拦截器调用原理

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HandlerInterceptor[] interceptors = getInterceptors();
　　　　　//遍历所有拦截器
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = 0; i < interceptors.length; i++) {
                HandlerInterceptor interceptor = interceptors[i];
　　　　　　　　　 
                if (!interceptor.preHandle(request, response, this.handler)) {
　　　　　　　　　　　　//当前拦截器拦截到执行之前所有拦截器的后置方法;
                    triggerAfterCompletion(request, response, null);
　　　　　　　　　　　　//表示有拦截器没有通过
                    return false;
                }
                this.interceptorIndex = i;
            }
        }
　　　　 //所有拦截器放行
        return true;
    }

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
   HttpServletRequest processedRequest = request;
   HandlerExecutionChain mappedHandler = null;
   boolean multipartRequestParsed = false;

   WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

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

      try {
         processedRequest = checkMultipart(request);
         multipartRequestParsed = (processedRequest != request);

         // Determine handler for the current request.
         mappedHandler = getHandler(processedRequest);
         if (mappedHandler == null || mappedHandler.getHandler() == null) {
            noHandlerFound(processedRequest, response);
            return;
         }

         // Determine handler adapter for the current request.
         HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

         // Process last-modified header, if supported by the handler.
         String method = request.getMethod();
         boolean isGet = "GET".equals(method);
         if (isGet || "HEAD".equals(method)) {
            long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
            if (logger.isDebugEnabled()) {
               logger.debug("Last-Modified value for [" + getRequestUri(request) + "] is: " + lastModified);
            }
            if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
               return;
            }
         }
　　　　　//只要有一个拦截器没有放行这里就返回;
         if (!mappedHandler.applyPreHandle(processedRequest, response)) {
            return;
         }
　　　　　　//所有拦截器放行执行目标方法
         // Actually invoke the handler.
         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
　　　　
         if (asyncManager.isConcurrentHandlingStarted()) {
            return;
         }
　　　　
         applyDefaultViewName(processedRequest, mv);
　　　　　　//后置增强;
         mappedHandler.applyPostHandle(processedRequest, response, mv);
      }
      catch (Exception ex) {
         dispatchException = ex;
      }
      catch (Throwable err) {
         // As of 4.3, we're processing Errors thrown from handler methods as well,
         // making them available for @ExceptionHandler methods and other scenarios.
         dispatchException = new NestedServletException("Handler dispatch failed", err);
      }
      processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
   }
   catch (Exception ex) {
      triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
   }
   catch (Throwable err) {
      triggerAfterCompletion(processedRequest, response, mappedHandler,
            new NestedServletException("Handler processing failed", 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);
         }
      }
   }
}

也就是说只要拦截器没有通过那么任何一个后置方法都不会执行;
但是会执行每个拦截器的

afterCompletion