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;
        }
// 调用具体的Controller中的处理方法Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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。