SpringMVC学习——概念、流程图、源码简析（一）

　　学习资料：开涛的《跟我学SpringMVC.pdf》

　　众所周知，springMVC是比较常用的web框架，通常整合spring使用。这里抛开spring，单纯的对springMVC做一下总结。

　　概念

　　HandlerMapping：处理器映射，对请求的URL进行映射为具体的处理器（如果有拦截器也包含拦截器，会将Handler和多个HandlerInterceptor封装为HandlerExecutionChain对象）

　　HandlerAdapter：处理器适配器，适配不同类型的处理器，如Controller、AbstractController等

　　Handler：处理器，即开发的Controller

　　ModeAndView：模型和视图，未来会渲染为具体的视图

　　ViewResolver：视图解析器，将逻辑视图名称转化为物理视图

　　View：视图

　　流程图

　　源码简析（摘自DispatcherServlet源码部分）

　　由于springMVC的配置本身就上一个servlet，所以跟踪代码doService()=>doDispatcher()，核心代码如下所示，中文注释自己加的：

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 {
                //对文件上传类型的数据进行处理，使用MultipartResolver解析
                processedRequest = checkMultipart(request);
                multipartRequestParsed = (processedRequest != request);

                //使用HandlerMapping进行映射，将一个Handler和多个HandlerInterceptor封装为HandlerExecutionChain对象
                mappedHandler = getHandler(processedRequest);
                if (mappedHandler == null || mappedHandler.getHandler() == null) {
                    noHandlerFound(processedRequest, response);
                    return;
                }

                //根据Handler获取合适的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)) {
                    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;
                    }
                }

                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }

                //使用HandlerAdapter执行Handler并返回ModeAndView
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

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

                applyDefaultViewName(processedRequest, mv);
                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);
            }
            //处理转发结果，包含ModeAndView的视图解析
            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);
                }
            }
        }
    }