注释类型 RequestMapping

NOTE: The set of features supported for Servlets is a superset of the set of features supported for Portlets. The places where this applies are marked with the label "Servlet-only" in this source file. For Servlet environments there are some further distinctions depending on whether an application is configured with "@MVC 3.0" or "@MVC 3.1" support classes. The places where this applies are marked with "@MVC 3.1-only" in this source file. For more details see the note on the new support classes added in Spring MVC 3.1 further below.

Handler methods which are annotated with this annotation are allowed to have very flexible signatures. They may have parameters of the following types, in arbitrary order (except for validation results, which need to follow right after the corresponding command object, if desired):

• Request and/or response objects (Servlet API or Portlet API). You may choose any specific request/response type, e.g. ServletRequest / HttpServletRequest or PortletRequest / ActionRequest / RenderRequest. Note that in the Portlet case, an explicitly declared action/render argument is also used for mapping specific request types onto a handler method (in case of no other information given that differentiates between action and render requests).
• Session object (Servlet API or Portlet API): either HttpSession or PortletSession. An argument of this type will enforce the presence of a corresponding session. As a consequence, such an argument will never be null. Note that session access may not be thread-safe, in particular in a Servlet environment: Consider switching the "synchronizeOnSession" flag to "true" if multiple requests are allowed to access a session concurrently.
• WebRequest or NativeWebRequest. Allows for generic request parameter access as well as request/session attribute access, without ties to the native Servlet/Portlet API.
• Locale for the current request locale (determined by the most specific locale resolver available, i.e. the configured LocaleResolver in a Servlet environment and the portal locale in a Portlet environment).
• InputStream / Reader for access to the request's content. This will be the raw InputStream/Reader as exposed by the Servlet/Portlet API.
• OutputStream / Writer for generating the response's content. This will be the raw OutputStream/Writer as exposed by the Servlet/Portlet API.
• HttpMethod for the HTTP request method
• @PathVariable annotated parameters (Servlet-only) for access to URI template values (i.e. /hotels/{hotel}). Variable values will be converted to the declared method argument type. By default, the URI template will match against the regular expression [^\.]* (i.e. any character other than period), but this can be changed by specifying another regular expression, like so: /hotels/{hotel:\d+}. Additionally, @PathVariable can be used on a Map<String, String> to gain access to all URI template variables.
• @MatrixVariable annotated parameters (Servlet-only) for access to name-value pairs located in URI path segments. Matrix variables must be represented with a URI template variable. For example /hotels/{hotel} where the incoming URL may be "/hotels/42;q=1". Additionally, @MatrixVariable can be used on a Map<String, String> to gain access to all matrix variables in the URL or to those in a specific path variable.
• @RequestParam annotated parameters for access to specific Servlet/Portlet request parameters. Parameter values will be converted to the declared method argument type. Additionally, @RequestParam can be used on a Map<String, String> or MultiValueMap<String, String> method parameter to gain access to all request parameters.
• @RequestHeader annotated parameters for access to specific Servlet/Portlet request HTTP headers. Parameter values will be converted to the declared method argument type. Additionally, @RequestHeader can be used on a Map<String, String>, MultiValueMap<String, String>, or HttpHeaders method parameter to gain access to all request headers.
• @RequestBody annotated parameters (Servlet-only) for access to the Servlet request HTTP contents. The request stream will be converted to the declared method argument type using message converters. Such parameters may optionally be annotated with @Valid and also support access to validation results through an Errors argument. Instead a MethodArgumentNotValidException exception is raised.
• @RequestPart annotated parameters (Servlet-only, @MVC 3.1-only) for access to the content of a part of "multipart/form-data" request. The request part stream will be converted to the declared method argument type using message converters. Such parameters may optionally be annotated with @Valid and support access to validation results through a Errors argument. Instead a MethodArgumentNotValidException exception is raised.
• @SessionAttribute annotated parameters for access to existing, permanent session attributes (e.g. user authentication object) as opposed to model attributes temporarily stored in the session as part of a controller workflow via SessionAttributes.
• @RequestAttribute annotated parameters for access to request attributes.
• HttpEntity<?> parameters (Servlet-only) for access to the Servlet request HTTP headers and contents. The request stream will be converted to the entity body using message converters.
• Map / Model / ModelMap for enriching the implicit model that will be exposed to the web view.
• RedirectAttributes (Servlet-only, @MVC 3.1-only) to specify the exact set of attributes to use in case of a redirect and also to add flash attributes (attributes stored temporarily on the server-side to make them available to the request after the redirect). RedirectAttributes is used instead of the implicit model if the method returns a "redirect:" prefixed view name or RedirectView.
• Command/form objects to bind parameters to: as bean properties or fields, with customizable type conversion, depending on InitBinder methods and/or the HandlerAdapter configuration - see the "webBindingInitializer" property on RequestMappingHandlerMethodAdapter. Such command objects along with their validation results will be exposed as model attributes, by default using the non-qualified command class name in property notation (e.g. "orderAddress" for type "mypackage.OrderAddress"). Specify a parameter-level @ModelAttribute annotation for declaring a specific model attribute name.
• Errors / BindingResult validation results for a preceding command/form object (the immediate preceding argument).
• SessionStatus status handle for marking form processing as complete (triggering the cleanup of session attributes that have been indicated by the @SessionAttributes annotation at the handler type level).
• UriComponentsBuilder (Servlet-only, @MVC 3.1-only) for preparing a URL relative to the current request's host, port, scheme, context path, and the literal part of the servlet mapping.

