query parameters or form data) to a method argument in a controller.
The following example shows how to do so:
@Controller
@RequestMapping("/pets")
public class EditPetForm {
// ...
@GetMapping
public String setupForm(@RequestParam("petId") int petId, Model model) { (1)
Pet pet = this.clinic.loadPet(petId);
model.addAttribute("pet", pet);
return "petForm";
}
// ...
}-
Using
@RequestParamto bindpetId.
By default, method parameters that use this annotation are required, but you can specify that
a method parameter is optional by setting the @RequestParam annotation’s required flag to
false or by declaring the argument with an java.util.Optional wrapper.
Type conversion is automatically applied if the target method parameter type is not
String. See Type Conversion.
Declaring the argument type as an array or list allows for resolving multiple parameter values for the same parameter name.
When an @RequestParam annotation is declared as a Map<String, String> or
MultiValueMap<String, String>, without a parameter name specified in the annotation,
then the map is populated with the request parameter values for each given parameter name.
Note that use of @RequestParam is optional (for example, to set its attributes).
By default, any argument that is a simple value type (as determined by
{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty])
and is not resolved by any other argument resolver, is treated as if it were annotated
with @RequestParam.
You can use the @RequestHeader annotation to bind a request header to a method argument in a
controller.
Consider the following request, with headers:
Host localhost:8080 Accept text/html,application/xhtml+xml,application/xml;q=0.9 Accept-Language fr,en-gb;q=0.7,en;q=0.3 Accept-Encoding gzip,deflate Accept-Charset ISO-8859-1,utf-8;q=0.7,*;q=0.7 Keep-Alive 300
The following example gets the value of the Accept-Encoding and Keep-Alive headers:
@GetMapping("/demo")
public void handle(
@RequestHeader("Accept-Encoding") String encoding, (1)
@RequestHeader("Keep-Alive") long keepAlive) { (2)
//...
}-
Get the value of the
Accept-Encodingheader. -
Get the value of the
Keep-Aliveheader.
If the target method parameter type is not
String, type conversion is automatically applied. 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 or collection of strings or other types known to the type conversion system. For
example, a method parameter annotated with @RequestHeader("Accept") can be of type
String but also String[] or List<String>.
|
You can use the @CookieValue annotation to bind the value of an HTTP cookie to a method argument
in a controller.
Consider a request with the following cookie:
JSESSIONID=415A4AC178C59DACE0B2C9CA727CDD84
The following example shows how to get the cookie value:
@GetMapping("/demo")
public void handle(@CookieValue("JSESSIONID") String cookie) { (1)
//...
}-
Get the value of the
JSESSIONIDcookie.
if the target method parameter type is not
String, type conversion is applied automatically. See Type Conversion.
You can use the @ModelAttribute annotation on a method argument to access an attribute from the
model or have it be instantiated if not present. The model attribute is also overlain with
values from HTTP Servlet request parameters whose names match to field names. This is
referred to as data binding, and it saves you from having to deal with parsing and
converting individual query parameters and form fields. The following example shows how to do so:
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute Pet pet) { } (1)-
Bind an instance of
Pet.
The Pet instance above is resolved as follows:
-
From the model if already added by using Model.
-
From the HTTP session by using
@SessionAttributes. -
From a URI path variable passed through a
Converter(see the next example). -
From the invocation of a default constructor.
-
From the invocation of a “primary constructor” with arguments that match to Servlet request parameters. Argument names are determined through JavaBeans
@ConstructorPropertiesor through runtime-retained parameter names in the bytecode.
While it is common to use a Model to populate the model with
attributes, one other alternative is to rely on a Converter<String, T> in combination
with a URI path variable convention. In the following example, the model attribute name,
account, matches the URI path variable, account, and the Account is loaded by passing
the String account number through a registered Converter<String, Account>:
@PutMapping("/accounts/{account}")
public String save(@ModelAttribute("account") Account account) {
// ...
}After the model attribute instance is obtained, data binding is applied. The
WebDataBinder class matches Servlet request parameter names (query parameters and form
fields) to field names on the target Object. Matching fields are populated after type
conversion is applied, where necessary. For more on data binding (and validation), see
Validation. For more on customizing data binding, see
DataBinder.
Data binding can result in errors. By default, a BindException is raised. However, to check
for such errors in the controller method, you can add a BindingResult argument immediately next
to the @ModelAttribute, as the following example shows:
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@ModelAttribute("pet") Pet pet, BindingResult result) { (1)
if (result.hasErrors()) {
return "petForm";
}
// ...
}-
Adding a
BindingResultnext to the@ModelAttribute.
In some cases, you may want access to a model attribute without data binding. For such
cases, you can inject the Model into the controller and access it directly or,
alternatively, set @ModelAttribute(binding=false), as the following example shows:
@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) { (1)
// ...
}-
Setting
@ModelAttribute(binding=false).
You can automatically apply validation after data binding by adding the
javax.validation.Valid annotation or Spring’s @Validated annotation (ee
Bean validation and
Spring validation). The following example shows how to do so:
@PostMapping("/owners/{ownerId}/pets/{petId}/edit")
public String processSubmit(@Valid @ModelAttribute("pet") Pet pet, BindingResult result) { (1)
if (result.hasErrors()) {
return "petForm";
}
// ...
}-
Validate the
Petinstance.
Note that using @ModelAttribute is optional (for example, to set its attributes).
By default, any argument that is not a simple value type (as determined by
{api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty])
and is not resolved by any other argument resolver is treated as if it were annotated
with @ModelAttribute.
@SessionAttributes is used to store model attributes in the HTTP Servlet session between
requests. It is a type-level annotation that declares the session attributes used by a
specific controller. This typically lists the names of model attributes or types of
model attributes that should be transparently stored in the session for subsequent
requests to access.
The following example uses the @SessionAttributes annotation:
@Controller
@SessionAttributes("pet") (1)
public class EditPetForm {
// ...
}-
Using the
@SessionAttributesannotation.
On the first request, when a model attribute with the name, pet, is added to the model,
it is automatically promoted to and saved in the HTTP Servlet session. It remains there
until another controller method uses a SessionStatus method argument to clear the
storage, as the following example shows:
@Controller
@SessionAttributes("pet") (1)
public class EditPetForm {
// ...
@PostMapping("/pets/{id}")
public String handle(Pet pet, BindingResult errors, SessionStatus status) {
if (errors.hasErrors) {
// ...
}
status.setComplete(); (2)
// ...
}
}
}-
Storing the
Petvalue in the Servlet session. -
Clearing the
Petvalue from the Servlet session.
If you need access to pre-existing session attributes that are managed globally
(that is, outside the controller — for example, by a filter) and may or may not be present,
you can use the @SessionAttribute annotation on a method parameter,
as the following example shows:
@RequestMapping("/")
public String handle(@SessionAttribute User user) { (1)
// ...
