SpringMVC核心处理流程梳理

1、处理流程图展示

当我拿出这张图，阁下又该如何应对呢？执行流程是不是一目了然了。
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2、DispatcherServlet：中央处理器或者中央调度器

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下图官方的解释应该最完善了。
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3、SpringMVC三大核心组件

HandlerMapping
处理器映射器，作用是解析URL，返回执行链以及一些列所需的拦截器（DispatcherServlet源代码1030行的doDispatch(HttpServletRequest request, HttpServletResponse response)方法里面清晰地展示了执行流程，大家有兴趣了可以去看看，就是一个方法套方法的执行链条，最终将请求进行处理，直到返回ModelAndView。）

/*** Process the actual dispatching to the handler.* <p>The handler will be obtained by applying the servlet's HandlerMappings in order.* The HandlerAdapter will be obtained by querying the servlet's installed HandlerAdapters* to find the first that supports the handler class.* <p>All HTTP methods are handled by this method. It's up to HandlerAdapters or handlers* themselves to decide which methods are acceptable.* @param request current HTTP request* @param response current HTTP response* @throws Exception in case of any kind of processing failure*/@SuppressWarnings("deprecation")// 最核心的请求、响应处理方法protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception //封装好的请求实例HttpServletRequest processedRequest = request;// 处理器执行责任链HandlerExecutionChain mappedHandler = null;//是否是多媒体文件请求boolean multipartRequestParsed = false;//WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);try {ModelAndView mv = null;Exception dispatchException = null;try {processedRequest = checkMultipart(request);multipartRequestParsed = (processedRequest != request);// 传递请求，最终初始化处理器映射器mappedHandler = getHandler(processedRequest);if (mappedHandler == null) {noHandlerFound(processedRequest, response);return;}// 根据前面的处理器映射器初始化处理器适配器HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// 拿到请求方式String method = request.getMethod();//是否是GET请求boolean isGet = HttpMethod.GET.matches(method);if (isGet || HttpMethod.HEAD.matches(method)) {long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// 真正的处理请求，并返回模型和视图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);}// 封装视图结果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 afterCompletionif (mappedHandler != null) {mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}}