`
@SuppressWarnings("deprecation")
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
// 实际处理时用的请求，如果不是上传请求，则直接使用接收到的 request,否则封装成上传的 request
HttpServletRequest processedRequest = request;
// 处理请求的处理器链(包括处理器和对应的 interceptor)
HandlerExecutionChain mappedHandler = null;
// 上传标志
boolean multipartRequestParsed = false;
// 获取异步处理器WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);try {ModelAndView mv = null;Exception dispatchException = null;try {// 检查是否是上传请求// 如果是上传请求，则将其封装成 multipartRequestParsed// 内有九个组件之一 MultipartResolverprocessedRequest = checkMultipart(request);// 上传请求标志位// 通过对象是否更改过进行判断multipartRequestParsed = (processedRequest != request);// Determine handler for the current request.// 获得请求对应的 HandlerExecutionChain 对象(HandlerMethod（Controller 的具体方法） 和 HandlerInterceptor 拦截器们)// 重要 拦截器链// 循环遍历三个 HandlerMapping 进行匹配mappedHandler = getHandler(processedRequest);// 获取不到控制器if (mappedHandler == null) {noHandlerFound(processedRequest, response);return;}// Determine handler adapter for the current request.// 通过适配器的方式进行调用，因为有多个选择。// 根据// 获取与当前 handler 匹配的 Adapter// 重要HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());// Process last-modified header, if supported by the handler.// 处理GET、HEAD请求的Last-Modified,当浏览器第一次跟服务器请求资源时，服务器会在返回的请求头里包含一个 last_modified 的属性,// last_modified 代表资源最后时什么时候修改的，在浏览器以后发送请求的时候，会同时发送之前接收到的 Last_modified .服务器接收到带last_modified的请求后，// 会跟实际资源的最后修改时间做对比，如果过期了返回新的资源，否则直接返回304表示未过期，直接使用之前缓存的结果即可// 获取请求方式String method = request.getMethod();boolean isGet = HttpMethod.GET.matches(method);if (isGet || HttpMethod.HEAD.matches(method)) {// 为了减少资源重复获取long lastModified = ha.getLastModified(request, mappedHandler.getHandler());if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {return;}}// 执行响应的 Interceptor 的 PreHandle// 注意：该方法如果有一个拦截器的前置处理器返回 false,则开始倒序触发所有的拦截器的已完成处理// mappedHandler 是 HandlerExecutionChain// 重要if (!mappedHandler.applyPreHandle(processedRequest, response)) {return;}// Actually invoke the handler.// mv ModelAndView// 使用适配器执行 handler，并返回视图// 重要// AbstractHandlerMethodAdaptermv = ha.handle(processedRequest, response, mappedHandler.getHandler());// 如果有异步处理if (asyncManager.isConcurrentHandlingStarted()) {return;}// 如果 view 为空，根据 request 设置默认的 view// 默认名字为 请求路径名。// 组件：RequestToViewNameTranslatorapplyDefaultViewName(processedRequest, mv);// 重要 拦截器的后置处理器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 ServletException("Handler dispatch failed: " + err, err);}// 重要// 处理返回结果，包括处理异常，页面渲染processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);}catch (Exception ex) {triggerAfterCompletion(processedRequest, response, mappedHandler, ex);}catch (Throwable err) {triggerAfterCompletion(processedRequest, response, mappedHandler,new ServletException("Handler processing failed: " + err, err));}finally {if (asyncManager.isConcurrentHandlingStarted()) {// Instead of postHandle and afterCompletionif (mappedHandler != null) {// 触发 Interceptor 的 afterCompletionmappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);}}else {// Clean up any resources used by a multipart request.if (multipartRequestParsed) {cleanupMultipart(processedRequest);}}}
}`
1.getHandel()
@Nullable protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { if (this.handlerMappings != null) { // 默认有三个 for (HandlerMapping mapping : this.handlerMappings) { // BeanNameUrlHandlerMapping 第一次 匹配不到 // RequestMappingHandlerMapping - 第二个 通过@Controller生成的 HandlerExecutionChain handler = mapping.getHandler(request); if (handler != null) { return handler; } } } return null; }
通过断点可以看到默认会有两个HandlerMapping的实现：RequestMappingHandlerMapping和BeanNameUrlHandlerMapping；
所有加了@Controller的Controller对象会放在RequestMappingHandlerMapping的父类
HandlerExecutionChain即为控制器与连接器
2.由于SpringMVC提供了4种类型的HandlerAdapter，并且他们没有统一的调用接口，所以需要通过适配器来使用。同样适配器的类型也有4种。如下所示：
protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException { if (this.handlerAdapters != null) { for (HandlerAdapter adapter : this.handlerAdapters) { if (adapter.supports(handler)) { return adapter; } } } throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler"); }
支持当前Handler类型的适配器并返回
3.执行 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());,
4.执行响应的interceptor的postHandler方法
查找视图，并相应View
