代码分析Spring MVC的工作原理

static {
 // Load default strategy implementations from properties file.
 // This is currently strictly internal and not meant to be customized
 // by application developers.
 try {
  ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
  defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
 }
 catch (IOException ex) {
  throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
 }
 }

# Default implementation classes for DispatcherServlet's strategy interfaces.
# Used as fallback when no matching beans are found in the DispatcherServlet context.
# Not meant to be customized by application developers.

org.springframework.web.servlet.LocaleResolver=org.springframework.web.servlet.i18n.AcceptHeaderLocaleResolver

org.springframework.web.servlet.ThemeResolver=org.springframework.web.servlet.theme.FixedThemeResolver

org.springframework.web.servlet.HandlerMapping=org.springframework.web.servlet.handler.BeanNameUrlHandlerMapping,\
 org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping

org.springframework.web.servlet.HandlerAdapter=org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter,\
 org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter,\
 org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter

org.springframework.web.servlet.HandlerExceptionResolver=org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerExceptionResolver,\
 org.springframework.web.servlet.mvc.annotation.ResponseStatusExceptionResolver,\
 org.springframework.web.servlet.mvc.support.DefaultHandlerExceptionResolver

org.springframework.web.servlet.RequestToViewNameTranslator=org.springframework.web.servlet.view.DefaultRequestToViewNameTranslator

org.springframework.web.servlet.ViewResolver=org.springframework.web.servlet.view.InternalResourceViewResolver

org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager

protected void initStrategies(ApplicationContext context) {
 initMultipartResolver(context);
 initLocaleResolver(context);
 initThemeResolver(context);
 initHandlerMappings(context);
 initHandlerAdapters(context);
 initHandlerExceptionResolvers(context);
 initRequestToViewNameTranslator(context);
 initViewResolvers(context);
 initFlashMapManager(context);
}

@Override
protected void initApplicationContext() throws BeansException {
 extendInterceptors(this.interceptors);
 detectMappedInterceptors(this.mappedInterceptors);
 initInterceptors();
}

/**
 * Process the actual dispatching to the handler. 将请求分发到具体的handler，也就是我们的controller
 * <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. 决定哪个handler来处理当前的请求
   // mappedHandler是由handler和interceptor集合组成的一个执行链，有点类似FilterChain
   mappedHandler = getHandler(processedRequest);
   if (mappedHandler == null || mappedHandler.getHandler() == null) {
    noHandlerFound(processedRequest, response);
    return;
   }

   // Determine handler adapter for the current request. 决定哪个adapter来处理当前的请求
   // handlerMapping是找出适配的handler，而真正回调handler的是adapter
   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()) {
     String requestUri = urlPathHelper.getRequestUri(request);
     logger.debug("Last-Modified value for [" + requestUri + "] is: " + lastModified);
    }
    if (new ServletWebRequest(request, response).checkNotModified(lastModified) && isGet) {
     return;
    }
   }

   // handler的前置处理，也就是调用适配当前url的interceptor的preHandler方法
   if (!mappedHandler.applyPreHandle(processedRequest, response)) {
    return;
   }

   try {
    // Actually invoke the handler. 真正调用handler
    mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
   }
   finally {
    if (asyncManager.isConcurrentHandlingStarted()) {
     return;
    }
   }

   applyDefaultViewName(request, mv);
   // handler的后置处理，也就是调用适配当前url的interceptor的postHandler方法
   mappedHandler.applyPostHandle(processedRequest, response, mv);
  }
  catch (Exception ex) {
   dispatchException = ex;
  }
  // 处理handler返回的结果，会调用适配当前url的interceptor的afterCompletion方法
  // 这里会将响应结果返回给请求者
  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);
  }
 }
}