}-
Using a
@SessionAttributeannotation.
For use cases that require adding or removing session attributes, consider injecting
org.springframework.web.context.request.WebRequest or
javax.servlet.http.HttpSession into the controller method.
For temporary storage of model attributes in the session as part of a controller
workflow, consider using @SessionAttributes as described in
@SessionAttributes.
Similar to @SessionAttribute, you can use the @RequestAttribute annotations to
access pre-existing request attributes created earlier (for example, by a Servlet Filter
or HandlerInterceptor):
@GetMapping("/")
public String handle(@RequestAttribute Client client) { (1)
// ...
}-
Using the
@RequestAttributeannotation.
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 or arrays of primitive types are automatically appended as query parameters.
Appending primitive type attributes as query parameters can be the desired result if a
model instance was prepared specifically for the redirect. However, in annotated
controllers, the model can contain additional attributes added for rendering purposes (for example,
drop-down field values). To avoid the possibility of having such attributes appear in the
URL, a @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, which you can use to indicate that 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 does not do so,
no attributes should be passed on to RedirectView. Both the MVC namespace and the MVC
Java configuration keep this flag set to false, 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 you need explicitly add them
through Model or RedirectAttributes. The following example shows how to define a redirect:
@PostMapping("/files/{path}")
public String upload(...) {
// ...
return "redirect:files/{path}";
}Another way of passing data to the redirect target is by using flash attributes. Unlike other redirect attributes, flash attributes are saved in the HTTP session (and, hence, do not appear in the URL). See Flash Attributes for more information.
Flash attributes provide a way for one request to store attributes that are 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 are 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. However,
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, a
@RequestMapping method can accept an argument of type RedirectAttributes and use it
to add flash attributes for a redirect scenario. Flash attributes added through
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 that serves the target URL.
The concept of flash attributes exists in many other web frameworks and has proven to sometimes be exposed 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 (for example, 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
it looks up the “input” FlashMap.
This does not entirely eliminate the possibility of a concurrency issue but reduces it greatly with information that is already available in the redirect URL. Therefore, we recommend that you use flash attributes mainly for redirect scenarios.
After a MultipartResolver has been enabled, the content of POST
requests with multipart/form-data is parsed and accessible as regular request
parameters. The following example accesses one regular form field and one uploaded
file:
@Controller
public class FileUploadController {
@PostMapping("/form")
public String handleFormUpload(@RequestParam("name") String name,
@RequestParam("file") MultipartFile file) {
if (!file.isEmpty()) {
byte[] bytes = file.getBytes();
// store the bytes somewhere
return "redirect:uploadSuccess";
}
return "redirect:uploadFailure";
}
}Declaring the argument type as a List<MultipartFile> allows for resolving multiple
files for the same parameter name.
When the @RequestParam annotation is declared as a Map<String, MultipartFile> or
MultiValueMap<String, MultipartFile>, without a parameter name specified in the annotation,
then the map is populated with the multipart files for each given parameter name.
|
Note
|
With Servlet 3.0 multipart parsing, you may also declare javax.servlet.http.Part
instead of Spring’s MultipartFile, as a method argument or collection value type.
|
You can also use multipart content as part of data binding to a command object. For example, the form field and file from the preceding example could be fields on a form object, as the following example shows:
class MyForm {
private String name;
private MultipartFile file;
// ...
}
@Controller
public class FileUploadController {
@PostMapping("/form")
public String handleFormUpload(MyForm form, BindingResult errors) {
if (!form.getFile().isEmpty()) {
byte[] bytes = form.getFile().getBytes();
// store the bytes somewhere
return "redirect:uploadSuccess";
}
return "redirect:uploadFailure";
}
}Multipart requests can also be submitted from non-browser clients in a RESTful service scenario. The following example shows a file with JSON:
POST /someUrl
Content-Type: multipart/mixed
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="meta-data"
Content-Type: application/json; charset=UTF-8
Content-Transfer-Encoding: 8bit
{
"name": "value"
}
--edt7Tfrdusa7r3lNQc79vXuhIIMlatb7PQg7Vp
Content-Disposition: form-data; name="file-data"; filename="file.properties"
Content-Type: text/xml
Content-Transfer-Encoding: 8bit
... File Data ...
You can access the "meta-data" part with @RequestParam as a String but you’ll
probably want it deserialized from JSON (similar to @RequestBody). Use the
@RequestPart annotation to access a multipart after converting it with an
HttpMessageConverter:
@PostMapping("/")
public String handle(@RequestPart("meta-data") MetaData metadata,
@RequestPart("file-data") MultipartFile file) {
// ...
}You can use @RequestPart in combination with javax.validation.Valid or use Spring’s
@Validated annotation, both of which cause Standard Bean Validation to be applied.
By default, validation errors cause a MethodArgumentNotValidException, which is turned
into a 400 (BAD_REQUEST) response. Alternatively, you can handle validation errors locally
within the controller through an Errors or BindingResult argument,
as the following example shows:
@PostMapping("/")
public String handle(@Valid @RequestPart("meta-data") MetaData metadata,
BindingResult result) {
// ...
}You can use the @RequestBody annotation to have the request body read and deserialized into an
Object through an HttpMessageConverter.
The following example uses a @RequestBody argument:
@PostMapping("/accounts")
public void handle(@RequestBody Account account) {
// ...
}You can use the Message Converters option of the MVC Config to configure or customize message conversion.
You can use @RequestBody in combination with javax.validation.Valid or Spring’s
@Validated annotation, both of which cause Standard Bean Validation to be applied.
By default, validation errors cause a MethodArgumentNotValidException, which is turned
into a 400 (BAD_REQUEST) response. Alternatively, you can handle validation errors locally
within the controller through an Errors or BindingResult argument,
as the following example shows:
@PostMapping("/accounts")
public void handle(@Valid @RequestBody Account account, BindingResult result) {
// ...
}HttpEntity is more or less identical to using @RequestBody but is based on a
container object that exposes request headers and body. The following listing shows an example:
@PostMapping("/accounts")
public void handle(HttpEntity<Account> entity) {
// ...
}You can use the @ResponseBody annotation on a method to have the return serialized to the
response body through an
HttpMessageConverter. The following listing shows an example:
@GetMapping("/accounts/{id}")
@ResponseBody
public Account handle() {
// ...
}@ResponseBody is also supported at the class level, in which case it is inherited by
all controller methods. This is the effect of @RestController, which is nothing more
than a meta-annotation marked with @Controller and @ResponseBody.
You can use @ResponseBody with reactive types.
See Asynchronous Requests and Reactive Types for more details.
You can use the Message Converters option of the MVC Config to configure or customize message conversion.
You can combine @ResponseBody methods with JSON serialization views.
See Jackson JSON for details.
