/**
* 建立當前ApplicationContext中的所有controller和url的對應關系
*/
protected void detectHandlers() throws BeansException {
  //日志級別是否是 Debug
  if (logger.isDebugEnabled()) {
    //應用上下文就是工程的訪問路徑
    logger.debug("Looking for URL mappings in application context: " + getApplicationContext());
  }
　　　　 // 獲取ApplicationContext容器中所有bean的Name---Controller
  String[] beanNames = (this.detectHandlersInAncestorContexts ?
      BeanFactoryUtils.beanNamesForTypeIncludingAncestors(getApplicationContext(), Object.class) :
      getApplicationContext().getBeanNamesForType(Object.class));

  // 遍歷beanNames,并找到這些bean對應的url
  for (String beanName : beanNames) {
　　　　　　 // 獲取Controller上的所有url(類上的url+方法上的url)
    String[] urls = determineUrlsForHandler(beanName);
    if (!ObjectUtils.isEmpty(urls)) {
      // 保存urls和beanName的對應關系,put it to Map<urls,beanName>,該方法在父類AbstractUrlHandlerMapping中實現(xiàn)
      registerHandler(urls, beanName);
    }
    else {
      if (logger.isDebugEnabled()) {
        logger.debug("Rejected bean name '" + beanName + "': no URL paths identified");
      }
    }
  }
}

/** 中央控制器,控制請求的轉發(fā) **/
protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
HttpServletRequest processedRequest = request;
HandlerExecutionChain mappedHandler = null;
int interceptorIndex = -1;

try {
  ModelAndView mv;
  boolean errorView = false;
  try {
　　　　// 1.檢查是否是文件上傳的請求
    processedRequest = checkMultipart(request);

    // 2.取得處理當前請求的controller,這里也稱為hanlder,處理器,第一個步驟的意義就在這里體現(xiàn)了.
    這里并不是直接返回controller,而是返回的HandlerExecutionChain請求處理器鏈對象，該對象封裝了handler和interceptors.
    mappedHandler = getHandler(processedRequest, false);
　　　　// 如果handler為空,則返回404
    if (mappedHandler == null || mappedHandler.getHandler() == null) {
      noHandlerFound(processedRequest, response);
      return;
    }
    //3. 獲取處理request的處理器適配器handler adapter 
    HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
    // 處理 last-modified 請求頭
    String method = request.getMethod();
    boolean isGet = "GET".equals(method);
    if (isGet || "HEAD".equals(method)) {
      long lastModified = ha.getLastModified(request, mappedHandler.getHandler());
      if (logger.isDebugEnabled()) {
        String requestUri = urlPathHelper.getRequestUri(request);
        logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
      }
      if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
        return;
      }
    }

    // 4.攔截器的預處理方法
    HandlerInterceptor[] interceptors = mappedHandler.getInterceptors();
    if (interceptors != null) {
      for (int i = 0; i < interceptors.length; i++) {
        HandlerInterceptor interceptor = interceptors[i];
        if (!interceptor.preHandle(processedRequest, response, mappedHandler.getHandler())) {
          triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
          return;
        }
        interceptorIndex = i;
      }
    }

    // 5.實際的處理器處理請求,返回結果視圖對象
    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

    // 結果視圖對象的處理
    if (mv != null && !mv.hasView()) {
      mv.setViewName(getDefaultViewName(request));
    }

    // 6.攔截器的后處理方法
    if (interceptors != null) {
      for (int i = interceptors.length - 1; i >= 0; i--) {
        HandlerInterceptor interceptor = interceptors[i];
        interceptor.postHandle(processedRequest, response, mappedHandler.getHandler(), mv);
      }
    }
  }
  catch (ModelAndViewDefiningException ex) {
    logger.debug("ModelAndViewDefiningException encountered", ex);
    mv = ex.getModelAndView();
  }
  catch (Exception ex) {
    Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
    mv = processHandlerException(processedRequest, response, handler, ex);
    errorView = (mv != null);
  }

  
  if (mv != null && !mv.wasCleared()) {
    render(mv, processedRequest, response);
    if (errorView) {
      WebUtils.clearErrorRequestAttributes(request);
    }
  }
  else {
    if (logger.isDebugEnabled()) {
      logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() +
          "': assuming HandlerAdapter completed request handling");
    }
  }

  // 請求成功響應之后的方法
  triggerAfterCompletion(mappedHandler, interceptorIndex, processedRequest, response, null);
}

/** 獲取處理請求的方法,執(zhí)行并返回結果視圖 **/
protected ModelAndView invokeHandlerMethod(HttpServletRequest request, HttpServletResponse response, Object handler)
	throws Exception {
　 // 1.獲取方法解析器
  ServletHandlerMethodResolver methodResolver = getMethodResolver(handler);　　　　 
  // 2.解析request中的url,獲取處理request的方法 
  //通過 request 找 controller 中的處理方法，request的url與 controller 的url 進行匹配
  Method handlerMethod = methodResolver.resolveHandlerMethod(request);　　　　 
  // 3.方法調用器
  ServletHandlerMethodInvoker methodInvoker = new ServletHandlerMethodInvoker(methodResolver);
  ServletWebRequest webRequest = new ServletWebRequest(request, response);
  ExtendedModelMap implicitModel = new BindingAwareModelMap();
　　　　 // 4.執(zhí)行方法
  Object result = methodInvoker.invokeHandlerMethod(handlerMethod, handler, webRequest, implicitModel);　　　　 
  // 5.封裝結果視圖
  ModelAndView mav =
      methodInvoker.getModelAndView(handlerMethod, handler.getClass(), result, implicitModel, webRequest);
  methodInvoker.updateModelAttributes(handler, (mav != null ? mav.getModel() : null), implicitModel, webRequest);
  return mav;
}