DispatcherServlet接收请求

1：DispatcherServlet 是 SpringMVC 中的前端控制器(Front Controller),负责接收 Request并将 Request 转发给对应的处理组件.
2：HanlerMapping 是 SpringMVC 中完成 url 到 Controller 映射的组件.DispatcherServlet接收 Request,然后从 HandlerMapping 查找处理 Request 的 Controller.
3：Cntroller 处理 Request,并返回 ModelAndView 对象,Controller 是 SpringMVC 中负责处理 Request 的组件(类似于 Struts2 中的 Action),ModelAndView 是封装结果视图的组件.

4 5 6：视图解析器解析 ModelAndView 对象并返回对应的视图给客户端。 

1.根据访问 url 找到对应的 Controller 中处理请求的方法

入口为 DispatcherServlet 的核心方法为doService(),doService()中的核心逻辑由doDispatch()实现,我们查看doDispatch()的源代码。

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 {
         //请求类型处理
         processedRequest = checkMultipart(request);
         multipartRequestParsed = (processedRequest != request);

         // 根据请求获取能够处理该请求的HandlerExecutionChain
         mappedHandler = getHandler(processedRequest);
         if (mappedHandler == null) {
            noHandlerFound(processedRequest, response);
            return;
         }

         // 获取请求对应的处理器适配器
         HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

         // 处理 last-modified 请求头
         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;
         }

         // 实际的处理器处理请求,返回结果视图对象
         mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

         if (asyncManager.isConcurrentHandlingStarted()) {
            return;
         }
         // 结果视图对象的处理
         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);
      }
      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) {
            // 请求成功响应之后的方法
            mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
         }
      } else {
         // Clean up any resources used by a multipart request.
         if (multipartRequestParsed) {
            cleanupMultipart(processedRequest);
         }
      }
   }
}

getHandler(processedRequest)方法实际上就是从HandlerMapping中找到url和Controller的对应关系，源码最终在AbstractHandlerMapping#getHandler方法中处理：

@Override
@Nullable
public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
   //根据request获取对应的handler--》AbstractUrlHandlerMapping
   Object handler = getHandlerInternal(request);
   if (handler == null) {
      //如果没有则使用默认的handler
      handler = getDefaultHandler();
   }
   if (handler == null) {
      return null;
   }
   // Bean name or resolved handler?
   if (handler instanceof String) {
      String handlerName = (String) handler;
      handler = obtainApplicationContext().getBean(handlerName);
   }
   //aop 加入拦截器到执行链
   HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
   if (CorsUtils.isCorsRequest(request)) {
      CorsConfiguration globalConfig = this.globalCorsConfigSource.getCorsConfiguration(request);
      CorsConfiguration handlerConfig = getCorsConfiguration(handler, request);
      CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig);
      executionChain = getCorsHandlerExecutionChain(request, executionChain, config);
   }
   return executionChain;
}

通过调用DispatcherServlet#doDispatch调用ha.handle，由RequestMappingHandlerAdapter#invokeHandlerMethod实现

protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
      HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

   ServletWebRequest webRequest = new ServletWebRequest(request, response);
   try {
      WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
      ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);

      ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
      if (this.argumentResolvers != null) {
         invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
      }
      if (this.returnValueHandlers != null) {
         invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
      }
      invocableMethod.setDataBinderFactory(binderFactory);
      invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);

      ModelAndViewContainer mavContainer = new ModelAndViewContainer();
      mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
      modelFactory.initModel(webRequest, mavContainer, invocableMethod);
      mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

      AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
      asyncWebRequest.setTimeout(this.asyncRequestTimeout);

      WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
      asyncManager.setTaskExecutor(this.taskExecutor);
      asyncManager.setAsyncWebRequest(asyncWebRequest);
      asyncManager.registerCallableInterceptors(this.callableInterceptors);
      asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

      if (asyncManager.hasConcurrentResult()) {
         Object result = asyncManager.getConcurrentResult();
         mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
         asyncManager.clearConcurrentResult();
         if (logger.isDebugEnabled()) {
            logger.debug("Found concurrent result value [" + result + "]");
         }
         invocableMethod = invocableMethod.wrapConcurrentResult(result);
      }

      invocableMethod.invokeAndHandle(webRequest, mavContainer);
      if (asyncManager.isConcurrentHandlingStarted()) {
         return null;
      }

      return getModelAndView(mavContainer, modelFactory, webRequest);
   }
   finally {
      webRequest.requestCompleted();
   }
}

上一篇: url 和 Controller 的对应关系

下一篇: Spring AOP 解析