@Component
public class TestInterceptor implements HandlerInterceptor {

    //请求在进入Handler之前,该方法会被调用
    //如果返回true,则表示该请求会继续往下执行,也就是才会执行到Handler
    //如果返回false,就不会执行到Handler,并且另外两个方法也不会执行
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //因为我们使用的是注解形式的处理器(RequestMapping)
        //所以handler对象的真正的类型是HandlerMethod
        HandlerMethod hm = (HandlerMethod) handler;
        //获取该方法的注解对象
//        hm.getMethodAnnotation();
        HttpSession session = request.getSession();
        Object user = session.getAttribute("user");
        if (user != null){

            return  true;  //放行
        }
        response.sendRedirect("/log");  //重定向
        return false;
    }

    /*
    Handler中的方法执行完毕之后,向客户端返回视图之前执行.
    方法参数中的ModelAndView对象就是给客户端渲染所用的对象.

     */
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }
    /*
    这个请求已经给客户端完成了渲染的工作之后,该方法会执行
    这个方法中一般会做资源的清理工作.
     */
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
}

   <mvc:interceptors>
        <mvc:interceptor>
         <!--/**表示所有请求地址都要经过拦截器-->
            <mvc:mapping path="/**"/>
         <!--下面表示这些地址可以不走拦截器-->
            <mvc:exclude-mapping path="/log"/>
            <mvc:exclude-mapping path="/login"/>
            <mvc:exclude-mapping path="/relog"/>
            <mvc:exclude-mapping path="/home"/>
         <!--在拦截器类上加了注解@Component,所以可以直接引入拦截器id,表明上面被拦截的地址需要经过哪个拦截器-->
            <ref bean="testInterceptor"/>
        </mvc:interceptor>
    </mvc:interceptors>

/*
注解上面需要配置这个注解可以用到哪里:
例如:是给类用的,还是给属性用的,还是给方法用的
 */
@Target(ElementType.METHOD)
//这个注解是在运行时候生效的
@Retention(RetentionPolicy.RUNTIME)
public @interface CheckPermission {
    String value();
}

@Controller
public class UserController {

    @CheckPermission("one")
    @RequestMapping("/one")
    public String one(){

        return "one";
    }

    @CheckPermission("two")
    @RequestMapping("/two")
    public String two(){

        return "two";
    }

    @CheckPermission("three")
    @RequestMapping("/three")
    public String three(){

        return "three";
    }

    @CheckPermission("four")
    @RequestMapping("/four")
    public String four(){

        return "four";
    }
}

package com.lanou.demo.interceptor;

import com.lanou.demo.annotation.CheckPermission;
import org.springframework.stereotype.Component;
import org.springframework.web.method.HandlerMethod;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import java.util.List;

@Component
public class TestInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {


        HttpSession session = request.getSession();
        List<String> list = (List<String>) session.getAttribute("arr");
         //获取Handler信息
        HandlerMethod mv = (HandlerMethod) handler;
        //判断这个请求方法是否有这个注解
        if (mv.hasMethodAnnotation(CheckPermission.class)) {
            //通过这个注解获取到请求地址
            CheckPermission annotation = mv.getMethodAnnotation(CheckPermission.class);
            String value = annotation.value();

            if (list != null){
                  //判断这个地址是否有权限
                if (list.contains(value)) {
                    //有权限,放行
                    return true;
                }
            }
        }
        //没有权限,重定向到某个页面
        response.sendRedirect("/log");
        return false;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
}