Note: Java 8's java.util.Optional is supported as a method parameter type with annotations that provide a required attribute (e.g. @RequestParam, @RequestHeader, etc.). The use of java.util.Optional in those cases is equivalent to having required=false.

The following return types are supported for handler methods:

• A ModelAndView object (Servlet MVC or Portlet MVC), with the model implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods.
• A Model object, with the view name implicitly determined through a RequestToViewNameTranslator and the model implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods.
• A Map object for exposing a model, with the view name implicitly determined through a RequestToViewNameTranslator and the model implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods.
• A View object, with the model implicitly determined through command objects and @ModelAttribute annotated reference data accessor methods. The handler method may also programmatically enrich the model by declaring a Model argument (see above).
• A String value which is interpreted as view name, with the model implicitly determined through command objects and @ModelAttribute annotated reference data accessor methods. The handler method may also programmatically enrich the model by declaring a ModelMap argument (see above).
• @ResponseBody annotated methods (Servlet-only) for access to the Servlet response HTTP contents. The return value will be converted to the response stream using message converters.
• An HttpEntity<?> or ResponseEntity<?> object (Servlet-only) to access to the Servlet response HTTP headers and contents. The entity body will be converted to the response stream using message converters.
• An HttpHeaders object to return a response with no body.
• A Callable which is used by Spring MVC to obtain the return value asynchronously in a separate thread transparently managed by Spring MVC on behalf of the application.
• A DeferredResult which the application uses to produce a return value in a separate thread of its own choosing, as an alternative to returning a Callable.
• A ListenableFuture which the application uses to produce a return value in a separate thread of its own choosing, as an alternative to returning a Callable.
• A CompletionStage (implemented by CompletableFuture for example) which the application uses to produce a return value in a separate thread of its own choosing, as an alternative to returning a Callable.
• A ResponseBodyEmitter can be used to write multiple objects to the response asynchronously; also supported as the body within ResponseEntity.
• An SseEmitter can be used to write Server-Sent Events to the response asynchronously; also supported as the body within ResponseEntity.
• A StreamingResponseBody can be used to write to the response asynchronously; also supported as the body within ResponseEntity.
• void if the method handles the response itself (by writing the response content directly, declaring an argument of type ServletResponse / HttpServletResponse / RenderResponse for that purpose) or if the view name is supposed to be implicitly determined through a RequestToViewNameTranslator (not declaring a response argument in the handler method signature; only applicable in a Servlet environment).
• Any other return type will be considered as single model attribute to be exposed to the view, using the attribute name specified through @ModelAttribute at the method level (or the default attribute name based on the return type's class name otherwise). The model will be implicitly enriched with command objects and the results of @ModelAttribute annotated reference data accessor methods.

NOTE:@RequestMapping will only be processed if an an appropriate HandlerMapping-HandlerAdapter pair is configured. This is the case by default in both the DispatcherServlet and the DispatcherPortlet. However, if you are defining custom HandlerMappings or HandlerAdapters, then you need to add DefaultAnnotationHandlerMapping and AnnotationMethodHandlerAdapter to your configuration..

NOTE: Spring 3.1 introduced a new set of support classes for @RequestMapping methods in Servlet environments called RequestMappingHandlerMapping and RequestMappingHandlerAdapter. They are recommended for use and even required to take advantage of new features in Spring MVC 3.1 (search "@MVC 3.1-only" in this source file) and going forward. The new support classes are enabled by default from the MVC namespace and with use of the MVC Java config (@EnableWebMvc) but must be configured explicitly if using neither.

NOTE: When using controller interfaces (e.g. for AOP proxying), make sure to consistently put all your mapping annotations - such as @RequestMapping and @SessionAttributes - on the controller interface rather than on the implementation class.