springMVC之Interceptor拦截器

转自：https://blog.csdn.net/qq_25673113/article/details/79153547

Interceptor拦截器用于拦截Controller层接口，表现形式有点像Spring的AOP，但是AOP是针对单一的方法。Interceptor是针对Controller接口以及可以处理request和response对象。

1 HandlerInterceptor接口的定义
我们先来看下HandlerInterceptor接口的定义，定义了三个接口，分别是preHandle、postHandle、afterCompletion。

 public interface HandlerInterceptor {

     boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
             throws Exception;

     void postHandle(
             HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
             throws Exception;

     void afterCompletion(
             HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
             throws Exception;

 }

preHandle是调用Controller之前被调用，当返回false后，会跳过之后的拦截器，并且不会执行所有拦截器的postHandle，并调用返回true的拦截器的afterCompletion方法。
postHandle是调用Controller之后被调用，但是在渲染View页面之前。
afterCompletion是调用完Controller接口，渲染View页面最后调用。返回true的拦截器都会调用该拦截器的afterCompletion方法，顺序相反。

和HandlerInterceptor很相似的要有一个AsyncHandlerInterceptor接口，只是多了个afterConcurrentHandlingStarted个方法，当接口使用了异步的方法的时候调用。

 public interface AsyncHandlerInterceptor extends HandlerInterceptor {

     void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler)
             throws Exception;

 }

2 HandlerInterceptor接口的定义

2.1 DispatcherServlet里doDispatch主处理逻辑

DispatcherServlet里doDispatch()就是springMVC的处理主要逻辑。因此肯定包含了拦截器的主要处理逻辑

 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
         try {

             try {
                 //.......省略代码

                 //返回HandlerExecutionChain  其中包含了拦截器队列
                 mappedHandler = getHandler(processedRequest);

                 //调用拦截器PreHandle方法，若返回false不执行Controller逻辑，并不调用下面的PostHandle方法
                 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
                     return;
                 }

                 // 处理Controller层
                 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());

                 applyDefaultViewName(processedRequest, mv);

                 //调用拦截器的PostHandle方法
                 mappedHandler.applyPostHandle(processedRequest, response, mv);
             }
             catch (Exception ex) {
                 dispatchException = ex;
             }

             processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
         }
         catch (Exception ex) {
             //抛出异常后都会调用拦截器AfterCompletion方法
             triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
         }
         finally {
             if (asyncManager.isConcurrentHandlingStarted()) {
                 // Instead of postHandle and afterCompletion
                 if (mappedHandler != null) {
                     //若Controller方法为异步调用，则执行拦截器afterConcurrentHandlingStarted（只有AsyncHandlerInterceptor拦截器才有）
                     mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
                 }
             }
         }
     }

2.2 获取拦截器

 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
     //返回HandlerExecutionChain  其中包含了拦截器队列
     mappedHandler = getHandler(processedRequest);
 }
 //返回HandlerExecutionChain
 public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {

     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url和拦截器异常的配置url做对比，若符合则加入队列
         String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
         for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
             if (interceptor instanceof MappedInterceptor) {
                 MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
                 if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
                     chain.addInterceptor(mappedInterceptor.getInterceptor());
                 }
             }
             else {
                 chain.addInterceptor(interceptor);
             }
         }
         return chain;
 }

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

上述的拦截器的信息，都来自与下面的配置文件

 <!-- 拦截器链 -->
     <mvc:interceptors>

         <mvc:interceptor>
             <!--拦截器mapping 符合的才会执行拦截器-->
             <mvc:mapping path="/**"/>
             <!--在拦截器mapping中除去下面的url -->
             <mvc:exclude-mapping path="/transactional_test/*"/>
             <!--执行的拦截器-->
             <ref bean="apiInterceptor"/>
         </mvc:interceptor>
     </mvc:interceptors>

     <bean id="apiInterceptor" class="com.lk.dome.interceptor.ApiInterceptor"/>
 --------------------- 

2.3 处理拦截器

 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];
                 //若返回false，则直接执行拦截器的triggerAfterCompletion方法
                 if (!interceptor.preHandle(request, response, this.handler)) {
                     triggerAfterCompletion(request, response, null);
                     //直接返回，在外层的doDispatch逻辑中不执行后面的逻辑
                     return false;
                 }
                 //记录成功执行的拦截器个数
                 this.interceptorIndex = i;
             }
         }
         return true;
 }
 void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
         HandlerInterceptor[] interceptors = getInterceptors();
         if (!ObjectUtils.isEmpty(interceptors)) {
             //拦截器队列从后往前之心，顺序相反
             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)) {
             //interceptorIndex为执行成功的拦截器标志
             for (int i = this.interceptorIndex; i >= 0; i--) {
                 HandlerInterceptor interceptor = interceptors[i];
                 try {
                     interceptor.afterCompletion(request, response, this.handler, ex);
                 }
                 catch (Throwable ex2) {
                     logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
                 }
             }
         }
 }
 //异步方法调用，拦截器必须属于AsyncHandlerInterceptor接口
 void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
         HandlerInterceptor[] interceptors = getInterceptors();
         if (!ObjectUtils.isEmpty(interceptors)) {
             for (int i = interceptors.length - 1; i >= 0; i--) {
                 if (interceptors[i] instanceof AsyncHandlerInterceptor) {
                     try {
                         AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
                         asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
                     }
                     catch (Throwable ex) {
                         logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
                     }
                 }
             }
         }
 }