ResponseEntity is like @ResponseBody but with status and headers. For example:
@GetMapping("/something")
public ResponseEntity<String> handle() {
String body = ... ;
String etag = ... ;
return ResponseEntity.ok().eTag(etag).build(body);
}Spring MVC supports using a single value reactive type
to produce the ResponseEntity asynchronously, and/or single and multi-value reactive
types for the body.
Spring offers support for the Jackson JSON library.
Spring MVC provides built-in support for
Jackson’s Serialization Views,
which allow rendering only a subset of all fields in an Object. To use it with
@ResponseBody or ResponseEntity controller methods, you can use Jackson’s
@JsonView annotation to activate a serialization view class, as the following example shows:
@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
|
@JsonView allows an array of view classes, but you can specify only one per
controller method. If you need to activate multiple views, you can use a composite interface.
|
For controllers that rely on view resolution, you can add the serialization view class to the model, as the following example shows:
@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";
}
}You can use the @ModelAttribute annotation:
-
On a method argument in
@RequestMappingmethods to create or access anObjectfrom the model and to bind it to the request through aWebDataBinder. -
As a method-level annotation in
@Controlleror@ControllerAdviceclasses that help to initialize the model prior to any@RequestMappingmethod invocation. -
On a
@RequestMappingmethod to mark its return value is a model attribute.
This section discusses @ModelAttribute methods — the second item in the preceding list.
A controller can have any number of @ModelAttribute methods. All such methods are
invoked before @RequestMapping methods in the same controller. A @ModelAttribute
method can also be shared across controllers through @ControllerAdvice. See the section on
Controller Advice for more details.
@ModelAttribute methods have flexible method signatures. They support many of the same
arguments as @RequestMapping methods, except for @ModelAttribute itself or anything
related to the request body.
The following example shows a @ModelAttribute method:
@ModelAttribute
public void populateModel(@RequestParam String number, Model model) {
model.addAttribute(accountRepository.findAccount(number));
// add more ...
}The following example adds only one attribute:
@ModelAttribute
public Account addAccount(@RequestParam String number) {
return accountRepository.findAccount(number);
}|
Note
|
When a name is not explicitly specified, a default name is chosen based on the Object
type, as explained in the javadoc for {api-spring-framework}/core/Conventions.html[Conventions].
You can always assign an explicit name by using the overloaded addAttribute method or
through the name attribute on @ModelAttribute (for a return value).
|
You can also use @ModelAttribute as a method-level annotation on @RequestMapping methods,
in which case the return value of the @RequestMapping method is interpreted as a model
attribute. This is typically not required, as it is the default behavior in HTML controllers,
unless the return value is a String that would otherwise be interpreted as a view name.
@ModelAttribute can also customize the model attribute name, as the following example shows:
@GetMapping("/accounts/{id}")
@ModelAttribute("myAccount")
public Account handle() {
// ...
return account;
}@Controller or @ControllerAdvice classes can have @InitBinder methods that
initialize instances of WebDataBinder, and those, in turn, can:
-
Bind request parameters (that is, form or query data) to a model object.
-
Convert String-based request values (such as request parameters, path variables, headers, cookies, and others) to the target type of controller method arguments.
-
Format model object values as
Stringvalues when rendering HTML forms.
@InitBinder methods can register controller-specific java.bean.PropertyEditor or
Spring Converter and Formatter components. In addition, you can use the
MVC config to register Converter and Formatter
types in a globally shared FormattingConversionService.
@InitBinder methods support many of the same arguments that @RequestMapping methods
do, except for @ModelAttribute (command object) arguments. Typically, they are declared
with a WebDataBinder argument (for registrations) and a void return value.
The following listing shows an example:
@Controller
public class FormController {
@InitBinder (1)
public void initBinder(WebDataBinder binder) {
SimpleDateFormat dateFormat = new SimpleDateFormat("yyyy-MM-dd");
dateFormat.setLenient(false);
binder.registerCustomEditor(Date.class, new CustomDateEditor(dateFormat, false));
}
// ...
}-
Defining an
@InitBindermethod.
Alternatively, when you use a Formatter-based setup through a shared
FormattingConversionService, you can re-use the same approach and register
controller-specific Formatter implementations, as the following example shows:
@Controller
public class FormController {
@InitBinder (1)
protected void initBinder(WebDataBinder binder) {
binder.addCustomFormatter(new DateFormatter("yyyy-MM-dd"));
}
// ...
}-
Defining an
@InitBindermethod on a custom formatter.
@Controller and @ControllerAdvice classes can have
@ExceptionHandler methods to handle exceptions from controller methods, as the following example shows:
@Controller
public class SimpleController {
// ...
@ExceptionHandler
public ResponseEntity<String> handle(IOException ex) {
// ...
}
}The exception may match against a top-level exception being propagated (that is, a direct
IOException being thrown) or against the immediate cause within a top-level wrapper exception
(for example, an IOException wrapped inside an IllegalStateException).
For matching exception types, preferably declare the target exception as a method argument,
as the preceding example shows. When multiple exception methods match, a root exception match is generally
preferred to a cause exception match. More specifically, the ExceptionDepthComparator is
used to sort exceptions based on their depth from the thrown exception type.
Alternatively, the annotation declaration may narrow the exception types to match, as the following example shows:
@ExceptionHandler({FileSystemException.class, RemoteException.class})
public ResponseEntity<String> handle(IOException ex) {
// ...
}You can even use a list of specific exception types with a very generic argument signature, as the following example shows:
@ExceptionHandler({FileSystemException.class, RemoteException.class})
public ResponseEntity<String> handle(Exception ex) {
// ...
}|
Note
|
The distinction between root and cause exception matching can be surprising. In the The behavior is even simpler in the |
We generally recommend that you be as specific as possible in the argument signature,
reducing the potential for mismatches between root and cause exception types.
Consider breaking a multi-matching method into individual @ExceptionHandler
methods, each matching a single specific exception type through its signature.
In a multi-@ControllerAdvice arrangement, we recommend declaring your primary root exception
mappings on a @ControllerAdvice prioritized with a corresponding order. While a root
exception match is preferred to a cause, this is defined among the methods of a given
controller or @ControllerAdvice class. This means a cause match on a higher-priority
@ControllerAdvice bean is preferred to any match (for example, root) on a lower-priority
@ControllerAdvice bean.
Last but not least, an @ExceptionHandler method implementation can choose to back
out of dealing with a given exception instance by rethrowing it in its original form.
This is useful in scenarios where you are interested only in root-level matches or in
matches within a specific context that cannot be statically determined. A rethrown
exception is propagated through the remaining resolution chain, as though
the given @ExceptionHandler method would not have matched in the first place.
Support for @ExceptionHandler methods in Spring MVC is built on the DispatcherServlet
level, HandlerExceptionResolver mechanism.
