springMVC源码分析--HandlerInterceptor拦截器调用过程（二）

在上一篇博客springMVC源码分析--HandlerInterceptor拦截器（一）中我们介绍了HandlerInterceptor拦截器相关的内容，了解到了HandlerInterceptor提供的三个接口方法：

（1）preHandle: 在执行controller处理之前执行，返回值为boolean ,返回值为true时接着执行postHandle和afterCompletion，如果我们返回false则中断执行
（2）postHandle:在执行controller的处理后，在ModelAndView处理前执行
（3）afterCompletion ：在DispatchServlet执行完ModelAndView之后执行

我们可以看到这三个方法的调用过程是不一样的，接下来我们分析一下这个三个方法具体调用实现的地方。其最终实现调用的地方是在doDispatch函数中，因为doDispatch完成了一个请求到返回数据的完整操作。

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {

		HandlerExecutionChain mappedHandler = null;

		.......

		try {
			ModelAndView mv = null;
			Exception dispatchException = null;

			try {

				.......
				//获取HandlerExecutionChain
				mappedHandler = getHandler(processedRequest);

				......
				//最终会调用HandlerInterceptor的preHandle方法
				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

				......
				//最终会调用HandlerInterceptor的postHandle方法
				mappedHandler.applyPostHandle(processedRequest, response, mv);
			}
			catch (Exception ex) {
				dispatchException = ex;
			}
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
			//最终会调用HandlerInterceptor的afterCompletion 方法
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Error err) {
			//最终会调用HandlerInterceptor的afterCompletion 方法
			triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err);
		}
		finally {
			if (asyncManager.isConcurrentHandlingStarted()) {
				// Instead of postHandle and afterCompletion
				if (mappedHandler != null) {
					mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
				}
			}
			else {
				// Clean up any resources used by a multipart request.
				if (multipartRequestParsed) {
					cleanupMultipart(processedRequest);
				}
			}
		}
	}

mappedHandler.applyPreHandle(processedRequest, response)：最终会调用HandlerInterceptor的preHandle方法。在HandlerExecutionChain中的具体实现如下，我们可以看到会调用所有的HandlerInterceptor拦截器并调用其preHandler方法。

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();//获取所有的拦截器
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = 0; i < interceptors.length; i++) {
				HandlerInterceptor interceptor = interceptors[i];
				if (!interceptor.preHandle(request, response, this.handler)) {//分别调用拦截器的preHandle方法
					triggerAfterCompletion(request, response, null);
					return false;
				}
				this.interceptorIndex = i;
			}
		}
		return true;
	}

mappedHandler.applyPostHandle(processedRequest, response, mv)：最终会调用HandlerInterceptor的postHandle方法

具体实现是在HandlerExecutionChain中实现如下，就是获取所有的拦截器并调用其postHandle方法。

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
		HandlerInterceptor[] interceptors = getInterceptors();//获取所有拦截器
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = interceptors.length - 1; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				interceptor.postHandle(request, response, this.handler, mv);//分别调用拦截器的postHandle方法
			}
		}
	}

triggerAfterCompletion(processedRequest, response, mappedHandler, ex)：最终会调用HandlerInterceptor的afterCompletion 方法
triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err)：最终会调用HandlerInterceptor的afterCompletion 方法

private void triggerAfterCompletionWithError(HttpServletRequest request, HttpServletResponse response,
			HandlerExecutionChain mappedHandler, Error error) throws Exception {

		ServletException ex = new NestedServletException("Handler processing failed", error);
		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, ex);
		}
		throw ex;
	}

private void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response,
			HandlerExecutionChain mappedHandler, Exception ex) throws Exception {

		if (mappedHandler != null) {
			mappedHandler.triggerAfterCompletion(request, response, ex);
		}
		throw ex;
	}

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
			throws Exception {

		HandlerInterceptor[] interceptors = getInterceptors();//获取所有拦截器
		if (!ObjectUtils.isEmpty(interceptors)) {
			for (int i = this.interceptorIndex; i >= 0; i--) {
				HandlerInterceptor interceptor = interceptors[i];
				try {
					interceptor.afterCompletion(request, response, this.handler, ex);//调用拦截器的afterCompletion方法
				}
				catch (Throwable ex2) {
					logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
				}
			}
		}
	}

通过以上代码分析我们可以看到HandlerInterceptor拦截器的最终调用实现是在DispatcherServlet的doDispatch方法中，并且SpringMVC提供了HandlerExecutionChain来帮助我们执行所有配置的HandlerInterceptor拦截器，并分别调用HandlerInterceptor所提供的方法。