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。

 1 public interface HandlerInterceptor {
 2 
 3     boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
 4             throws Exception;
 5 
 6     void postHandle(
 7             HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
 8             throws Exception;
 9 
10     void afterCompletion(
11             HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex)
12             throws Exception;
13 
14 }

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。

1 public interface AsyncHandlerInterceptor extends HandlerInterceptor {
2 
3     void afterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response, Object handler)
4             throws Exception;
5 
6 }

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

 1 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
 2         try {
 3 
 4             try {
 5                 //.......省略代码
 6 
 7                 //返回HandlerExecutionChain  其中包含了拦截器队列
 8                 mappedHandler = getHandler(processedRequest);
 9 
10                 //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
11                 if (!mappedHandler.applyPreHandle(processedRequest, response)) {
12                     return;
13                 }
14 
15                 // 处理Controller层
16                 mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
17 
18                 applyDefaultViewName(processedRequest, mv);
19 
20                 //调用拦截器的PostHandle方法
21                 mappedHandler.applyPostHandle(processedRequest, response, mv);
22             }
23             catch (Exception ex) {
24                 dispatchException = ex;
25             }
26 
27             processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException);
28         }
29         catch (Exception ex) {
30             //抛出异常后都会调用拦截器AfterCompletion方法
31             triggerAfterCompletion(processedRequest, response, mappedHandler, ex);
32         }
33         finally {
34             if (asyncManager.isConcurrentHandlingStarted()) {
35                 // Instead of postHandle and afterCompletion
36                 if (mappedHandler != null) {
37                     //若Controller方法为异步调用，则执行拦截器afterConcurrentHandlingStarted（只有AsyncHandlerInterceptor拦截器才有）
38                     mappedHandler.applyAfterConcurrentHandlingStarted(processedRequest, response);
39                 }
40             }
41         }
42     }

2.2 获取拦截器

 1 protected void doDispatch(HttpServletRequest request, HttpServletResponse response) throws Exception {
 2     //返回HandlerExecutionChain  其中包含了拦截器队列
 3     mappedHandler = getHandler(processedRequest);
 4 }
 5 //返回HandlerExecutionChain
 6 public final HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception {
 7 
 8     HandlerExecutionChain executionChain = getHandlerExecutionChain(handler, request);
 9     return executionChain;
10 }
11 
12 protected HandlerExecutionChain getHandlerExecutionChain(Object handler, HttpServletRequest request) {
13         HandlerExecutionChain chain = (handler instanceof HandlerExecutionChain ?
14                 (HandlerExecutionChain) handler : new HandlerExecutionChain(handler));
15 
16         //根据url和拦截器异常的配置url做对比，若符合则加入队列
17         String lookupPath = this.urlPathHelper.getLookupPathForRequest(request);
18         for (HandlerInterceptor interceptor : this.adaptedInterceptors) {
19             if (interceptor instanceof MappedInterceptor) {
20                 MappedInterceptor mappedInterceptor = (MappedInterceptor) interceptor;
21                 if (mappedInterceptor.matches(lookupPath, this.pathMatcher)) {
22                     chain.addInterceptor(mappedInterceptor.getInterceptor());
23                 }
24             }
25             else {
26                 chain.addInterceptor(interceptor);
27             }
28         }
29         return chain;
30 }
31 
32 public boolean matches(String lookupPath, PathMatcher pathMatcher) {
33         PathMatcher pathMatcherToUse = (this.pathMatcher != null) ? this.pathMatcher : pathMatcher;
34         if (this.excludePatterns != null) {
35             for (String pattern : this.excludePatterns) {
36                 if (pathMatcherToUse.match(pattern, lookupPath)) {
37                     return false;
38                 }
39             }
40         }
41         if (this.includePatterns == null) {
42             return true;
43         }
44         else {
45             for (String pattern : this.includePatterns) {
46                 if (pathMatcherToUse.match(pattern, lookupPath)) {
47                     return true;
48                 }
49             }
50             return false;
51         }
52 }

