SpringMVC学习（一）——概念、流程图、源码简析

　　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;
                        }
                    }

                    /*
                     * 调用拦截器的preHandle()，返回true继续执行下一个拦截器或处理器，返回false中断流程并执行执行成功的拦截器的afterCompletion()。
    　　　　　　　　　               */
                    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);
                    //调用拦截器的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);
                }
                //处理转发结果，包含ModeAndView的视图解析，视图解析后调用拦截器的afterCompletion()函数
                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);
                    }
                }
            }
        }