/**
     * Called by the servlet container to allow the servlet to respond to a request.
     *
     * <p>
     * This method is only called after the servlet's <code>init()</code> method has completed successfully.
     * 
     * <p>
     * The status code of the response always should be set for a servlet that throws or sends an error.
     *
     * 
     * <p>
     * Servlets typically run inside multithreaded servlet containers that can handle multiple requests concurrently.
     * Developers must be aware to synchronize access to any shared resources such as files, network connections, and as
     * well as the servlet's class and instance variables.
     *
     * @param req the <code>ServletRequest</code> object that contains the client's request
     *
     * @param res the <code>ServletResponse</code> object that contains the servlet's response
     *
     * @exception ServletException if an exception occurs that interferes with the servlet's normal operation
     *
     * @exception IOException if an input or output exception occurs
     *
     */
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException;

/**
     * Dispatches client requests to the protected <code>service</code> method. There's no need to override this method.
     * 
     * @param req the {@link HttpServletRequest} object that contains the request the client made of the servlet
     *
     * @param res the {@link HttpServletResponse} object that contains the response the servlet returns to the client
     *
     * @throws IOException if an input or output error occurs while the servlet is handling the HTTP request
     *
     * @throws ServletException if the HTTP request cannot be handled or if either parameter is not an instance of its
     * respective {@link HttpServletRequest} or {@link HttpServletResponse} counterparts.
     * 
     * @see jakarta.servlet.Servlet#service
     */
    @Override
    public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException {
        HttpServletRequest request;
        HttpServletResponse response;

        if (!(req instanceof HttpServletRequest && res instanceof HttpServletResponse)) {
            throw new ServletException("non-HTTP request or response");
        }

        request = (HttpServletRequest) req;
        response = (HttpServletResponse) res;

        service(request, response);
    }
}

  protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        String method = req.getMethod();

        if (method.equals(METHOD_GET)) {
            long lastModified = getLastModified(req);
            if (lastModified == -1) {
                // servlet doesn't support if-modified-since, no reason
                // to go through further expensive logic
                doGet(req, resp);
            } else {
                long ifModifiedSince = req.getDateHeader(HEADER_IFMODSINCE);
                if (ifModifiedSince < lastModified) {
                    // If the servlet mod time is later, call doGet()
                    // Round down to the nearest second for a proper compare
                    // A ifModifiedSince of -1 will always be less
                    maybeSetLastModified(resp, lastModified);
                    doGet(req, resp);
                } else {
                    resp.setStatus(HttpServletResponse.SC_NOT_MODIFIED);
                }
            }

        } else if (method.equals(METHOD_HEAD)) {
            long lastModified = getLastModified(req);
            maybeSetLastModified(resp, lastModified);
            doHead(req, resp);

        } else if (method.equals(METHOD_POST)) {
            doPost(req, resp);

        } else if (method.equals(METHOD_PUT)) {
            doPut(req, resp);

        } else if (method.equals(METHOD_DELETE)) {
            doDelete(req, resp);

        } else if (method.equals(METHOD_OPTIONS)) {
            doOptions(req, resp);

        } else if (method.equals(METHOD_TRACE)) {
            doTrace(req, resp);

        } else {
            //
            // Note that this means NO servlet supports whatever
            // method was requested, anywhere on this server.
            //

            String errMsg = lStrings.getString("http.method_not_implemented");
            Object[] errArgs = new Object[1];
            errArgs[0] = method;
            errMsg = MessageFormat.format(errMsg, errArgs);

            resp.sendError(HttpServletResponse.SC_NOT_IMPLEMENTED, errMsg);
        }
    }

	/**
	 * Delegate POST requests to {@link #processRequest}.
	 * @see #doService
	 */
	@Override
	protected final void doPost(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		processRequest(request, response);
	}

