背景

• 介绍Interceptor的案例。
• Interceptor的解析，HandlerMapping和Interceptor的绑定。
• HandlerExecutionChain的拦截器链的构建。
• HandlerExecutionChain的执行流程。

Interceptor案例

@Component
public class TimeInterceptor extends HandlerInterceptorAdapter {

    private final NamedThreadLocal<Long> startTimeThreadLocal = new NamedThreadLocal<>("startTimeThreadLocal");

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {

        System.out.println("time interceptor postHandle");

        // 获取处理当前请求的 handler 信息
        HandlerMethod handlerMethod = (HandlerMethod) handler;
        System.out.println("handler 类：" + handlerMethod.getBeanType().getName());
        System.out.println("handler 方法：" + handlerMethod.getMethod().getName());

        MethodParameter[] methodParameters = handlerMethod.getMethodParameters();
        for (MethodParameter methodParameter : methodParameters) {
            // 只能获取参数的名称，不能获取到参数的值
            String parameterName = methodParameter.getParameterName();
            System.out.println("parameterName: " + parameterName);
        }

        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("time interceptor postHandle");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

        System.out.println("time interceptor afterCompletion");
    }
}

• 通过继承HandlerInterceptorAdapter实现拦截器类并实现preHandle、postHandle、afterCompletion等方法。

<bean id="xxxx" class="com.lg.mvc.interceptor.TimeInterceptor"/>  
<mvc:interceptors>  
    <mvc:interceptor>  
        <mvc:mapping path="xxx"/>  
        <mvc:exclude-mapping path="xxxx"/>
        <ref bean="logMvcInterceptor"/>
    </mvc:interceptor>  
</mvc:interceptors>  

• 通过在xml文件中定义mvc:interceptors定义拦截器和对应匹配的路径。
• 通过interceptor标签的InterceptorsBeanDefinitionParser解析拦截器定义。

Interceptor解析流程

http\://www.springframework.org/schema/mvc=org.springframework.web.servlet.config.MvcNamespaceHandler


public class MvcNamespaceHandler extends NamespaceHandlerSupport {

    @Override
    public void init() {
        registerBeanDefinitionParser("annotation-driven", new AnnotationDrivenBeanDefinitionParser());
        registerBeanDefinitionParser("default-servlet-handler", new DefaultServletHandlerBeanDefinitionParser());
        registerBeanDefinitionParser("interceptors", new InterceptorsBeanDefinitionParser());
        registerBeanDefinitionParser("resources", new ResourcesBeanDefinitionParser());
        registerBeanDefinitionParser("view-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("redirect-view-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("status-controller", new ViewControllerBeanDefinitionParser());
        registerBeanDefinitionParser("view-resolvers", new ViewResolversBeanDefinitionParser());
        registerBeanDefinitionParser("tiles-configurer", new TilesConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("freemarker-configurer", new FreeMarkerConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("velocity-configurer", new VelocityConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("groovy-configurer", new GroovyMarkupConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("script-template-configurer", new ScriptTemplateConfigurerBeanDefinitionParser());
        registerBeanDefinitionParser("cors", new CorsBeanDefinitionParser());
    }
}

• 通过InterceptorsBeanDefinitionParser来解析interceptors的配置项。

class InterceptorsBeanDefinitionParser implements BeanDefinitionParser {

    @Override
    public BeanDefinition parse(Element element, ParserContext parserContext) {
        CompositeComponentDefinition compDefinition = new CompositeComponentDefinition(element.getTagName(), parserContext.extractSource(element));
        parserContext.pushContainingComponent(compDefinition);

        RuntimeBeanReference pathMatcherRef = null;
        if (element.hasAttribute("path-matcher")) {
            pathMatcherRef = new RuntimeBeanReference(element.getAttribute("path-matcher"));
        }

        List<Element> interceptors = DomUtils.getChildElementsByTagName(element, "bean", "ref", "interceptor");
        for (Element interceptor : interceptors) {
            RootBeanDefinition mappedInterceptorDef = new RootBeanDefinition(MappedInterceptor.class);
            mappedInterceptorDef.setSource(parserContext.extractSource(interceptor));
            mappedInterceptorDef.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);

            ManagedList<String> includePatterns = null;
            ManagedList<String> excludePatterns = null;
            Object interceptorBean;
            if ("interceptor".equals(interceptor.getLocalName())) {
                includePatterns = getIncludePatterns(interceptor, "mapping");
                excludePatterns = getIncludePatterns(interceptor, "exclude-mapping");
                Element beanElem = DomUtils.getChildElementsByTagName(interceptor, "bean", "ref").get(0);
                interceptorBean = parserContext.getDelegate().parsePropertySubElement(beanElem, null);
            }
            else {
                interceptorBean = parserContext.getDelegate().parsePropertySubElement(interceptor, null);
            }
            mappedInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(0, includePatterns);
            mappedInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(1, excludePatterns);
            mappedInterceptorDef.getConstructorArgumentValues().addIndexedArgumentValue(2, interceptorBean);

            if (pathMatcherRef != null) {
                mappedInterceptorDef.getPropertyValues().add("pathMatcher", pathMatcherRef);
            }

