001 springmvc概述

protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
        HttpServletRequest processedRequest = request;  //将请求换成一个处理请求的引用
        HandlerExecutionChain mappedHandler = null;   // 定义处理器质性链
        boolean multipartRequestParsed = false;   // 是否跟文件上传有关
　　　　 //这个是异步的行为,我们这里不去关心
        WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);

        try {
            ModelAndView mv = null;   // 返回值
            Exception dispatchException = null; //异常

            try {
                processedRequest = checkMultipart(request); //检查是否含有文件上传
                multipartRequestParsed = (processedRequest != request); //如果是文件上传,进行请求的转换

                // Determine handler for the current request.
                mappedHandler = getHandler(processedRequest); //通过请求,寻找对象的处理器映射器
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);  //没有处理器映射器,就说明这个请求的地址没有注册
                    return;
                }

                // Determine handler adapter for the current request.
　　　　　　　　　　
 　　　　　　　　　//1.首先从处理器映射器之中获取处理器执行链
                // 2/ 然后将处理器执行链转换为处理器适配器

                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)) {
                    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;
                    }
                }
　　　　　　　　　　// 处理器执行链的前置拦截行为
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }
                //调用真正的处理器方法
                // Actually invoke the handler.
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
                //转换视图等行为,为域对象存放值等行为
                applyDefaultViewName(processedRequest, mv);
　　　　　　　　　　//应该处理器拦截链的后置处理行为
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
                dispatchException = ex; //如果出现异常,这个异常就有了整体处理的地方
            }
            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);
                }
            }
        }
    }