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		long startTime = System.currentTimeMillis();
		Throwable failureCause = null;
            //获得之前请求的LocaleContext
		LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
		LocaleContext localeContext = buildLocaleContext(request);
            //获得之前请求的参数
		RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
		ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
            //初始化ContextHolders
		initContextHolders(request, localeContext, requestAttributes);

		try {
            //处理请求的方法
			doService(request, response);
		}
		catch (ServletException | IOException ex) {
			failureCause = ex;
			throw ex;
		}
		catch (Throwable ex) {
			failureCause = ex;
			throw new ServletException("Request processing failed: " + ex, ex);
		}

		finally {
            //重置ContextHolders
			resetContextHolders(request, previousLocaleContext, previousAttributes);
			if (requestAttributes != null) {
				requestAttributes.requestCompleted();
			}
            //纪录日志和发布事件
			logResult(request, response, failureCause, asyncManager);
			publishRequestHandledEvent(request, response, startTime, failureCause);
		}
	}

@Override
	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.
                 //将WebApplicationContext、localeResolver、themeResolver等资源的引用存入reques的参数内
		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 {
                    //真正的处理请求方法
			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);
				}
			}
			if (this.parseRequestPath) {
				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.
                             //请求HandlerMapping获得HandlerExecutionChain(handler+interceptorList)
				mappedHandler = getHandler(processedRequest);
				if (mappedHandler == null) {
					noHandlerFound(processedRequest, response);
					return;
				}

				// Determine handler adapter for the current request.
                            //获得handler的适配器HandlerAdapter
				HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

				// Process last-modified header, if supported by the handler.
				String method = request.getMethod();
				boolean isGet = HttpMethod.GET.matches(method);
				if (isGet || HttpMethod.HEAD.matches(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handler(controller)的目标方法
				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 ServletException("Handler dispatch failed: " + err, err);
			}
                            //处理handler(controller)的目标方法的返回结果
                            //1.异常处理processHandlerException
                            //2.视图解析resolveViewName
                            //3.视图渲染view.render()
			processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
		}
		catch (Exception ex) {
                         //拦截器最终处理
			triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
		}
		catch (Throwable err) {
			triggerAfterCompletion(processedRequest, response, mappedHandler,
					new ServletException("Handler processing failed: " + err, 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);
				}
			}
		}
	}

@Nullable
	protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		if (this.handlerMappings != null) {
			for (HandlerMapping mapping : this.handlerMappings) {
				HandlerExecutionChain handler = mapping.getHandler(request);
				if (handler != null) {
					return handler;
				}
			}
		}
		return null;
	}

	@Override
	@Nullable
	public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
		//获得handler
		Object handler = getHandlerInternal(request);
		if (handler == null) {
			handler = getDefaultHandler();
		}
		if (handler == null) {
			return null;
		}
		// Bean name or resolved handler?
		if (handler instanceof String handlerName) {
			handler = obtainApplicationContext().getBean(handlerName);
		}
		//获得拦截器列表
		HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);

		return executionChain;
	}

	// Handler method lookup

/**
 * Look up a handler method for the given request.
 */
@Override
@Nullable
protected HandlerMethod getHandlerInternal(HttpServletRequest request) throws Exception {
        String lookupPath = initLookupPath(request);
        this.mappingRegistry.acquireReadLock();
        try {
        HandlerMethod handlerMethod = lookupHandlerMethod(lookupPath, request);
        return (handlerMethod != null ? handlerMethod.createWithResolvedBean() : null);
        }
        finally {
        this.mappingRegistry.releaseReadLock();
        }
        }

