springboot 提供了集中拦截机制，可以方便我们在业务层进行扩展，熟悉的有 filter、interceptor、Aspect。像 ControllerAdvice 仅用于处理 controller 异常事比较多的，所以再次不过多介绍。下图介绍了机制所在层次：

Filter 过滤器

实现方式有两种，过滤器无法获得上下文、值栈里的对象，并对所有请求起作用

第一种

实现 Filter 接口

package com.wt.cloud.filter;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;

import javax.servlet.*;
import java.io.IOException;

@Component
@Slf4j
public class MyFilter implements Filter {
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        log.info("初始化");
    }

    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
        log.info("执行");
        filterChain.doFilter(servletRequest,servletResponse);
    }

    @Override
    public void destroy() {
        log.info("销毁");
    }
}

第二种

配置到 Bean

package com.wt.cloud.config;

import com.wt.cloud.filter.MyFilter;
import org.springframework.boot.web.servlet.FilterRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

import java.util.Arrays;

@Configuration
public class FilterConfig {

    @Bean
    public FilterRegistrationBean myFilter(){
        FilterRegistrationBean filterRegistrationBean = new FilterRegistrationBean();
        filterRegistrationBean.setFilter(new MyFilter());
        filterRegistrationBean.setUrlPatterns(Arrays.asList("/*"));
        return filterRegistrationBean;
    }
}

Interceptor 拦截器

拦截器可以获取 IOC 容器中的各个 bean, 拦截器是基于 java 的反射机制的，拦截器只能对 action 请求起作用，拦截器可以访问 action 上下文、值栈里的对象，但无法获取参数。

一、实现 HandlerInterceptor 接口

package com.wt.cloud.filter;

import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@Slf4j
@Component
public class MyInterceptor implements HandlerInterceptor{

    /**
     * 功能描述: 执行方法前
     * @return : boolean
     * @author : big uncle
     * @date : 2019/10/9 12:24
     */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        log.info("执行方法前");
        return false;
    }

    /**
     * 功能描述: 执行方法后，有异常不执行
     * @return : boolean
     * @author : big uncle
     * @date : 2019/10/9 12:24
     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        log.info("执行方法后，有异常不执行");
    }

    /**
     * 功能描述: 执行完一定会执行
     * @return : boolean
     * @author : big uncle
     * @date : 2019/10/9 12:24
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        log.info("执行完一定会执行");
    }
}

二、注册到 InterceptorRegistration

package com.wt.cloud.config;

import com.wt.cloud.filter.MyInterceptor;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;


@Configuration
public class InterceptorConfig implements WebMvcConfigurer{

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        //註冊TestInterceptor拦截器 new 或者 注入 都行
        InterceptorRegistration registration = registry.addInterceptor(new MyInterceptor());
        //所有路径都被拦截
        registration.addPathPatterns("/**");
        //添加不拦截路径
        registration.excludePathPatterns("/","/error","/static/**");
    }
}

Aspect 切面

Aspect 可以自定义要切入的类甚至再细的方法，粒度最小。

package com.wt.cloud.filter;

import lombok.extern.slf4j.Slf4j;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.*;
import org.springframework.stereotype.Component;

@Aspect
@Component
@Slf4j
public class MyAspect {

//    @Before("execution(* com.wt.cloud.web.HelloWeb.*(..))")
//    public void Before(JoinPoint point){
//        log.info("执行前");
//    }
//    @After("execution(* com.wt.cloud.web.HelloWeb.*(..))")
//    public void After(JoinPoint point){
//        log.info("执行后");
//    }
//    @AfterThrowing("execution(* com.wt.cloud.web.HelloWeb.*(..))")
//    public void AfterThrowing(JoinPoint point){
//        log.info("执行异常");
//    }

    @Around("execution(* com.wt.cloud.web.HelloWeb.*(..))")
    public Object Around(ProceedingJoinPoint point) throws Throwable {
        log.info("MyAspect 环绕执行");
        log.info("MyAspect 参数 ",point.getArgs());
        Object obj = point.proceed();
        log.info("MyAspect 执行完成结果 ",obj);
        return obj;
    }
}