@ExceptionHandler methods support the following arguments:
| Method argument | Description |
|---|---|
Exception type |
For access to the raised exception. |
|
For access to the controller method that raised the exception. |
|
Generic access to request parameters and request and session attributes without direct use of the Servlet API. |
|
Choose any specific request or response type (for example, |
|
Enforces the presence of a session. As a consequence, such an argument is never |
|
Currently authenticated user — possibly a specific |
|
The HTTP method of the request. |
|
The current request locale, determined by the most specific |
|
The time zone associated with the current request, as determined by a |
|
For access to the raw response body, as exposed by the Servlet API. |
|
For access to the model for an error response. Always empty. |
|
Specify attributes to use in case of a redirect — (that is to be appended to the query string) and flash attributes to be stored temporarily until the request after the redirect. See Redirect Attributes and Flash Attributes. |
|
For access to any session attribute, in contrast to model attributes stored in the session
as a result of a class-level |
|
For access to request attributes. See |
@ExceptionHandler methods support the following return values:
| Return value | Description |
|---|---|
|
The return value is converted through |
|
The return value specifies that the full response (including the HTTP headers and the body) be converted
through |
|
A view name to be resolved with |
|
A |
|
Attributes to be added to the implicit model with the view name implicitly determined
through a |
|
An attribute to be added to the model with the view name implicitly determined through
a Note that |
|
The view and model attributes to use and, optionally, a response status. |
|
A method with a If none of the above is true, a |
Any other return value |
If a return value is not matched to any of the above and is not a simple type (as determined by {api-spring-framework}/beans/BeanUtils.html#isSimpleProperty-java.lang.Class-[BeanUtils#isSimpleProperty]), by default, it is treated as a model attribute to be added to the model. If it is a simple type, it remains unresolved. |
A common requirement for REST services is to include error details in the body of the
response. The Spring Framework does not automatically do this because the representation
of error details in the response body is application-specific. However, a
@RestController may use @ExceptionHandler methods with a ResponseEntity return
value to set the status and the body of the response. Such methods can also be declared
in @ControllerAdvice classes to apply them globally.
Applications that implement global exception handling with error details in the response
body should consider extending
{api-spring-framework}/web/servlet/mvc/method/annotation/ResponseEntityExceptionHandler.html[ResponseEntityExceptionHandler],
which provides handling for exceptions that Spring MVC raises and provides hooks to
customize the response body. To make use of this, create a subclass of
ResponseEntityExceptionHandler, annotate it with @ControllerAdvice, override the
necessary methods, and declare it as a Spring bean.
Typically @ExceptionHandler, @InitBinder, and @ModelAttribute methods apply within
the @Controller class (or class hierarchy) in which they are declared. If you want such
methods to apply more globally (across controllers), you can declare them in a class
marked with @ControllerAdvice or @RestControllerAdvice.
@ControllerAdvice is marked with @Component, which means such classes can be registered
as Spring beans through component scanning.
@RestControllerAdvice is also a meta-annotation marked with both @ControllerAdvice and
@ResponseBody, which essentially means @ExceptionHandler methods are rendered to the
response body through message conversion (versus view resolution or template rendering).
On startup, the infrastructure classes for @RequestMapping and @ExceptionHandler methods
detect Spring beans of type @ControllerAdvice and then apply their methods at runtime.
Global @ExceptionHandler methods (from an @ControllerAdvice) are applied after local
ones (from the @Controller). By contrast, global @ModelAttribute and @InitBinder
methods are applied before local ones.
By default, @ControllerAdvice methods apply to every request (that is, all controllers), but
you can narrow that down to a subset of controllers by using attributes on the annotation,
as the following example shows:
// Target all Controllers annotated with @RestController
@ControllerAdvice(annotations = RestController.class)
public class ExampleAdvice1 {}
// Target all Controllers within specific packages
@ControllerAdvice("org.example.controllers")
public class ExampleAdvice2 {}
// Target all Controllers assignable to specific classes
@ControllerAdvice(assignableTypes = {ControllerInterface.class, AbstractController.class})
public class ExampleAdvice3 {}The selectors in the preceding example are evaluated at runtime and may negatively impact
performance if used extensively. See the
{api-spring-framework}/web/bind/annotation/ControllerAdvice.html[@ControllerAdvice]
javadoc for more details.
This section describes various options available in the Spring Framework to work with URI’s.
You can use ServletUriComponentsBuilder to create URIs relative to the current request,
as the following example shows:
HttpServletRequest request = ...
// Re-uses host, scheme, port, path and query string...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromRequest(request)
.replaceQueryParam("accountId", "{id}").build()
.expand("123")
.encode();You can create URIs relative to the context path, as the following example shows:
// Re-uses host, port and context path...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromContextPath(request)
.path("/accounts").build()You can create URIs relative to a Servlet (for example, /main/*),
as the following example shows:
// Re-uses host, port, context path, and Servlet prefix...
ServletUriComponentsBuilder ucb = ServletUriComponentsBuilder.fromServletMapping(request)
.path("/accounts").build()|
Note
|
As of 5.1, ServletUriComponentsBuilder ignores information from the Forwarded and
X-Forwarded-* headers, which specify the client-originated address. Consider using the
ForwardedHeaderFilter to extract and use or to discard
such headers.
|
Spring MVC provides a mechanism to prepare links to controller methods. For example, the following MVC controller allows for link creation:
@Controller
@RequestMapping("/hotels/{hotel}")
public class BookingController {
@GetMapping("/bookings/{booking}")
public ModelAndView getBooking(@PathVariable Long booking) {
// ...
}
}You can prepare a link by referring to the method by name, as the following example shows:
UriComponents uriComponents = MvcUriComponentsBuilder
.fromMethodName(BookingController.class, "getBooking", 21).buildAndExpand(42);
URI uri = uriComponents.encode().toUri();In the preceding example, we provide 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 provide the
value, 42, 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, we could 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, as the following example shows
(the example assumes static import of MvcUriComponentsBuilder.on):
UriComponents uriComponents = MvcUriComponentsBuilder
.fromMethodCall(on(BookingController.class).getBooking(21)).buildAndExpand(42);
URI uri = uriComponents.encode().toUri();|
Note
|
Controller method signatures are limited in their design when they are supposed to be usable for
link creation with fromMethodCall. Aside from needing a proper parameter signature,
there is a technical limitation on the return type (namely, generating a runtime proxy
for link builder invocations), so the return type must not be final. In particular,
the common String return type for view names does not work here. You should use ModelAndView
or even plain Object (with a String return value) instead.
|
The earlier 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 can be insufficient. For example, you may be outside the context of
a request (such as a batch process that prepares links) or perhaps you need to insert a path
prefix (such as 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 a base URL. Alternatively, you can create an instance of MvcUriComponentsBuilder
with a base URL and then use the instance-based withXxx methods. For example, the
following listing uses withMethodCall:
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();|
Note
|
As of 5.1, MvcUriComponentsBuilder ignores information from the Forwarded and
X-Forwarded-* headers, which specify the client-originated address. Consider using the
ForwardedHeaderFilter to extract and use or to discard
such headers.
|
In views such as Thymeleaf, FreeMarker, or JSP, you can build links to annotated controllers by referring to the implicitly or explicitly assigned name for each request mapping.