@Nullable
	protected HandlerMethod lookupHandlerMethod(String lookupPath, HttpServletRequest request) throws Exception {
		List<Match> matches = new ArrayList<>();
		List<T> directPathMatches = this.mappingRegistry.getMappingsByDirectPath(lookupPath);
		if (directPathMatches != null) {
			addMatchingMappings(directPathMatches, matches, request);
		}
		if (matches.isEmpty()) {
			addMatchingMappings(this.mappingRegistry.getRegistrations().keySet(), matches, request);
		}
		if (!matches.isEmpty()) {
			Match bestMatch = matches.get(0);
			if (matches.size() > 1) {
				Comparator<Match> comparator = new MatchComparator(getMappingComparator(request));
				matches.sort(comparator);
				bestMatch = matches.get(0);
				if (logger.isTraceEnabled()) {
					logger.trace(matches.size() + " matching mappings: " + matches);
				}
				if (CorsUtils.isPreFlightRequest(request)) {
					for (Match match : matches) {
						if (match.hasCorsConfig()) {
							return PREFLIGHT_AMBIGUOUS_MATCH;
						}
					}
				}
				else {
					Match secondBestMatch = matches.get(1);
					if (comparator.compare(bestMatch, secondBestMatch) == 0) {
						Method m1 = bestMatch.getHandlerMethod().getMethod();
						Method m2 = secondBestMatch.getHandlerMethod().getMethod();
						String uri = request.getRequestURI();
						throw new IllegalStateException(
								"Ambiguous handler methods mapped for '" + uri + "': {" + m1 + ", " + m2 + "}");
					}
				}
			}
            //匹配到最合适的HandlerMethod
			request.setAttribute(BEST_MATCHING_HANDLER_ATTRIBUTE, bestMatch.getHandlerMethod());
			handleMatch(bestMatch.mapping, lookupPath, request);
			return bestMatch.getHandlerMethod();
		}
		else {
			return handleNoMatch(this.mappingRegistry.getRegistrations().keySet(), lookupPath, request);
		}
	}

protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException {
		if (this.handlerAdapters != null) {
			for (HandlerAdapter adapter : this.handlerAdapters) {
				if (adapter.supports(handler)) {
					return adapter;
				}
			}
		}
		throw new ServletException("No adapter for handler [" + handler +
				"]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler");
	}

/**
 * This implementation expects the handler to be an {@link HandlerMethod}.
 * @param handler the handler instance to check
 * @return whether this adapter can adapt the given handler
 */
@Override
public final boolean supports(Object handler) {
        return (handler instanceof HandlerMethod handlerMethod && supportsInternal(handlerMethod));
        }

	/**
	 * Always return {@code true} since any method argument and return value
	 * type will be processed in some way. A method argument not recognized
	 * by any HandlerMethodArgumentResolver is interpreted as a request parameter
	 * if it is a simple type, or as a model attribute otherwise. A return value
	 * not recognized by any HandlerMethodReturnValueHandler will be interpreted
	 * as a model attribute.
	 */
	@Override
	protected boolean supportsInternal(HandlerMethod handlerMethod) {
		return true;
	}

boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
		for (int i = 0; i < this.interceptorList.size(); i++) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			if (!interceptor.preHandle(request, response, this.handler)) {
				triggerAfterCompletion(request, response, null);
				return false;
			}
			this.interceptorIndex = i;
		}
		return true;
	}

				if (!mappedHandler.applyPreHandle(processedRequest, response)) {
					return;
				}

@Override
	protected ModelAndView handleInternal(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {

		ModelAndView mav;
		checkRequest(request);

		// Execute invokeHandlerMethod in synchronized block if required.
                          //在会话上同步处理请求
		if (this.synchronizeOnSession) {
			HttpSession session = request.getSession(false);
			if (session != null) {
				Object mutex = WebUtils.getSessionMutex(session);
				synchronized (mutex) {
					mav = invokeHandlerMethod(request, response, handlerMethod);
				}
			}
			else {
				// No HttpSession available -> no mutex necessary
				mav = invokeHandlerMethod(request, response, handlerMethod);
			}
		}
		else {
			// No synchronization on session demanded at all...
                        //调用HandlerMethod的方法
			mav = invokeHandlerMethod(request, response, handlerMethod);
		}

		if (!response.containsHeader(HEADER_CACHE_CONTROL)) {
			if (getSessionAttributesHandler(handlerMethod).hasSessionAttributes()) {
				applyCacheSeconds(response, this.cacheSecondsForSessionAttributeHandlers);
			}
			else {
				prepareResponse(response);
			}
		}

