SpringMVC-调用原理解析

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.
        //获取真正执行的Handler
        mappedHandler = getHandler(processedRequest);
        if (mappedHandler == null) {
          noHandlerFound(processedRequest, response);
          return;
        }


        // Determine handler adapter for the current request.
        //根据handler封装Handler适配器
        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)) {
          //获取最后修改时间
          long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
          if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
            return;
          }
        }
        //拦截器前置处理
        if (!mappedHandler.applyPreHandle(processedRequest, response)) {
          return;
        }


        // Actually invoke the handler.
        //执行Handler返回ModelAndView
        mv = ha.handle(processedRequest, response, mappedHandler.getHandler());


        if (asyncManager.isConcurrentHandlingStarted()) {
          return;
        }
        //申请默认的视图名称
        applyDefaultViewName(processedRequest, mv);
        //拦截器后置处理
        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);
      }
      //处理结果-解析视图-渲染view
      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);
        }
      }
    }
  }
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