springMVC源碼分析--HandlerInterceptor攔截器調用過程（二）

在上一篇部落格​​springMVC源碼分析--HandlerInterceptor攔截器（一）​​中我們介紹了HandlerInterceptor攔截器相關的内容，了解到了HandlerInterceptor提供的三個接口方法：

（1）preHandle: 在執行controller處理之前執行，傳回值為boolean ,傳回值為true時接着執行postHandle和afterCompletion，如果我們傳回false則中斷執行

（2）postHandle:在執行controller的處理後，在ModelAndView處理前執行

（3）afterCompletion ：在DispatchServlet執行完ModelAndView之後執行

我們可以看到這三個方法的調用過程是不一樣的，接下來我們分析一下這個三個方法具體調用實作的地方。其最終實作調用的地方是在doDispatch函數中，因為doDispatch完成了一個請求到傳回資料的完整操作。

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

    HandlerExecutionChain mappedHandler = null;
    
    .......

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

      try {
        
        .......
        //擷取HandlerExecutionChain
        mappedHandler = getHandler(processedRequest);
        
        ......
        //最終會調用HandlerInterceptor的preHandle方法
        if (!mappedHandler.applyPreHandle(processedRequest, response)) {
          return;
        }
// 調用具體的Controller中的處理方法Actually invoke the handler.
mv = ha.handle(processedRequest, response, mappedHandler.getHandler());      

mappedHandler.applyPreHandle(processedRequest, response)：最終會調用HandlerInterceptor的preHandle方法。在HandlerExecutionChain中的具體實作如下，我們可以看到會調用所有的HandlerInterceptor攔截器并調用其preHandler方法。

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

mappedHandler.applyPostHandle(processedRequest, response, mv)：最終會調用HandlerInterceptor的postHandle方法

具體實作是在HandlerExecutionChain中實作如下，就是擷取所有的攔截器并調用其postHandle方法。

void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
    HandlerInterceptor[] interceptors = getInterceptors();//擷取所有攔截器
    if (!ObjectUtils.isEmpty(interceptors)) {
      for (int i = interceptors.length - 1; i >= 0; i--) {
        HandlerInterceptor interceptor = interceptors[i];
        interceptor.postHandle(request, response, this.handler, mv);//分别調用攔截器的postHandle方法
      }
    }
  }      

triggerAfterCompletion(processedRequest, response, mappedHandler, ex)：最終會調用HandlerInterceptor的afterCompletion 方法

triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err)：

最終會調用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();//擷取所有攔截器
    if (!ObjectUtils.isEmpty(interceptors)) {
      for (int i = this.interceptorIndex; i >= 0; i--) {
        HandlerInterceptor interceptor = interceptors[i];
        try {
          interceptor.afterCompletion(request, response, this.handler, ex);//調用攔截器的afterCompletion方法
        }
        catch (Throwable ex2) {
          logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
        }
      }
    }
  }