前言

在开发过程中，我们常常使用到拦截器来处理一些逻辑。最常用的三种拦截器分别是 AOP、 Interceptor 、 Filter，但其实很多人并不知道什么时候用AOP，什么时候用Interceptor，什么时候用Filter，也不知道其拦截顺序，内部原理。今天我们详细介绍一下这三种拦截器。

拦截器顺序

我们现在有一个controller接口，叫做test，现在我们在项目有定义了三个拦截器，其顺序如下

Filter(before) > Interceptor(before) > AOP(before) > test方法 > AOP(after) > Interceptor(after) > Filter(after)

具体流程如下两幅图片。

所以有时候我们使用不了AOP/Interceptor, 只能使用Filter。

• 比如我们现在是一个Get请求，但是别人却发送了一个Post请求，这时候只有Filter才能拦截，只能使用Filter.
• 又比如我们在Interceptor获取了请求参数以后，因为是一个流，后面controller就会获取不到，我们一般会采用包装类来实现重复读取。但假如我们直接使用AOP就完全可以避免这个问题了。

类似的例子比较多，所以我们应该知其然，也要知其所以然。下面我们介绍一下三种拦截器的具体用法。

Filter拦截器

filter是servlet层面的提供拦截器，和spring无关。只是说现在spring/springboot一统江湖，很多项目在spring的基础上面使用filter。那我们如果在spring项目中使用filter拦截器呢

@Slf4jpublic class FirstFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {log.info("FirstFilter before doFilter");filterChain.doFilter(servletRequest, servletResponse);}}@Slf4jpublic class SecondFilter implements Filter {@Overridepublic void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {log.info("SecondFilter before doFilter");filterChain.doFilter(servletRequest, servletResponse);}}@Slf4j@Configurationpublic class FilterConfig {@Beanpublic FilterRegistrationBean firstFilter() {FilterRegistrationBean registration = new FilterRegistrationBean();registration.setFilter(new FirstFilter());registration.addUrlPatterns("/*");registration.setName("FirstFilter");// 数字越小，优先级越高registration.setOrder(1);return registration;}@Beanpublic FilterRegistrationBean secondFilter() {FilterRegistrationBean registration = new FilterRegistrationBean();registration.setFilter(new SecondFilter());registration.addUrlPatterns("/*");registration.setName("SecondFilter");// 数字越大，优先级越低registration.setOrder(2);return registration;}}

输出结果

FirstFilter before doFilter

SecondFilter before doFilter

Interceptor拦截器

Interceptor是springmvc给我们提供的拦截器，只有在sotingmvc中才可以使用

@Slf4j@Componentpublic class FirstInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {log.info("FirstInterceptor preHandle");return true;}}@Slf4j@Componentpublic class SecondInterceptor implements HandlerInterceptor {@Overridepublic boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)throws Exception {log.info("SecondInterceptor preHandle");return true;}}@Configurationpublic class InterceptorConfig implements WebMvcConfigurer {@Autowiredprivate FirstInterceptor firstInterceptor;@Autowiredprivate SecondInterceptor secondInterceptor;// 配置拦截规则public void addInterceptors(InterceptorRegistry registry) {// 按照注册的顺序，依次执行registry.addInterceptor(firstInterceptor).addPathPatterns("/**").excludePathPatterns("/task/**");registry.addInterceptor(secondInterceptor).addPathPatterns("/**").excludePathPatterns("/spring/**");}}

输出结果

FirstInterceptor preHandle

SecondInterceptor preHandle

AOP拦截器

AOP是我们非常常用的拦截器，织入点，有before，after，around等，我们今天以around为例

@Aspect@Componentpublic class LoggerAOP {@Pointcut("execution (public * com.xxx.controller..*(..))")public void pointcutLogger() {}@Around("pointcutLogger()")public Object methodAround(ProceedingJoinPoint joinPoint) throws Throwable {try {logger.info("request className = {}, method = {}, ip = {}, param = {}", className, methodName, ip, param);resp = joinPoint.proceed();long duration = stopwatch.elapsed(TimeUnit.MILLISECONDS);logger.info("response className = {}, method = {}, resp = {}, cost = {}ms", className, methodName, buildResp(resp), duration);}catch (Throwable e) {logger.error("logger request className = {}, method = {} fail message = {}",className, methodName, e.getMessage(), e);throw e;}return resp;}}

最后

我们介绍了一下spring中，常用的三种拦截器，以及他们在springboot中如何使用。

最后给大家出一个小作业，如果把上面三个拦截器放到一个项目中，他会输出什么顺序呢？

[INFO 2024-07-27 16:01:52.146] [http-nio-8099-exec-2] [] - [FirstFilter.doFilter:17] [FirstFilter before doFilter][INFO 2024-07-27 16:01:52.146] [http-nio-8099-exec-2] [] - [SecondFilter.doFilter:17] [SecondFilter before doFilter][INFO 2024-07-27 16:01:52.148] [http-nio-8099-exec-2] [] - [FirstInterceptor.preHandle:18] [FirstInterceptor preHandle][INFO 2024-07-27 16:01:52.148] [http-nio-8099-exec-2] [] - [SecondInterceptor.preHandle:18] [SecondInterceptor preHandle][INFO 2024-07-27 16:01:52.148] [http-nio-8099-exec-2] [cdc644d0-afdf-4283-bf52-fc5fdd217746] - [LoggerAOP.methodAround:52] [request className = TestController, method = testController, ip = 0:0:0:0:0:0:0:1, param = [null]][INFO 2024-07-27 16:01:52.149] [http-nio-8099-exec-2] [cdc644d0-afdf-4283-bf52-fc5fdd217746] - [TestController.testController:57] [main process][INFO 2024-07-27 16:01:52.149] [http-nio-8099-exec-2] [cdc644d0-afdf-4283-bf52-fc5fdd217746] - [LoggerAOP.methodAround:62] [response className = TestController, method = testController, resp ="ok", cost = 0ms]