spring mvc DispatcherServlet之前端控制器架构详解

 protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); //文件上传解析，如果请求类型是multipart将通过MultipartResolver进行文件上传解析； initLocaleResolver(context); //本地化解析 initThemeResolver(context);　　　//主题解析 initHandlerMappings(context); //通过HandlerMapping，将请求映射到处理器 initHandlerAdapters(context); //通过HandlerAdapter支持多种类型的处理器 initHandlerExceptionResolvers(context); //如果执行过程中遇到异常将交给HandlerExceptionResolver来解析 initRequestToViewNameTranslator(context); //直接解析请求到视图名 initViewResolvers(context); //通过ViewResolver解析逻辑视图名到具体视图实现 initFlashMapManager(context); //flash映射管理器 }

 /** * Override the parent class implementation in order to intercept PATCH * requests. */ @Override protected void service(HttpServletRequest request, HttpServletResponse response)  throws ServletException, IOException { String method = request.getMethod(); if (method.equalsIgnoreCase(RequestMethod.PATCH.name())) {  processRequest(request, response); } else {  super.service(request, response); } }

public enum RequestMethod {GET, HEAD, POST, PUT, PATCH, DELETE, OPTIONS, TRACE}

 /** * Process this request, publishing an event regardless of the outcome. * <p>The actual event handling is performed by the abstract * {@link #doService} template method. */ protected final void processRequest(HttpServletRequest request, HttpServletResponse response)  throws ServletException, IOException { long startTime = System.currentTimeMillis(); Throwable failureCause = null; LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext(); LocaleContext localeContext = buildLocaleContext(request); RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes(); ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes); WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request); asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor()); initContextHolders(request, localeContext, requestAttributes); try {  doService(request, response); } catch (ServletException ex) {  failureCause = ex;  throw ex; } catch (IOException ex) {  failureCause = ex;  throw ex; } catch (Throwable ex) {  failureCause = ex;  throw new NestedServletException("Request processing failed", ex); } finally {  resetContextHolders(request, previousLocaleContext, previousAttributes);  if (requestAttributes != null) {  requestAttributes.requestCompleted();  }  if (logger.isDebugEnabled()) {  if (failureCause != null) {   this.logger.debug("Could not complete request", failureCause);  }  else {   if (asyncManager.isConcurrentHandlingStarted()) {   logger.debug("Leaving response open for concurrent processing");   }   else {   this.logger.debug("Successfully completed request");   }  }  }  publishRequestHandledEvent(request, startTime, failureCause); } }

/** * Subclasses must implement this method to do the work of request handling, * receiving a centralized callback for GET, POST, PUT and DELETE. * <p>The contract is essentially the same as that for the commonly overridden * {@code doGet} or {@code doPost} methods of HttpServlet. * <p>This class intercepts calls to ensure that exception handling and * event publication takes place. * @param request current HTTP request * @param response current HTTP response * @throws Exception in case of any kind of processing failure * @see javax.servlet.http.HttpServlet#doGet * @see javax.servlet.http.HttpServlet#doPost */ protected abstract void doService(HttpServletRequest request, HttpServletResponse response)  throws Exception;

 /** * Exposes the DispatcherServlet-specific request attributes and delegates to {@link #doDispatch} * for the actual dispatching. */ @Override protected void doService(HttpServletRequest request, HttpServletResponse response) throws Exception { if (logger.isDebugEnabled()) {  String resumed = WebAsyncUtils.getAsyncManager(request).hasConcurrentResult() ? " resumed" : "";  logger.debug("DispatcherServlet with name '" + getServletName() + "'" + resumed +   " processing " + request.getMethod() + " request for [" + getRequestUri(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<String, Object>();  Enumeration<?> attrNames = request.getAttributeNames();  while (attrNames.hasMoreElements()) {  String attrName = (String) attrNames.nextElement();  if (this.cleanupAfterInclude || attrName.startsWith("org.springframework.web.servlet")) {   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()); 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); try {  doDispatch(request, response); } finally {  if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) {  return;  }  // Restore the original attribute snapshot, in case of an include.  if (attributesSnapshot != null) {  restoreAttributesAfterInclude(request, attributesSnapshot);  } } }

 /** * 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 */ 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 || mappedHandler.getHandler() == 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 (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;  }  try {   // Actually invoke the handler.   mv = ha.handle(processedRequest, response, mappedHandler.getHandler());  }  finally {   if (asyncManager.isConcurrentHandlingStarted()) {   return;   }  }  applyDefaultViewName(request, mv);  mappedHandler.applyPostHandle(processedRequest, response, mv);  }  catch (Exception ex) {  dispatchException = ex;  }  processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); } catch (Exception ex) {  triggerAfterCompletion(processedRequest, response, mappedHandler, ex); } catch (Error err) {  triggerAfterCompletionWithError(processedRequest, response, mappedHandler, err); } finally {  if (asyncManager.isConcurrentHandlingStarted()) {  // Instead of postHandle and afterCompletion  mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);  return;  }  // Clean up any resources used by a multipart request.  if (multipartRequestParsed) {  cleanupMultipart(processedRequest);  } } }

 /** * Close the WebApplicationContext of this servlet. * @see org.springframework.context.ConfigurableApplicationContext#close() */ @Override public void destroy() { getServletContext().log("Destroying Spring FrameworkServlet '" + getServletName() + "'"); // Only call close() on WebApplicationContext if locally managed... if (this.webApplicationContext instanceof ConfigurableApplicationContext && !this.webApplicationContextInjected) {  ((ConfigurableApplicationContext) this.webApplicationContext).close(); } }