Consider the following example:
@RequestMapping("/people/{id}/addresses")
public class PersonAddressController {
@RequestMapping("/{country}")
public HttpEntity getAddress(@PathVariable String country) { ... }
}Given the preceding controller, 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 preceding example relies on the mvcUrl function declared in the Spring tag library
(that is, META-INF/spring.tld), but it is easy to define your own function or prepare a
similar one for other templating technologies.
Here is how this works. On startup, every @RequestMapping is assigned a default name
through HandlerMethodMappingNamingStrategy, whose default implementation uses the
capital letters of the class and the method name (for example, the getThing method in
ThingController becomes "TC#getThing"). If there is a name clash, you can use
@RequestMapping(name="..") to assign an explicit name or implement your own
HandlerMethodMappingNamingStrategy.
Spring MVC has an extensive integration with Servlet 3.0 asynchronous request processing:
-
DeferredResultandCallablereturn values in controller methods and provide basic support for a single asynchronous return value. -
Controllers can stream multiple values, including SSE and raw data.
-
Controllers can use reactive clients and return reactive types for response handling.
Once the asynchronous request processing feature is
enabled in the Servlet container, controller methods can
wrap any supported controller method return value with DeferredResult, as the following
example shows:
@GetMapping("/quotes")
@ResponseBody
public DeferredResult<String> quotes() {
DeferredResult<String> deferredResult = new DeferredResult<String>();
// Save the deferredResult somewhere..
return deferredResult;
}
// From some other thread...
deferredResult.setResult(data);The controller can produce the return value asynchronously, from a different thread — for example, in response to an external event (JMS message), a scheduled task, or other event.
A controller can wrap any supported return value with java.util.concurrent.Callable,
as the following example shows:
@PostMapping
public Callable<String> processUpload(final MultipartFile file) {
return new Callable<String>() {
public String call() throws Exception {
// ...
return "someView";
}
};
}The return value can then be obtained by running the the given task through the
configured TaskExecutor.
Here is a very concise overview of Servlet asynchronous request processing:
-
A
ServletRequestcan be put in asynchronous mode by callingrequest.startAsync(). The main effect of doing so is that the Servlet (as well as any filters) can exit, but the response remains open to let processing complete later. -
The call to
request.startAsync()returnsAsyncContext, which you can use for further control over asynchronous processing. For example, it provides thedispatchmethod, which is similar to a forward from the Servlet API, except that it lets an application resume request processing on a Servlet container thread. -
The
ServletRequestprovides access to the currentDispatcherType, which you can use to distinguish between processing the initial request, an asynchronous dispatch, a forward, and other dispatcher types.
DeferredResult processing works as follows:
-
The controller returns a
DeferredResultand saves it in some in-memory queue or list where it can be accessed. -
Spring MVC calls
request.startAsync(). -
Meanwhile, the
DispatcherServletand all configured filters exit the request processing thread, but the response remains open. -
The application sets the
DeferredResultfrom some thread, and Spring MVC dispatches the request back to the Servlet container. -
The
DispatcherServletis invoked again, and processing resumes with the asynchronously produced return value.
Callable processing works as follows:
-
The controller returns a
Callable. -
Spring MVC calls
request.startAsync()and submits theCallableto aTaskExecutorfor processing in a separate thread. -
Meanwhile, the
DispatcherServletand all filters exit the Servlet container thread, but the response remains open. -
Eventually the
Callableproduces a result, and Spring MVC dispatches the request back to the Servlet container to complete processing. -
The
DispatcherServletis invoked again, and processing resumes with the asynchronously produced return value from theCallable.
For further background and context, you can also read the blog posts that introduced asynchronous request processing support in Spring MVC 3.2.
When you use a DeferredResult, you can choose whether to call setResult or
setErrorResult with an exception. In both cases, Spring MVC dispatches the request back
to the Servlet container to complete processing. It is then treated either as if the
controller method returned the given value or as if it produced the given exception.
The exception then goes through the regular exception handling mechanism (for example, invoking
@ExceptionHandler methods).
When you use Callable, similar processing logic occurs, the main difference being that
the result is returned from the Callable or an exception is raised by it.
HandlerInterceptor instances can be of type AsyncHandlerInterceptor, to receive the
afterConcurrentHandlingStarted callback on the initial request that starts asynchronous
processing (instead of postHandle and afterCompletion).
HandlerInterceptor implementations can also register a CallableProcessingInterceptor
or a DeferredResultProcessingInterceptor, to integrate more deeply with the
lifecycle of an asynchronous request (for example, to handle a timeout event). See
{api-spring-framework}/web/servlet/AsyncHandlerInterceptor.html[AsyncHandlerInterceptor]
for more details.
DeferredResult provides onTimeout(Runnable) and onCompletion(Runnable) callbacks.
See the {api-spring-framework}/web/context/request/async/DeferredResult.html[javadoc of DeferredResult]
for more details. Callable can be substituted for WebAsyncTask that exposes additional
methods for timeout and completion callbacks.
The Servlet API was originally built for making a single pass through the Filter-Servlet
chain. Asynchronous request processing, added in Servlet 3.0, lets applications exit
the Filter-Servlet chain but leave the response open for further processing. The Spring MVC
asynchronous support is built around that mechanism. When a controller returns a DeferredResult,
the Filter-Servlet chain is exited, and the Servlet container thread is released. Later, when
the DeferredResult is set, an ASYNC dispatch (to the same URL) is made, during which the
controller is mapped again but, rather than invoking it, the DeferredResult value is used
(as if the controller returned it) to resume processing.
By contrast, Spring WebFlux is neither built on the Servlet API, nor does it need such an asynchronous request processing feature, because it is asynchronous by design. Asynchronous handling is built into all framework contracts and is intrinsically supported through all stages of request processing.
From a programming model perspective, both Spring MVC and Spring WebFlux support asynchronous and Reactive Types as return values in controller methods. Spring MVC even supports streaming, including reactive back pressure. However, individual writes to the response remain blocking (and are performed on a separate thread), unlike WebFlux, which relies on non-blocking I/O and does not need an extra thread for each write.
Another fundamental difference is that Spring MVC does not support asynchronous or reactive
types in controller method arguments (for example, @RequestBody, @RequestPart, and others),
nor does it have any explicit support for asynchronous and reactive types as model attributes.
Spring WebFlux does support all that.
You can use DeferredResult and Callable for a single asynchronous return value.
