/*
* Copyright 2002-2016 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;
import org.springframework.web.method.HandlerMethod;
/**
* Extends {@code HandlerInterceptor} with a callback method invoked after the
* start of asynchronous request handling.
*
* <p>When a handler starts an asynchronous request, the {@link DispatcherServlet}
* exits without invoking {@code postHandle} and {@code afterCompletion} as it
* normally does for a synchronous request, since the result of request handling
* (e.g. ModelAndView) is likely not yet ready and will be produced concurrently
* from another thread. In such scenarios, {@link #afterConcurrentHandlingStarted}
* is invoked instead, allowing implementations to perform tasks such as cleaning
* up thread-bound attributes before releasing the thread to the Servlet container.
*
* <p>When asynchronous handling completes, the request is dispatched to the
* container for further processing. At this stage the {@code DispatcherServlet}
* invokes {@code preHandle}, {@code postHandle}, and {@code afterCompletion}.
* To distinguish between the initial request and the subsequent dispatch
* after asynchronous handling completes, interceptors can check whether the
* {@code javax.servlet.DispatcherType} of {@link javax.servlet.ServletRequest}
* is {@code "REQUEST"} or {@code "ASYNC"}.
*
* <p>Note that {@code HandlerInterceptor} implementations may need to do work
* when an async request times out or completes with a network error. For such
* cases the Servlet container does not dispatch and therefore the
* {@code postHandle} and {@code afterCompletion} methods will not be invoked.
* Instead, interceptors can register to track an asynchronous request through
* the {@code registerCallbackInterceptor} and {@code registerDeferredResultInterceptor}
* methods on {@link org.springframework.web.context.request.async.WebAsyncManager
* WebAsyncManager}. This can be done proactively on every request from
* {@code preHandle} regardless of whether async request processing will start.
*
* @author Rossen Stoyanchev
* @since 3.2
* @see org.springframework.web.context.request.async.WebAsyncManager
* @see org.springframework.web.context.request.async.CallableProcessingInterceptor
* @see org.springframework.web.context.request.async.DeferredResultProcessingInterceptor
*/
public interface AsyncHandlerInterceptor extends HandlerInterceptor {
/**
* Called instead of {@code postHandle} and {@code afterCompletion}, when
* the a handler is being executed concurrently.
* <p>Implementations may use the provided request and response but should
* avoid modifying them in ways that would conflict with the concurrent
* execution of the handler. A typical use of this method would be to
* clean up thread-local variables.
* @param request the current request
* @param response the current response
* @param handler the handler (or {@link HandlerMethod}) that started async
* execution, for type and/or instance examination
* @throws Exception in case of errors
*/
void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler)
throws Exception;
}