一次请求在SpringMVC核心执行流程

 

org.springframework.web.servlet.DispatcherServlet#doDispatch

1.1 获取执行调用链HandlerExecutionChain
1.2 获取处理器适配器HandlerAdapter
1.3 调用拦截器preHandle
1.4 调用适配器的handle方法
1.5 处理视图名
1.6 调用postHandle方法
1.7 视图渲染

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 {

         // 检查是否多模块请求
         processedRequest = checkMultipart(request);
         multipartRequestParsed = (processedRequest != request);

         // Determine handler for the current request.

         // 通过HandlerMapping根据url获取HandlerMethod, 再获取拦截器, 组合起来创建出调用执行链HandlerExecutionChain对象(HandlerMethod + 拦截器)
         mappedHandler = getHandler(processedRequest);
         if (mappedHandler == null) {
            noHandlerFound(processedRequest, response);
            return;
         }

         // Determine handler adapter for the current request.

         // 获取处理器适配器, 根据不同种类的适配器支持程度supports方法, 获取到合适的适配器, 处理的核心方法为handle方法
         // mappedHandler.getHandler()获取的是HandlerMethod对象
         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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
               return;
            }
         }

         // 处理拦截器preHandle方法
         if (!mappedHandler.applyPreHandle(processedRequest, response)) {
            return;
         }

         // Actually invoke the handler.

         // 调用HandlerAdapter的handle方法
         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

         if (asyncManager.isConcurrentHandlingStarted()) {
            return;
         }

         // 处理视图名字
         applyDefaultViewName(processedRequest, mv);

         // 处理拦截器postHandle方法
         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);
      }

      // 处理视图渲染
      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);
         }
      }
   }
}