What if you want to produce multiple asynchronous values and have those written to the
response? This section describes how to do so.
You can use the ResponseBodyEmitter return value to produce a stream of objects, where
each object is serialized with an
HttpMessageConverter and written to the
response, as the following example shows:
@GetMapping("/events")
public ResponseBodyEmitter handle() {
ResponseBodyEmitter emitter = new ResponseBodyEmitter();
// Save the emitter somewhere..
return emitter;
}
// In some other thread
emitter.send("Hello once");
// and again later on
emitter.send("Hello again");
// and done at some point
emitter.complete();You can also use ResponseBodyEmitter as the body in a ResponseEntity, letting you
customize the status and headers of the response.
When an emitter throws an IOException (for example, if the remote client went away), applications
are not responsible for cleaning up the connection and should not invoke emitter.complete
or emitter.completeWithError. Instead, the servlet container automatically initiates an
AsyncListener error notification, in which Spring MVC makes a completeWithError call.
This call, in turn, performs one final ASYNC dispatch to the application, during which Spring MVC
invokes the configured exception resolvers and completes the request.
SseEmitter (a subclass of ResponseBodyEmitter) provides support for
Server-Sent Events, where events sent from the server
are formatted according to the W3C SSE specification. To produce an SSE
stream from a controller, return SseEmitter, as the following example shows:
@GetMapping(path="/events", produces=MediaType.TEXT_EVENT_STREAM_VALUE)
public SseEmitter handle() {
SseEmitter emitter = new SseEmitter();
// Save the emitter somewhere..
return emitter;
}
// In some other thread
emitter.send("Hello once");
// and again later on
emitter.send("Hello again");
// and done at some point
emitter.complete();While SSE is the main option for streaming into browsers, note that Internet Explorer does not support Server-Sent Events. Consider using Spring’s WebSocket messaging with SockJS fallback transports (including SSE) that target a wide range of browsers.
See also previous section for notes on exception handling.
Sometimes, it is useful to bypass message conversion and stream directly to the response
OutputStream (for example, for a file download). You can use the StreamingResponseBody
return value type to do so, as the following example shows:
@GetMapping("/download")
public StreamingResponseBody handle() {
return new StreamingResponseBody() {
@Override
public void writeTo(OutputStream outputStream) throws IOException {
// write...
}
};
}You can use StreamingResponseBody as the body in a ResponseEntity to
customize the status and headers of the response.
Spring MVC supports use of reactive client libraries in a controller (also read
Reactive Libraries in the WebFlux section).
This includes the WebClient from spring-webflux and others, such as Spring Data
reactive data repositories. In such scenarios, it is convenient to be able to return
reactive types from the controller method.
Reactive return values are handled as follows:
-
A single-value promise is adapted to, similar to using
DeferredResult. Examples includeMono(Reactor) orSingle(RxJava). -
A multi-value stream with a streaming media type (such as
application/stream+jsonortext/event-stream) is adapted to, similar to usingResponseBodyEmitterorSseEmitter. Examples includeFlux(Reactor) orObservable(RxJava). Applications can also returnFlux<ServerSentEvent>orObservable<ServerSentEvent>. -
A multi-value stream with any other media type (such as
application/json) is adapted to, similar to usingDeferredResult<List<?>>.
|
Tip
|
Spring MVC supports Reactor and RxJava through the
{api-spring-framework}/core/ReactiveAdapterRegistry.html[ReactiveAdapterRegistry] from
spring-core, which lets it adapt from multiple reactive libraries.
|
For streaming to the response, reactive back pressure is supported, but writes to the
response are still blocking and are executed on a separate thread through the
configured TaskExecutor, to avoid
blocking the upstream source (such as a Flux returned from WebClient).
By default, SimpleAsyncTaskExecutor is used for the blocking writes, but that is not
suitable under load. If you plan to stream with a reactive type, you should use the
MVC configuration to configure a task executor.
The Servlet API does not provide any notification when a remote client goes away. Therefore, while streaming to the response, whether through SseEmitter or <<mvc-ann-async-reactive-types,reactive types>, it is important to send data periodically, since the write fails if the client has disconnected. The send could take the form of an empty (comment-only) SSE event or any other data that the other side would have to to interpret as a heartbeat and ignore.
Alternatively, consider using web messaging solutions (such as STOMP over WebSocket or WebSocket with SockJS) that have a built-in heartbeat mechanism.
The asynchronous request processing feature must be enabled at the Servlet container level. The MVC configuration also exposes several options for asynchronous requests.
Filter and Servlet declarations have an asyncSupported flag that needs to be set to true
to enable asynchronous request processing. In addition, Filter mappings should be
declared to handle the ASYNC javax.servlet.DispatchType.
In Java configuration, when you use AbstractAnnotationConfigDispatcherServletInitializer
to initialize the Servlet container, this is done automatically.
In web.xml configuration, you can add <async-supported>true</async-supported> to the
DispatcherServlet and to Filter declarations and add
<dispatcher>ASYNC</dispatcher> to filter mappings.
The MVC configuration exposes the following options related to asynchronous request processing:
-
Java configuration: Use the
configureAsyncSupportcallback onWebMvcConfigurer. -
XML namespace: Use the
<async-support>element under<mvc:annotation-driven>.
You can configure the following:
-
Default timeout value for async requests, which if not set, depends on the underlying Servlet container (for example, 10 seconds on Tomcat).
-
AsyncTaskExecutorto use for blocking writes when streaming with Reactive Types and for executingCallableinstances returned from controller methods. We highly recommended configuring this property if you stream with reactive types or have controller methods that returnCallable, since by default, it is aSimpleAsyncTaskExecutor. -
DeferredResultProcessingInterceptorimplementations andCallableProcessingInterceptorimplementations.
Note that you can also set the default timeout value on a DeferredResult,
a ResponseBodyEmitter, and an SseEmitter. For a Callable, you can use WebAsyncTask to provide
a timeout value.
The Spring Security project provides support for protecting web applications from malicious exploits. See the Spring Security reference documentation, including:
-
{doc-root}/spring-security/site/docs/current/reference/html5/#mvc[Spring MVC Security]
-
{doc-root}/spring-security/site/docs/current/reference/html5/#test-mockmvc[Spring MVC Test Support]
-
{doc-root}/spring-security/site/docs/current/reference/html5/#csrf[CSRF protection]
-
{doc-root}/spring-security/site/docs/current/reference/html5/#headers[Security Response Headers]
HDIV is another web security framework that integrates with Spring MVC.
HTTP caching can significantly improve the performance of a web application. HTTP caching
revolves around the Cache-Control response header and, subsequently, conditional request
headers (such as Last-Modified and ETag). Cache-Control advises private (for example, browser)
and public (for example, proxy) caches on how to cache and re-use responses. An ETag header is used
to make a conditional request that may result in a 304 (NOT_MODIFIED) without a body,
if the content has not changed. ETag can be seen as a more sophisticated successor to
the Last-Modified header.
