Sring使用拦截器，如果Controller抛出异常，postHandle不执行

痛定思痛。 2022-05-15 14:52 728阅读 0赞

我的Springboot应用中使用拦截器做限流，在preHandle中申请许可，在执行完之后归还许可，一开始是在postHandle中归还许可，但后来发现，如果接口不自己处理异常，而是抛出异常，则可用的许可越来越少，即，接口抛出异常，则postHandle中的归还许可代码不会执行。

解决办法：

把归还许可的代码放到afterCompletion方法中即可，原因见下面的源码（org.springframework.web.servlet.HandlerExecutionChain），即使preHandle执行不成功，则直接执行触发afterCompletion方法的triggerAfterCompletion方法：

/**
    	 * Apply preHandle methods of registered interceptors.
    	 * @return {@code true} if the execution chain should proceed with the
    	 * next interceptor or the handler itself. Else, DispatcherServlet assumes
    	 * that this interceptor has already dealt with the response itself.
    	 */
    	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;
    	}

附上拦截器源码：

@Override
        public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
            logger.info("Init permits numbers : " + RateLimiterMap.permit.availablePermits());
    
            boolean acq = RateLimiterMap.permit.tryAcquire();//获取许可
    
            logger.info("Permits available numbers : " + RateLimiterMap.permit.availablePermits());
    
            if(!acq){
                //无可用许可，直接抛出异常
                throw new GraphOperateException("The whole request amount has exceed the ability that Model Service can afford");
            }
            return true;
        }
    
        @Override
        public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
            logger.info("postHandle was executed");
        }
    
        @Override
        public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
            RateLimiterMap.permit.release();//归还许可
            logger.info("AfterCompletion was executed: Permits available numbers : " + RateLimiterMap.permit.availablePermits());
        }