org.springframework.web.servlet
Interface HandlerInterceptor

All Known Implementing Classes:

HandlerInterceptorAdapter, OpenSessionInViewInterceptor, WebContentInterceptor

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.

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 2.3 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(org.springframework.web.servlet.HandlerInterceptor[]), UserRoleAuthorizationInterceptor, LocaleChangeInterceptor, ThemeChangeInterceptor, Filter

Method Summary

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

public 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

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

modelAndView - the ModelAndView that the handler returned, can also be null

Throws:

Exception - in case of errors

afterCompletion

public 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!

Parameters:

request - current HTTP request

response - current HTTP response

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

ex - exception thrown on handler execution, if any (only included as additional context information for the case where a handler threw an exception; request execution may have failed even when this argument is null)

Throws:

Exception - in case of errors