This section describes the HTTP caching-related options that are available in Spring Web MVC.
{api-spring-framework}/http/CacheControl.html[CacheControl] provides support for
configuring settings related to the Cache-Control header and is accepted as an argument
in a number of places:
-
{api-spring-framework}/web/servlet/mvc/WebContentInterceptor.html[
WebContentInterceptor] -
{api-spring-framework}/web/servlet/support/WebContentGenerator.html[
WebContentGenerator]
While RFC 7234 describes all possible
directives for the Cache-Control response header, the CacheControl type takes a
use case-oriented approach that focuses on the common scenarios:
// 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();WebContentGenerator also accept a simpler cachePeriod property (defined in seconds) that
works as follows:
-
A
-1value does not generate aCache-Controlresponse header. -
A
0value prevents caching by using the'Cache-Control: no-store'directive. -
An
n > 0value caches the given response fornseconds by using the'Cache-Control: max-age=n'directive.
Controllers can add explicit support for HTTP caching. We recommended doing so, since the
lastModified or ETag value for a resource needs to be calculated before it can be compared
against conditional request headers. A controller can add an ETag header and Cache-Control
settings to a ResponseEntity, as the following example shows:
@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);
}The preceding example sends an 304 (NOT_MODIFIED) response with an empty body if the comparison
to the conditional request headers indicates that the content has not changed. Otherwise, the
ETag and Cache-Control headers are added to the response.
You can also make the check against conditional request headers in the controller, as the following example shows:
@RequestMapping
public String myHandleMethod(WebRequest webRequest, Model model) {
long eTag = ... (1)
if (request.checkNotModified(eTag)) {
return null; (2)
}
model.addAttribute(...); (3)
return "myViewName";
}-
Application-specific calculation.
-
The esponse has been set to 304 (NOT_MODIFIED) — no further processing.
-
Continue with the request processing.
There are three variants for checking conditional requests against eTag values, lastModified
values, or both. For conditional GET and HEAD requests, you can set the response to
304 (NOT_MODIFIED). For conditional POST, PUT, and DELETE, you can instead set the response
to 409 (PRECONDITION_FAILED), to prevent concurrent modification.
You should serve static resources with a Cache-Control and conditional response headers
for optimal performance. See the section on configuring Static Resources.
You can use the ShallowEtagHeaderFilter to add “shallow” eTag values that are computed from the
response content and, thus, save bandwidth but not CPU time. See Shallow ETag.
The MVC Java configuration and the MVC XML namespace provide default configuration suitable for most applications and a configuration API to customize it.
For more advanced customizations, which are 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 configuration and the MVC namespace. If you want to learn more, see Special Bean Types and Web MVC Config.
In Java configuration, you can use the @EnableWebMvc annotation to enable MVC
configuration, as the following example shows:
@Configuration
@EnableWebMvc
public class WebConfig {
}In XML configuration, you can use the <mvc:annotation-driven> element to enable MVC
configuration, as the following example shows:
<?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 preceding example registers a number of Spring MVC infrastructure beans and adapts to dependencies available on the classpath (for example, payload converters for JSON, XML, and others).
In Java configuration, you can implement the WebMvcConfigurer interface, as the
following example shows:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
// Implement configuration methods...
}In XML, you can check attributes and sub-elements of <mvc:annotation-driven/>. You can
view the Spring MVC XML schema or use
the code completion feature of your IDE to discover what attributes and
sub-elements are available.
By default formatters, for Number and Date types are installed, including support for
the @NumberFormat and @DateTimeFormat annotations. Full support for the Joda-Time
formatting library is also installed if Joda-Time is present on the classpath.
In Java configuration, you can register custom formatters and converters, as the following example shows:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addFormatters(FormatterRegistry registry) {
// ...
}
}The following example shows how to achieve the same configuration in XML:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<mvc:annotation-driven 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 the FormatterRegistrar SPI
and the FormattingConversionServiceFactoryBean for more information on when to use FormatterRegistrar implementations.
|
By default, if Bean Validation is present
on the classpath (for example, Hibernate Validator), the LocalValidatorFactoryBean is registered
as a global Validator for use with @Valid and Validated on
controller method arguments.
In Java configuration, you can customize the global Validator instance, as the
following example shows:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public Validator getValidator(); {
// ...
}
}The following example shows how to achieve the same configuration in XML:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:mvc="http://www.springframework.org/schema/mvc"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc.xsd">
<mvc:annotation-driven validator="globalValidator"/>
</beans>Note that you can also register Validator implementations locally, as the following
example shows:
@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 configuration.
|
In Java configuration, you can register interceptors to apply to incoming requests, as the following example shows:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(new LocaleChangeInterceptor());
registry.addInterceptor(new ThemeChangeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**");
registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*");
}
}The following example shows how to achieve the same configuration in XML:
<mvc:interceptors>
<bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"/>
<mvc:interceptor>
<mvc:mapping path="/**"/>
<mvc:exclude-mapping path="/admin/**"/>
<bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor"/>
</mvc:interceptor>
<mvc:interceptor>
<mvc:mapping path="/secure/*"/>
<bean class="org.example.SecurityInterceptor"/>
</mvc:interceptor>
</mvc:interceptors>You can configure how Spring MVC determines the requested media types from the request
(for example, Accept header, URL path extension, query parameter, and others).
By default, the URL path extension is checked first — with json, xml, rss, and atom
registered as known extensions (depending on classpath dependencies). 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 using the query parameter strategy over path extensions. See
Suffix Match and Suffix Match and RFD for
more details.
In Java configuration, you can customize requested content type resolution, as the following example shows:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
configurer.mediaType("json", MediaType.APPLICATION_JSON);
configurer.mediaType("xml", MediaType.APPLICATION_XML);
}
}The following example shows how to achieve the same configuration in XML:
<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>You can customize HttpMessageConverter in Java configuration by overriding
{api-spring-framework}/web/servlet/config/annotation/WebMvcConfigurer.html#configureMessageConverters-java.util.List-[configureMessageConverters()]
(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()]
(to customize the default converters or add additional converters to the default ones).
The following example adds XML and Jackson JSON converters with a customized
ObjectMapper instead of the 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.createXmlMapper(true).build()));
}
}In the preceding 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,
Which adds support for accessing parameter names (a feature added in Java 8).
This builder customizes Jackson’s default properties as follows:
-
DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIESis disabled. -
MapperFeature.DEFAULT_VIEW_INCLUSIONis disabled.
It also automatically registers the following well-known modules if they are detected on the classpath:
-
jackson-datatype-jdk7: Support for Java 7 types, such as
java.nio.file.Path. -
jackson-datatype-joda: Support for Joda-Time types.
-
jackson-datatype-jsr310: Support for Java 8 Date and Time API types.
