springmvcDispatcherServlet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.
 * 
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.
 * 
The contract is essentially the same as that for the commonly overridden
 * {@code doGet} or {@code doPost} methods of HttpServlet.
 * 
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 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("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.
 * 
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.
 * 
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();
 }
 }