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

@Slf4j
public class FirstFilter implements Filter {
	@Override
	public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
		log.info("FirstFilter before doFilter");
		filterChain.doFilter(servletRequest, servletResponse);
	}
}
@Slf4j
public class SecondFilter implements Filter {
	@Override
	public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
		log.info("SecondFilter before doFilter");
		filterChain.doFilter(servletRequest, servletResponse);
	}
}
@Slf4j
@Configuration
public class FilterConfig {
	@Bean
	public 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;
	}
	@Bean
	public 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
@Component
public class FirstInterceptor implements HandlerInterceptor {
	@Override
	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		log.info("FirstInterceptor preHandle");
		return true;
	}
}
@Slf4j
@Component
public class SecondInterceptor implements HandlerInterceptor {
	@Override
	public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
			throws Exception {
		log.info("SecondInterceptor preHandle");
		return true;
	}
}
@Configuration
public class InterceptorConfig implements WebMvcConfigurer {
	@Autowired
	private FirstInterceptor firstInterceptor;
	@Autowired
	private 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
@Component
public 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]