-
jackson-datatype-jdk8: Support for other Java 8 types, such as
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:
-
jackson-datatype-money: Support for
javax.moneytypes (unofficial module). -
jackson-datatype-hibernate: Support for Hibernate-specific types and properties (including lazy-loading aspects).
The following example shows how to achieve the same configuration in XML:
<mvc:annotation-driven>
<mvc:message-converters>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="objectMapper" ref="objectMapper"/>
</bean>
<bean class="org.springframework.http.converter.xml.MappingJackson2XmlHttpMessageConverter">
<property name="objectMapper" ref="xmlMapper"/>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
<bean id="objectMapper" class="org.springframework.http.converter.json.Jackson2ObjectMapperFactoryBean"
p:indentOutput="true"
p:simpleDateFormat="yyyy-MM-dd"
p:modulesToInstall="com.fasterxml.jackson.module.paramnames.ParameterNamesModule"/>
<bean id="xmlMapper" parent="objectMapper" p:createXmlMapper="true"/>This is a shortcut for defining a ParameterizableViewController that immediately
forwards to a view when invoked. You can use it in static cases when there is no Java controller
logic to execute before the view generates the response.
The following example of Java configuration forwards a request for / to a view called home:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addViewControllers(ViewControllerRegistry registry) {
registry.addViewController("/").setViewName("home");
}
}The following example achieves the same thing as the preceding example, but with XML, by
using the <mvc:view-controller> element:
<mvc:view-controller path="/" view-name="home"/>The MVC configuration simplifies the registration of view resolvers.
The following Java configuration example configures content negotiation view
resolution by using JSP and Jackson as a default View for JSON rendering:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureViewResolvers(ViewResolverRegistry registry) {
registry.enableContentNegotiation(new MappingJackson2JsonView());
registry.jsp();
}
}The following example shows how to achieve the same configuration 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. The following example works 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 configuration, you can add the respective Configurer bean,
as the following example shows:
@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("/freemarker");
return configurer;
}
}This option provides a convenient way to serve static resources from a list of
{api-spring-framework}/core/io/Resource.html[Resource]-based locations.
In the next example, 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 one-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.
The following listing shows how to do so with Java configuration:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**")
.addResourceLocations("/public", "classpath:/static/")
.setCachePeriod(31556926);
}
}The following example shows how to achieve the same configuration in XML:
<mvc:resources mapping="/resources/**"
location="/public, classpath:/static/"
cache-period="31556926" />The resource handler also supports a chain of
{api-spring-framework}/web/servlet/resource/ResourceResolver.html[ResourceResolver] implementations and
{api-spring-framework}/web/servlet/resource/ResourceTransformer.html[ResourceTransformer] implementations,
which you can use to create a toolchain for working with optimized resources.
You can use the VersionResourceResolver 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.
The following example shows how to use VersionResourceResolver in Java configuration:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
registry.addResourceHandler("/resources/**")
.addResourceLocations("/public/")
.resourceChain(true)
.addResolver(new VersionResourceResolver().addContentVersionStrategy("/**"));
}
}The following example shows how to achieve the same configuration in XML:
<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 then use ResourceUrlProvider to rewrite URLs and apply the full chain of resolvers and
transformers — for example, to insert versions. The MVC configuration provides a ResourceUrlProvider
bean so that 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.
Note that, when using both EncodedResourceResolver (for example, for serving gzipped or
brotli-encoded resources) and VersionedResourceResolver, you must register them in this order.
That ensures content-based versions are always computed reliably, based on the unencoded file.
WebJars is also supported through WebJarsResourceResolver
and is 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 — for example, /jquery/jquery.min.js to
/jquery/1.2.0/jquery.min.js.
Spring MVC 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 forwards all requests to the default Servlet. Therefore, it must
remain last in the order of all other URL HandlerMappings. That is the
case if you use <mvc:annotation-driven>. Alternatively, if you set 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.
The following example shows how to enable the feature by using the default setup:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable();
}
}The following example shows how to achieve the same configuration 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 tries 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 you must explicitly provide the default Servlet’s name, as the following example shows:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
configurer.enable("myCustomDefaultServlet");
}
}The following example shows how to achieve the same configuration in XML:
<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>You can customize options related to path matching and treatment of the URL.
For details on the individual options, see the
{api-spring-framework}/web/servlet/config/annotation/PathMatchConfigurer.html[PathMatchConfigurer] javadoc.
The following example shows how to customize path matching in Java configuration:
@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {
@Override
public void configurePathMatch(PathMatchConfigurer configurer) {
configurer
.setUseSuffixPatternMatch(true)
.setUseTrailingSlashMatch(false)
.setUseRegisteredSuffixPatternMatch(true)
.setPathMatcher(antPathMatcher())
.setUrlPathHelper(urlPathHelper())
.addPathPrefix("/api",
HandlerTypePredicate.forAnnotation(RestController.class));
}
@Bean
public UrlPathHelper urlPathHelper() {
//...
}
@Bean
public PathMatcher antPathMatcher() {
//...
}
}The following example shows how to achieve the same configuration in XML:
<mvc:annotation-driven>
<mvc:path-matching
suffix-pattern="true"
trailing-slash="false"
registered-suffixes-only="true"
path-helper="pathHelper"
path-matcher="pathMatcher"/>
</mvc:annotation-driven>
<bean id="pathHelper" class="org.example.app.MyPathHelper"/>
<bean id="pathMatcher" class="org.example.app.MyPathMatcher"/>@EnableWebMvc imports DelegatingWebMvcConfiguration, which:
-
Provides default Spring configuration for Spring MVC applications
-
Detects and delegates to
WebMvcConfigurerimplementations to customize that configuration.
For advanced mode, you can remove @EnableWebMvc and extend directly from
DelegatingWebMvcConfiguration instead of implementing WebMvcConfigurer,
as the following example shows:
@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 implementations on
the classpath.
The MVC namespace does not have an advanced mode. If you need to customize a property on
a bean that you cannot change otherwise, you can use the BeanPostProcessor lifecycle
hook of the Spring ApplicationContext, as the following example shows:
@Component
public class MyPostProcessor implements BeanPostProcessor {
public Object postProcessBeforeInitialization(Object bean, String name) throws BeansException {
// ...
}
}Note that you need to declare MyPostProcessor as a bean, either explicitly in XML or
by letting it be detected through a <component-scan/> declaration.
Servlet 4 containers are required to support HTTP/2, and Spring Framework 5 is compatible with Servlet API 4. From a programming model perspective, there is nothing specific that applications need to do. However, there are considerations related to server configuration. For more details, see the HTTP/2 wiki page.
The Servlet API does expose one construct related to HTTP/2. You can use the
javax.servlet.http.PushBuilder proactively push resources to clients, and it
is supported as a method argument to @RequestMapping methods.