SpringMVC 源码分析之 DispatcherServlet

protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception {
 logRequest(request);
 // Keep a snapshot of the request attributes in case of an include,
 // to be able to restore the original attributes after the include.
 Map<String, Object> attributesSnapshot = null;
 if (WebUtils.isIncludeRequest(request)) {
  attributesSnapshot = new HashMap<>();
  Enumeration<?> attrNames = request.getAttributeNames();
  while (attrNames.hasMoreElements()) {
   String attrName = (String) attrNames.nextElement();
   if (this.cleanupAfterInclude || attrName.startsWith(DEFAULT_STRATEGIES_PREFIX)) {
    attributesSnapshot.put(attrName, request.getAttribute(attrName));
   }
  }
 }
 // Make framework objects available to handlers and view objects.
 request.setAttribute(WEB_APPLICATION_CONTEXT_ATTRIBUTE, getWebApplicationContext());
 request.setAttribute(LOCALE_RESOLVER_ATTRIBUTE, this.localeResolver);
 request.setAttribute(THEME_RESOLVER_ATTRIBUTE, this.themeResolver);
 request.setAttribute(THEME_SOURCE_ATTRIBUTE, getThemeSource());
 if (this.flashMapManager != null) {
  FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
  if (inputFlashMap != null) {
   request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));
  }
  request.setAttribute(OUTPUT_FLASH_MAP_ATTRIBUTE, new FlashMap());
  request.setAttribute(FLASH_MAP_MANAGER_ATTRIBUTE, this.flashMapManager);
 }
 RequestPath previousRequestPath = null;
 if (this.parseRequestPath) {
  previousRequestPath = (RequestPath) request.getAttribute(ServletRequestPathUtils.PATH_ATTRIBUTE);
  ServletRequestPathUtils.parseAndCache(request);
 }
 try {
  doDispatch(request, response);
 }
 finally {
  if (!WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
   // Restore the original attribute snapshot, in case of an include.
   if (attributesSnapshot != null) {
    restoreAttributesAfterInclude(request, attributesSnapshot);
   }
  }
  ServletRequestPathUtils.setParsedRequestPath(previousRequestPath, request);
 }
}

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 {
   processedRequest = checkMultipart(request);
   multipartRequestParsed = (processedRequest != request);
   // Determine handler for the current request.
   mappedHandler = getHandler(processedRequest);
   if (mappedHandler == null) {
    noHandlerFound(processedRequest, response);
    return;
   }
   // Determine handler adapter for the current request.
   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 (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
     return;
    }
   }
   if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    return;
   }
   // Actually invoke the handler.
   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);
  }
  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);
   }
  }
 }
}

private void processDispatchResult(HttpServletRequest request, HttpServletResponse response,
  @Nullable HandlerExecutionChain mappedHandler, @Nullable ModelAndView mv,
  @Nullable Exception exception) throws Exception {
 boolean errorView = false;
 if (exception != null) {
  if (exception instanceof ModelAndViewDefiningException) {
   mv = ((ModelAndViewDefiningException) exception).getModelAndView();
  }
  else {
   Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null);
   mv = processHandlerException(request, response, handler, exception);
   errorView = (mv != null);
  }
 }
 // Did the handler return a view to render?
 if (mv != null && !mv.wasCleared()) {
  render(mv, request, response);
  if (errorView) {
   WebUtils.clearErrorRequestAttributes(request);
  }
 }
 else {
 }
 if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {
  // Concurrent handling started during a forward
  return;
 }
 if (mappedHandler != null) {
  // Exception (if any) is already handled..
  mappedHandler.triggerAfterCompletion(request, response, null);
 }
}