		return mav;
	}

@Nullable
	protected ModelAndView invokeHandlerMethod(HttpServletRequest request,
			HttpServletResponse response, HandlerMethod handlerMethod) throws Exception {
                     //封装request
		ServletWebRequest webRequest = new ServletWebRequest(request, response);
		WebDataBinderFactory binderFactory = getDataBinderFactory(handlerMethod);
		ModelFactory modelFactory = getModelFactory(handlerMethod, binderFactory);
                    //创建ServletInvocableHandlerMethod
		ServletInvocableHandlerMethod invocableMethod = createInvocableHandlerMethod(handlerMethod);
		if (this.argumentResolvers != null) {
			invocableMethod.setHandlerMethodArgumentResolvers(this.argumentResolvers);
		}
		if (this.returnValueHandlers != null) {
			invocableMethod.setHandlerMethodReturnValueHandlers(this.returnValueHandlers);
		}
		invocableMethod.setDataBinderFactory(binderFactory);
		invocableMethod.setParameterNameDiscoverer(this.parameterNameDiscoverer);
                    //创建ModeAndView
		ModelAndViewContainer mavContainer = new ModelAndViewContainer();
		mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
		modelFactory.initModel(webRequest, mavContainer, invocableMethod);
		mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);

		AsyncWebRequest asyncWebRequest = WebAsyncUtils.createAsyncWebRequest(request, response);
		asyncWebRequest.setTimeout(this.asyncRequestTimeout);

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.setTaskExecutor(this.taskExecutor);
		asyncManager.setAsyncWebRequest(asyncWebRequest);
		asyncManager.registerCallableInterceptors(this.callableInterceptors);
		asyncManager.registerDeferredResultInterceptors(this.deferredResultInterceptors);

		if (asyncManager.hasConcurrentResult()) {
			Object result = asyncManager.getConcurrentResult();
			mavContainer = (ModelAndViewContainer) asyncManager.getConcurrentResultContext()[0];
			asyncManager.clearConcurrentResult();
			LogFormatUtils.traceDebug(logger, traceOn -> {
				String formatted = LogFormatUtils.formatValue(result, !traceOn);
				return "Resume with async result [" + formatted + "]";
			});
			invocableMethod = invocableMethod.wrapConcurrentResult(result);
		}
                    //调用目标方法
		invocableMethod.invokeAndHandle(webRequest, mavContainer);
		if (asyncManager.isConcurrentHandlingStarted()) {
			return null;
		}
            //ModelAndView对象
		return getModelAndView(mavContainer, modelFactory, webRequest);
	}

public void invokeAndHandle(ServletWebRequest webRequest, ModelAndViewContainer mavContainer,
			Object... providedArgs) throws Exception {
                        //调用目标方法
		Object returnValue = invokeForRequest(webRequest, mavContainer, providedArgs);
		setResponseStatus(webRequest);

		if (returnValue == null) {
			if (isRequestNotModified(webRequest) || getResponseStatus() != null || mavContainer.isRequestHandled()) {
				disableContentCachingIfNecessary(webRequest);
				mavContainer.setRequestHandled(true);
				return;
			}
		}
		else if (StringUtils.hasText(getResponseStatusReason())) {
			mavContainer.setRequestHandled(true);
			return;
		}

		mavContainer.setRequestHandled(false);
		Assert.state(this.returnValueHandlers != null, "No return value handlers");
		try {
            //返回类型的处理器,如RequestResponseBodyMethodProcessor
			this.returnValueHandlers.handleReturnValue(
					returnValue, getReturnValueType(returnValue), mavContainer, webRequest);
		}
		catch (Exception ex) {
			if (logger.isTraceEnabled()) {
				logger.trace(formatErrorForReturnValue(returnValue), ex);
			}
			throw ex;
		}
	}

/**
	 * Apply postHandle methods of registered interceptors.
	 */
	void applyPostHandle(HttpServletRequest request, HttpServletResponse response, @Nullable ModelAndView mv)
			throws Exception {

		for (int i = this.interceptorList.size() - 1; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			interceptor.postHandle(request, response, this.handler, mv);
		}
	}

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 mavDefiningException) {
				logger.debug("ModelAndViewDefiningException encountered", exception);
				mv = mavDefiningException.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 (logger.isTraceEnabled()) {
				logger.trace("No view rendering, null ModelAndView returned.");
			}
		}

