org.springframework.web.servlet

Interface HandlerInterceptor

All Known Subinterfaces:

AsyncHandlerInterceptor

All Known Implementing Classes:

ConversionServiceExposingInterceptor, HandlerInterceptorAdapter, LocaleChangeInterceptor, ResourceUrlProviderExposingInterceptor, ThemeChangeInterceptor, UserRoleAuthorizationInterceptor, WebContentInterceptor, WebRequestHandlerInterceptorAdapter

public interface HandlerInterceptor

Workflow interface that allows for customized handler execution chains. Applications can register any number of existing or custom interceptors for certain groups of handlers, to add common preprocessing behavior without needing to modify each handler implementation.

A HandlerInterceptor gets called before the appropriate HandlerAdapter triggers the execution of the handler itself. This mechanism can be used for a large field of preprocessing aspects, e.g. for authorization checks, or common handler behavior like locale or theme changes. Its main purpose is to allow for factoring out repetitive handler code.

In an async processing scenario, the handler may be executed in a separate thread while the main thread exits without rendering or invoking the postHandle and afterCompletion callbacks. When concurrent handler execution completes, the request is dispatched back in order to proceed with rendering the model and all methods of this contract are invoked again. For further options and details see org.springframework.web.servlet.AsyncHandlerInterceptor

Typically an interceptor chain is defined per HandlerMapping bean, sharing its granularity. To be able to apply a certain interceptor chain to a group of handlers, one needs to map the desired handlers via one HandlerMapping bean. The interceptors themselves are defined as beans in the application context, referenced by the mapping bean definition via its "interceptors" property (in XML: a <list> of <ref>).

HandlerInterceptor is basically similar to a Servlet Filter, but in contrast to the latter it just allows custom pre-processing with the option of prohibiting the execution of the handler itself, and custom post-processing. Filters are more powerful, for example they allow for exchanging the request and response objects that are handed down the chain. Note that a filter gets configured in web.xml, a HandlerInterceptor in the application context.

As a basic guideline, fine-grained handler-related preprocessing tasks are candidates for HandlerInterceptor implementations, especially factored-out common handler code and authorization checks. On the other hand, a Filter is well-suited for request content and view content handling, like multipart forms and GZIP compression. This typically shows when one needs to map the filter to certain content types (e.g. images), or to all requests.

Since:

20.06.2003

Author:

Juergen Hoeller

See Also:

HandlerExecutionChain.getInterceptors(), HandlerInterceptorAdapter, AbstractHandlerMapping.setInterceptors(java.lang.Object[]), UserRoleAuthorizationInterceptor, LocaleChangeInterceptor, ThemeChangeInterceptor, Filter

Method Summary

Modifier and Type	Method and Description
void	afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) Callback after completion of request processing, that is, after rendering the view.
void	postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) Intercept the execution of a handler.
boolean	preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) Intercept the execution of a handler.

Method Detail

preHandle

boolean preHandle(HttpServletRequest request,
                  HttpServletResponse response,
                  Object handler)
           throws Exception

Intercept the execution of a handler. Called after HandlerMapping determined an appropriate handler object, but before HandlerAdapter invokes the handler.

DispatcherServlet processes a handler in an execution chain, consisting of any number of interceptors, with the handler itself at the end. With this method, each interceptor can decide to abort the execution chain, typically sending a HTTP error or writing a custom response.

Parameters:

request - current HTTP request

response - current HTTP response

handler - chosen handler to execute, for type and/or instance evaluation

Returns:

true if the execution chain should proceed with the next interceptor or the handler itself. Else, DispatcherServlet assumes that this interceptor has already dealt with the response itself.

Throws:

Exception - in case of errors

postHandle

void postHandle(HttpServletRequest request,
                HttpServletResponse response,
                Object handler,
                ModelAndView modelAndView)
         throws Exception

Intercept the execution of a handler. Called after HandlerAdapter actually invoked the handler, but before the DispatcherServlet renders the view. Can expose additional model objects to the view via the given ModelAndView.

DispatcherServlet processes a handler in an execution chain, consisting of any number of interceptors, with the handler itself at the end. With this method, each interceptor can post-process an execution, getting applied in inverse order of the execution chain.

Parameters:

request - current HTTP request

response - current HTTP response

handler - handler (or HandlerMethod) that started async execution, for type and/or instance examination

modelAndView - the ModelAndView that the handler returned (can also be null)

Throws:

Exception - in case of errors

afterCompletion

void afterCompletion(HttpServletRequest request,
                     HttpServletResponse response,
                     Object handler,
                     Exception ex)
              throws Exception

Callback after completion of request processing, that is, after rendering the view. Will be called on any outcome of handler execution, thus allows for proper resource cleanup.

Note: Will only be called if this interceptor's preHandle method has successfully completed and returned true!

As with the postHandle method, the method will be invoked on each interceptor in the chain in reverse order, so the first interceptor will be the last to be invoked.

Parameters:

request - current HTTP request

response - current HTTP response

handler - handler (or HandlerMethod) that started async execution, for type and/or instance examination

ex - exception thrown on handler execution, if any

Throws:

Exception - in case of errors