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

爱被打了一巴掌 2022-07-14 12:42 195阅读 0赞

在上一篇博客[springMVC源码分析--HandlerInterceptor拦截器（一）][springMVC_--HandlerInterceptor]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;
    				}
    // 调用具体的Controller中的处理方法Actually invoke the handler. mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
    				......
    				//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。

[springMVC_--HandlerInterceptor]: http://blog.csdn.net/qq924862077/article/details/53524507