            String beanName = parserContext.getReaderContext().registerWithGeneratedName(mappedInterceptorDef);
            parserContext.registerComponent(new BeanComponentDefinition(mappedInterceptorDef, beanName));
        }

        parserContext.popAndRegisterContainingComponent();
        return null;
    }
}

• 解析Interceptor的xml配置生成MappedInterceptor的BeanDefinition。
• 每个mvc:interceptor标签解析生成一个MappedInterceptor对象。

public final class MappedInterceptor implements HandlerInterceptor {

    private final String[] includePatterns;
    private final String[] excludePatterns;
    private final HandlerInterceptor interceptor;
    private PathMatcher pathMatcher;

    public MappedInterceptor(String[] includePatterns, HandlerInterceptor interceptor) {
        this(includePatterns, null, interceptor);
    }

    public MappedInterceptor(String[] includePatterns, String[] excludePatterns, HandlerInterceptor interceptor) {
        this.includePatterns = includePatterns;
        this.excludePatterns = excludePatterns;
        this.interceptor = interceptor;
    }

    public MappedInterceptor(String[] includePatterns, WebRequestInterceptor interceptor) {
        this(includePatterns, null, interceptor);
    }

    public MappedInterceptor(String[] includePatterns, String[] excludePatterns, WebRequestInterceptor interceptor) {
        this(includePatterns, excludePatterns, new WebRequestHandlerInterceptorAdapter(interceptor));
    }

    public void setPathMatcher(PathMatcher pathMatcher) {
        this.pathMatcher = pathMatcher;
    }

    public PathMatcher getPathMatcher() {
        return this.pathMatcher;
    }

    public String[] getPathPatterns() {
        return this.includePatterns;
    }

    public HandlerInterceptor getInterceptor() {
        return this.interceptor;
    }

    public boolean matches(String lookupPath, PathMatcher pathMatcher) {
        PathMatcher pathMatcherToUse = (this.pathMatcher != null ? this.pathMatcher : pathMatcher);
        if (!ObjectUtils.isEmpty(this.excludePatterns)) {
            for (String pattern : this.excludePatterns) {
                if (pathMatcherToUse.match(pattern, lookupPath)) {
                    return false;
                }
            }
        }
        if (ObjectUtils.isEmpty(this.includePatterns)) {
            return true;
        }
        for (String pattern : this.includePatterns) {
            if (pathMatcherToUse.match(pattern, lookupPath)) {
                return true;
            }
        }
        return false;
    }

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
            throws Exception {

        return this.interceptor.preHandle(request, response, handler);
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
            ModelAndView modelAndView) throws Exception {

        this.interceptor.postHandle(request, response, handler, modelAndView);
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
            Exception ex) throws Exception {

        this.interceptor.afterCompletion(request, response, handler, ex);
    }
}

• MappedInterceptor包含includePatterns和excludePatterns和interceptor核心变量。
• includePatterns代表包含的匹配路径，excludePatterns代表排除的匹配路径，interceptor代表拦截器对象。
• matches方法负责查找Request匹配的Interceptor对象。

RequestMappingHandlerMapping

• HandlerMapping的构建过程中会建立和Interceptors的关联关系。
• RequestMappingHandlerMapping是HandlerMapping的一种实现形式。
• RequestMappingHandlerMapping的初始化过程中通过父类AbstractHandlerMapping负责建立和Interceptors的关联关系。

public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport implements HandlerMapping, Ordered {

    private Object defaultHandler;
    private UrlPathHelper urlPathHelper = new UrlPathHelper();
    private PathMatcher pathMatcher = new AntPathMatcher();
    private final List<Object> interceptors = new ArrayList<Object>();
    private final List<HandlerInterceptor> adaptedInterceptors = new ArrayList<HandlerInterceptor>();
    private final UrlBasedCorsConfigurationSource globalCorsConfigSource = new UrlBasedCorsConfigurationSource();
    private CorsProcessor corsProcessor = new DefaultCorsProcessor();

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

    protected void detectMappedInterceptors(List<HandlerInterceptor> mappedInterceptors) {
        mappedInterceptors.addAll(
                BeanFactoryUtils.beansOfTypeIncludingAncestors(
                        getApplicationContext(), MappedInterceptor.class, true, false).values());
    }
}

• AbstractHandlerMapping的interceptors和adaptedInterceptors保存Interceptor。
• detectMappedInterceptors保存的是解析生成的MappedInterceptor类。

