/*
* Copyright 2002-2006 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* 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.
*
* <p>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.
*
* <p>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>).
*
* <p>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.
*
* <p>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.
*
* @author Juergen Hoeller
* @since 20.06.2003
* @see HandlerExecutionChain#getInterceptors
* @see org.springframework.web.servlet.handler.HandlerInterceptorAdapter
* @see org.springframework.web.servlet.handler.AbstractHandlerMapping#setInterceptors
* @see org.springframework.web.servlet.handler.UserRoleAuthorizationInterceptor
* @see org.springframework.web.servlet.i18n.LocaleChangeInterceptor
* @see org.springframework.web.servlet.theme.ThemeChangeInterceptor
* @see javax.servlet.Filter
*/
public interface HandlerInterceptor {
/**
* Intercept the execution of a handler. Called after HandlerMapping determined
* an appropriate handler object, but before HandlerAdapter invokes the handler.
* <p>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.
* @param request current HTTP request
* @param response current HTTP response
* @param handler chosen handler to execute, for type and/or instance evaluation
* @return <code>true</code> 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
*/
boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
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.
* <p>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.
* @param request current HTTP request
* @param response current HTTP response
* @param handler chosen handler to execute, for type and/or instance examination
* @param modelAndView the <code>ModelAndView</code> that the handler returned
* (can also be <code>null</code>)
* @throws Exception in case of errors
*/
void postHandle(
HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
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.
* <p>Note: Will only be called if this interceptor's <code>preHandle</code>
* method has successfully completed and returned <code>true</code>!
* <p>As with the {@code 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.
* @param request current HTTP request
* @param response current HTTP response
* @param handler chosen handler to execute, for type and/or instance examination
* @param ex exception thrown on handler execution, if any
* @throws Exception in case of errors
*/
void afterCompletion(
HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
throws Exception;
}
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