		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);
		}
	}

@Nullable
	protected View resolveViewName(String viewName, @Nullable Map<String, Object> model,
			Locale locale, HttpServletRequest request) throws Exception {

		if (this.viewResolvers != null) {
			for (ViewResolver viewResolver : this.viewResolvers) {
				View view = viewResolver.resolveViewName(viewName, locale);
				if (view != null) {
					return view;
				}
			}
		}
		return null;
	}

@Override
	public void render(@Nullable Map<String, ?> model, HttpServletRequest request,
			HttpServletResponse response) throws Exception {

		if (logger.isDebugEnabled()) {
			logger.debug("View " + formatViewName() +
					", model " + (model != null ? model : Collections.emptyMap()) +
					(this.staticAttributes.isEmpty() ? "" : ", static attributes " + this.staticAttributes));
		}

		Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);
		prepareResponse(request, response);
		renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);
	}

void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, @Nullable Exception ex) {
		for (int i = this.interceptorIndex; i >= 0; i--) {
			HandlerInterceptor interceptor = this.interceptorList.get(i);
			try {
				interceptor.afterCompletion(request, response, this.handler, ex);
			}
			catch (Throwable ex2) {
				logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
			}
		}
	}

/**
 * 拦截器1
 *
 * @author zouhl
 */
public class MyInterceptA implements HandlerInterceptor {
    private static final Logger LOGGER = LoggerFactory.getLogger(MyInterceptA.class);

    /**
     * 前置处理
     *
     * @param request  current HTTP request
     * @param response current HTTP response
     * @param handler  chosen handler to execute, for type and/or instance evaluation
     * @return 是否执行后续的拦截器和handle方法
     * @throws Exception
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        LOGGER.info("MyInterceptA preHandle");
        return true;
    }
    /**
     * 后置处理
     *
     * @param request      current HTTP request
     * @param response     current HTTP response
     * @param handler      the handler (or {@link HandlerMethod}) that started asynchronous
     *                     execution, for type and/or instance examination
     * @param modelAndView the {@code ModelAndView} that the handler returned
     *                     (can also be {@code null})
     * @throws Exception
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
                           @Nullable ModelAndView modelAndView) throws Exception {
        LOGGER.info("MyInterceptA postHandle");
    }

    /**
     * 最终处理，我自己翻译的
     *
     * @param request  current HTTP request
     * @param response current HTTP response
     * @param handler  the handler (or {@link HandlerMethod}) that started asynchronous
     *                 execution, for type and/or instance examination
     * @param ex       any exception thrown on handler execution, if any; this does not
     *                 include exceptions that have been handled through an exception resolver
     * @throws Exception
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
                                @Nullable Exception ex) throws Exception {
        LOGGER.info("MyInterceptA afterCompletion");
    }
}

/**
 * 一个简单的过滤器
 *
 * @author zouhl
 */
@WebFilter("/*")
public class MyFilter extends HttpFilter {
    private static final Logger LOGGER = LoggerFactory.getLogger(MyFilter.class);

    /**
     * @param req   a {@link ServletRequest} object that contains the request the client has made of the filter
     * @param res   a {@link ServletResponse} object that contains the response the filter sends to the client
     * @param chain the <code>FilterChain</code> for invoking the next filter or the resource
     * @throws IOException
     * @throws ServletException
     */
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
            throws IOException, ServletException {
        if (!(req instanceof HttpServletRequest && res instanceof HttpServletResponse)) {
            throw new ServletException("non-HTTP request or response");
        }
        beforeDo(req);
        chain.doFilter(req, res);
        afterDo(req, res);
    }

    /**
     * 前置处理
     * @param req
     * @param res
     */
    private void afterDo(ServletRequest req, ServletResponse res) {
        LOGGER.info("MyFilter.afterDo()");
    }

    /**
     * 后置处理
     * @param req
     */
    private void beforeDo(ServletRequest req) {
        LOGGER.info("MyFilter.beforeDo()");
    }
}