HandlerExecutionChain

public abstract class AbstractHandlerMapping extends WebApplicationObjectSupport implements HandlerMapping, Ordered {

    private int order = Integer.MAX_VALUE;  // default: same as non-Ordered
    private Object defaultHandler;
    private UrlPathHelper urlPathHelper = new UrlPathHelper();
    private PathMatcher pathMatcher = new AntPathMatcher();
    private final List<Object> interceptors = new ArrayList<Object>();
    private final List<HandlerInterceptor> adaptedInterceptors = new ArrayList<HandlerInterceptor>();
    private final UrlBasedCorsConfigurationSource globalCorsConfigSource = new UrlBasedCorsConfigurationSource();
    private CorsProcessor corsProcessor = new DefaultCorsProcessor();

    @Override
    public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
        Object handler = getHandlerInternal(request);
        HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
        return executionChain;
    }


    protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
        HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
                (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
        // 根据请求的path获取interceptor
        String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
        for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
            if (interceptor instanceof MappedInterceptor) {
                MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
                // 匹配查找对应的interceptor
                if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                    chain.addInterceptor(mappedInterceptor.getInterceptor());
                }
            }
            else {
                chain.addInterceptor(interceptor);
            }
        }
        return chain;
    }
}

• AbstractHandlerMapping的getHandler方法返回HandlerExecutionChain的拦截器链。
• AbstractHandlerMapping的getHandlerExecutionChain遍历adaptedInterceptors添加到HandlerExecutionChain中。

拦截器执行流程

public class DispatcherServlet extends FrameworkServlet {

    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);
                // mappedHandler代表的是HandlerExecutionChain职责链
                mappedHandler = getHandler(processedRequest);
                HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());

                // 执行mappedHandler的applyPreHandle方法
                if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                    return;
                }
                // 执行controller的执行逻辑
                mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                if (asyncManager.isConcurrentHandlingStarted()) {
                    return;
                }
                applyDefaultViewName(processedRequest, mv);
                // 执行mappedHandler的applyPostHandle方法
                mappedHandler.applyPostHandle(processedRequest, response, mv);
            }
            catch (Exception ex) {
            }
            processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
        }
        catch (Exception ex) {
        }
        finally {
        }
    }

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

• mappedHandler.applyPreHandle负责执行拦截器Interceptor的preHandle方法。
• ha.handle负责执行controller的逻辑方法。
• mappedHandler.applyPostHandle负责执行拦截器Interceptor的postHandle方法。

public class HandlerExecutionChain {
    private static final Log logger = LogFactory.getLog(HandlerExecutionChain.class);
    private final Object handler;
    private HandlerInterceptor[] interceptors;
    private List<HandlerInterceptor> interceptorList;
    private int interceptorIndex = -1;

    public HandlerInterceptor[] getInterceptors() {
        if (this.interceptors == null && this.interceptorList != null) {
            this.interceptors = this.interceptorList.toArray(new HandlerInterceptor[this.interceptorList.size()]);
        }
        return this.interceptors;
    }

    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;
    }

    void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = interceptors.length - 1; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                interceptor.postHandle(request, response, this.handler, mv);
            }
        }
    }

    void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
            throws Exception {

        HandlerInterceptor[] interceptors = getInterceptors();
        if (!ObjectUtils.isEmpty(interceptors)) {
            for (int i = this.interceptorIndex; i >= 0; i--) {
                HandlerInterceptor interceptor = interceptors[i];
                try {
                    interceptor.afterCompletion(request, response, this.handler, ex);
                }
                catch (Throwable ex2) {
                }
            }
        }
    }
}

• applyPreHandle负责遍历拦截器的preHandle方法。
• applyPostHandle负责遍历拦截器的postHandle方法。

Filter和Interceptor的调用链

      // 以下是自定义拦截器TimeInterceptor的调用链
      at com.nextyu.demo.web.interceptor.TimeInterceptor.preHandle(TimeInterceptor.java:31)
      at org.springframework.web.servlet.HandlerExecutionChain.applyPreHandle(HandlerExecutionChain.java:133)
      at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:962)
      at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
      at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
      at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
      at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
      // HttpServlet的实例是DispatcherServlet
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
      // 以下是Tomcat的处理逻辑
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      // 以下是自定义Filter对象TimeFilter的调用链
      at com.nextyu.demo.web.filter.TimeFilter.doFilter(TimeFilter.java:25)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at org.springframework.web.filter.HttpPutFormContentFilter.doFilterInternal(HttpPutFormContentFilter.java:108)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:81)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:197)
      at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107)
      at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
      at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
      at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
      at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
      at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:478)
      at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
      at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
      at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
      at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
      at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:803)
      at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
      at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868)
      at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1459)
      at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
      - locked <0x14f6> (a org.apache.tomcat.util.net.NioEndpoint$NioSocketWrapper)
      at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
      at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
      at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
      at java.lang.Thread.run(Thread.java:748)

参考

• mvc:interceptors拦截器介绍