开发权限验证拦截器

//登录页面判断
@RequestMapping("/login")
public String login(String name, String password, HttpServletRequest request){
    //equalsIgnoreCase: 忽略大小写
    if("zar".equalsIgnoreCase(name)&& "123".equalsIgnoreCase(password)){
        //在Session中存储用户信息，用于进行权限验证
        //以后是从数据库中查询数据库中的详细信息
        request.getSession().setAttribute("users",name);
        return "main";
    }else {
        request.setAttribute("errMsg","用户名或密码不正确");
        return "login";
    }
}

开发拦截器

没有强制让我们实现(没报错)?

看这个接口

package org.springframework.web.servlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.lang.Nullable;
import org.springframework.web.method.HandlerMethod;
public interface HandlerInterceptor {
   default boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
         throws Exception {
      return true;
   }
   default void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler,
         @Nullable ModelAndView modelAndView) throws Exception {
   }
   default void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler,
         @Nullable Exception ex) throws Exception {
   }
}

**default**有默认实现，这是**JDK8**以后的新特性,以后你需要哪个功能，你就重写哪个方法就行

因为只有预处理，才可以判断是否放行,所以返回值是**布尔类型**，其余俩个方法，都是处理完后的返回，所以是**void**

package com.chentianyu.interceptor;
import org.springframework.web.servlet.HandlerInterceptor;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class LoginInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //是否登录过的判断
        if(request.getSession().getAttribute("users") == null){
            //此时就是没有登录，返回登录，并给出提示
            request.setAttribute("noLoginWar","您还没有登录，请先登录!");
            request.getRequestDispatcher("/WEB-INF/jsp/login.jsp").forward(request,response);
            return false;
        }
        return true;//放行请求
    }
}

注册拦截器

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/mvc https://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <context:component-scan base-package="com.chentianyu.controller" />
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/jsp/" />
        <property name="suffix" value=".jsp" />
    </bean>
    <mvc:default-servlet-handler />
    <mvc:annotation-driven />
    <!--注册拦截器-->
    <mvc:interceptors>
        <!--多个拦截器会形成拦截器链-->
        <mvc:interceptor>
            <!--映射要拦截的请求-->
            <mvc:mapping path="/**"/>
            <!--拦截了所有，就连登录也拦截了，这样你的项目永远都不能访问到-->
            <!--设置放行的请求-->
            <mvc:exclude-mapping path="/showLogin"/>
            <mvc:exclude-mapping path="/login"/>
            <!--配置具体的拦截器实现功能的类-->
            <bean class="com.chentianyu.interceptor.LoginInterceptor"></bean>
        </mvc:interceptor>
        <!--<mvc:interceptor>
            <mvc:mapping path=""/>
            <
        </mvc:interceptor>-->
    </mvc:interceptors>
</beans>

我们先把浏览器关闭，再次打开，这一步是为了让session失效，然后访问[http://localhost:8080/showMain](http://localhost:8080/showMain)

其实效果已经出现了。登陆后

再开一个窗口访问[http://localhost:8080/showMain](http://localhost:8080/showMain)
就能访问到这个页面(就是什么都没写，只有一个标题而已)