上述的拦截器的信息，都来自与下面的配置文件

 1 <!-- 拦截器链 -->
 2     <mvc:interceptors>
 3 
 4         <mvc:interceptor>
 5             <!--拦截器mapping 符合的才会执行拦截器-->
 6             <mvc:mapping path="/**"/>
 7             <!--在拦截器mapping中除去下面的url -->
 8             <mvc:exclude-mapping path="/transactional_test/*"/>
 9             <!--执行的拦截器-->
10             <ref bean="apiInterceptor"/>
11         </mvc:interceptor>
12     </mvc:interceptors>
13 
14     <bean id="apiInterceptor" class="com.lk.dome.interceptor.ApiInterceptor"/>
15 ---------------------

2.3 处理拦截器

 1 boolean applyPreHandle(HttpServletRequest request, HttpServletResponse response) throws Exception {
 2         HandlerInterceptor[] interceptors = getInterceptors();
 3         if (!ObjectUtils.isEmpty(interceptors)) {
 4             for (int i = 0; i < interceptors.length; i++) {
 5                 HandlerInterceptor interceptor = interceptors[i];
 6                 //若返回false，则直接执行拦截器的triggerAfterCompletion方法
 7                 if (!interceptor.preHandle(request, response, this.handler)) {
 8                     triggerAfterCompletion(request, response, null);
 9                     //直接返回，在外层的doDispatch逻辑中不执行后面的逻辑
10                     return false;
11                 }
12                 //记录成功执行的拦截器个数
13                 this.interceptorIndex = i;
14             }
15         }
16         return true;
17 }
18 void applyPostHandle(HttpServletRequest request, HttpServletResponse response, ModelAndView mv) throws Exception {
19         HandlerInterceptor[] interceptors = getInterceptors();
20         if (!ObjectUtils.isEmpty(interceptors)) {
21             //拦截器队列从后往前之心，顺序相反
22             for (int i = interceptors.length - 1; i >= 0; i--) {
23                 HandlerInterceptor interceptor = interceptors[i];
24                 interceptor.postHandle(request, response, this.handler, mv);
25             }
26         }
27 }
28 void triggerAfterCompletion(HttpServletRequest request, HttpServletResponse response, Exception ex)
29             throws Exception {
30 
31         HandlerInterceptor[] interceptors = getInterceptors();
32         if (!ObjectUtils.isEmpty(interceptors)) {
33             //interceptorIndex为执行成功的拦截器标志
34             for (int i = this.interceptorIndex; i >= 0; i--) {
35                 HandlerInterceptor interceptor = interceptors[i];
36                 try {
37                     interceptor.afterCompletion(request, response, this.handler, ex);
38                 }
39                 catch (Throwable ex2) {
40                     logger.error("HandlerInterceptor.afterCompletion threw exception", ex2);
41                 }
42             }
43         }
44 }
45 //异步方法调用，拦截器必须属于AsyncHandlerInterceptor接口
46 void applyAfterConcurrentHandlingStarted(HttpServletRequest request, HttpServletResponse response) {
47         HandlerInterceptor[] interceptors = getInterceptors();
48         if (!ObjectUtils.isEmpty(interceptors)) {
49             for (int i = interceptors.length - 1; i >= 0; i--) {
50                 if (interceptors[i] instanceof AsyncHandlerInterceptor) {
51                     try {
52                         AsyncHandlerInterceptor asyncInterceptor = (AsyncHandlerInterceptor) interceptors[i];
53                         asyncInterceptor.afterConcurrentHandlingStarted(request, response, this.handler);
54                     }
55                     catch (Throwable ex) {
56                         logger.error("Interceptor [" + interceptors[i] + "] failed in afterConcurrentHandlingStarted", ex);
57                     }
58                 }
59             }
60         }
61 }