前端请求过来先进入servlet 的 service 方法
// FrameWorkServlet @Override protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpMethod httpMethod = HttpMethod.resolve(request.getMethod()); if (httpMethod == HttpMethod.PATCH || httpMethod == null) { //<1> processRequest(request, response); } else {//<2> super.service(request, response); } }无论是<1>还是<2> 都会进入FrameWorkServlet.processRequest方法
// FrameWorkServlet 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);//进入DispatcherServlet的doservice方法 } catch (ServletException | 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(); } logResult(request, response, failureCause, asyncManager); publishRequestHandledEvent(request, response, startTime, failureCause); } }再进入DispatcherServlet的doservice方法
再进入DispatcherServlet 的 doDispatch方法 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. // 获得处理器 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; } } // 拦截器前置处理 if (!mappedHandler.applyPreHandle(processedRequest, response)) { return; } // Actually invoke the handler. // 调用请求方法 mv = ha.handle(processedRequest, response, mappedHandler.getHandler()); if (asyncManager.isConcurrentHandlingStarted()) { return; } applyDefaultViewName(processedRequest, mv); // 拦截器后置处理 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); } } } }先通过getHandler 获得 HandlerExecutionChain，调用 HandlerExecutionChain 的 applyPreHandle执行前置处理，调用 applyPostHandle 执行后置处理，至此可以看到拦截器的处理请求，拦截器处理前置请求方法如下：
boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception { HandlerInterceptor[] interceptors = getInterceptors(); if (!ObjectUtils.isEmpty(interceptors)) { for (int i = 0; i < interceptors.length; i++) { HandlerInterceptor interceptor = interceptors[i]; if (!interceptor.preHandle(request, response, this.handler)) { triggerAfterCompletion(request, response, null); return false; } this.interceptorIndex = i; } } return true; }可以看到拦截器们实际上设置在HandlerExecutionChain .interceptors属性中，那么HandlerExecutionChain .interceptors是在哪里设置的呢？往下看
// AbstractHandlerMapping public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { Object handler = getHandlerInternal(request); if (handler == null) { handler = getDefaultHandler(); } if (handler == null) { return null; } // Bean name or resolved handler? if (handler instanceof String) { String handlerName = (String) handler; handler = obtainApplicationContext().getBean(handlerName); } HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request); if (logger.isTraceEnabled()) { logger.trace("Mapped to " + handler); } else if (logger.isDebugEnabled() && !request.getDispatcherType().equals(DispatcherType.ASYNC)) { logger.debug("Mapped to " + executionChain.getHandler()); } if (CorsUtils.isCorsRequest(request)) { CorsConfiguration globalConfig = this.corsConfigurationSource.getCorsConfiguration(request); CorsConfiguration handlerConfig = getCorsConfiguration(handler, request); CorsConfiguration config = (globalConfig != null ? globalConfig.combine(handlerConfig) : handlerConfig); executionChain = getCorsHandlerExecutionChain(request, executionChain, config); } return executionChain; } // AbstractHandlerMapping protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) { HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ? (HandlerExecutionChain) handler : new HandlerExecutionChain(handler)); String lookupPath = this.urlPathHelper.getLookupPathForRequest(request); for (HandlerInterceptor interceptor : this.adaptedInterceptors) { // 如果是 MappedInterceptor 类型的拦截器 if (interceptor instanceof MappedInterceptor) { MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor; // 只有路径匹配的请求，才添加到拦截器链中 if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) { chain.addInterceptor(mappedInterceptor.getInterceptor()); } }// 不是 MappedInterceptor 类型的拦截器，直接添加到拦截器链中 else { chain.addInterceptor(interceptor); } } return chain; }回到AbstractHandlerMapping 的 getHandler方法，通过getHandlerExecutionChain创建 HandlerExecutionChain对象，HandlerExecutionChain 中 的 拦截器就是通过AbstractHandlerMapping 的 adaptedInterceptors 过滤得到。而AbstractHandlerMapping.adaptedInterceptors是在哪里初始化的呢，看下面：
AbstractHandlerMapping 实现了 ApplicationContextAware 接口，而 spring 中实现 Aware 接口的类一般在它创建完成后的初始化方法中会进行设置属性，此过程大致如下： AbstractBeanFactory.doGetBean ->AbstractAutowireCapableBeanFactory.doCreateBean ->AbstractAutowireCapableBeanFactory.initializeBean ->AbstractAutowireCapableBeanFactory.applyBeanPostProcessorsBeforeInitialization ->ApplicationContextAwareProcessor.invokeAwareInterfaces ->ApplicationObjectSupport.setApplicationContext ->WebApplicationObjectSupport.initApplicationContext ->ApplicationObjectSupport.initApplicationContext ->AbstractHandlerMapping.initApplicationContext ->AbstractHandlerMapping.detectMappedInterceptors
protected void detectMappedInterceptors(List<HandlerInterceptor> mappedInterceptors) { // 获取 spring 容器中 所有类型为 MappedInterceptor 的对象 mappedInterceptors.addAll( BeanFactoryUtils.beansOfTypeIncludingAncestors( obtainApplicationContext(), MappedInterceptor.class, true, false).values()); }至此，也知道AbstractHandlerMapping 的 adaptedInterceptors是怎么初始化的了。 整个流程大概就是spring容器初始化的时候，把所有拦截器填充到了AbstractHandlerMapping.adaptedInterceptors属性中缓存起来，等请求来了的时候通过getHandlerExecutionChain将符合条件的拦截器存到HandlerExecutionChain对象里，然后调用拦截器的前置以及后置处理方法
