SpringMVC拦截器

首先添加依赖：

<dependency>
  <groupId>junit</groupId>
  <artifactId>junit</artifactId>
  <version>4.11</version>
  <scope>test</scope>
</dependency>

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-webmvc</artifactId>
  <version>4.3.1.RELEASE</version>
</dependency>

<dependency>
  <groupId>javax</groupId>
  <artifactId>javaee-api</artifactId>
  <version>7.0</version>
  <scope>provided</scope>
</dependency>

配置web.xml：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
		http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

  <servlet>
    <servlet-name>spring</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath*:spring.xml</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>spring</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

</web-app>

配置：spring.xml：

<?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:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-4.3.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context.xsd">

    <context:component-scan base-package="com.fitsoft.controller"/>

    <!-- 拦截器的注册 -->
    <mvc:interceptors>
        <mvc:interceptor>
            <mvc:mapping path="/user/**"/>
            <!-- 排除拦截，一般在通配符中有意义 -->
            <!--<mvc:exclude-mapping path="/user/search"/>-->
            <bean class="com.fitsoft.core.LoginInterceptor"/>
        </mvc:interceptor>
    </mvc:interceptors>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/view/"/>
        <property name="suffix" value=".jsp"/>
    </bean>

</beans>

目录结构大致是这样的：


配置成功之后编写LoginInterceptor拦截器类：

package com.fitsoft.core;

import org.springframework.util.StringUtils;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;

/**
 * @author Joker
 * @since 2019/9/14 0014 15:56
 */
public class LoginInterceptor implements HandlerInterceptor {

    @Override
    public boolean preHandle(javax.servlet.http.HttpServletRequest httpServletRequest, javax.servlet.http.HttpServletResponse httpServletResponse, Object o) throws Exception {

        String user = (String) httpServletRequest.getSession().getAttribute("user_session");

        if(StringUtils.isEmpty(user)){
            System.out.println(httpServletRequest.getContextPath());
            httpServletResponse.sendRedirect(httpServletRequest.getContextPath()+"/login");
            return false;
        }

        System.out.println("keketip=====preHandler===>");

      //  return false;//会终止所有请求
        return true;
    }

    @Override
    public void postHandle(javax.servlet.http.HttpServletRequest httpServletRequest, javax.servlet.http.HttpServletResponse httpServletResponse, Object o, ModelAndView modelAndView) throws Exception {
        
        System.out.println("keketip=====postHandler===>");
    }

    @Override
    public void afterCompletion(javax.servlet.http.HttpServletRequest httpServletRequest, javax.servlet.http.HttpServletResponse httpServletResponse, Object o, Exception e) throws Exception {

        System.out.println("keketip=====afterHandler===>");
    }
}

这里实现HandlerInterceptor接口，主要有三个方法：
preHandle、postHandle 和 afterCompletion
其中preHandle返回true，否则拦截器就失效了，然后在这个方法里处理请求，判断session中的用户是否为空，如果为空则跳转登录界面，不为空则跳转search界面。
login.jsp：

<%--
  Created by IntelliJ IDEA.
  User: Joker
  Date: 2019/9/14 0014
  Time: 16:16
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>Title</title>
</head>
<body>
<h1>登录</h1>
<form action="logined" method="post">
    <label>用户名</label>
    <input name="username" type="text">
    <label>密码</label>
    <input name="password" type="text">
    <button type="submit">登录</button>
</form>
</body>
</html>

这个是登录界面，只有一个form表单也没有样式，做的很简陋
LoginController：

package com.fitsoft.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;

import javax.servlet.http.HttpSession;

/**
 * @author Joker
 * @since 2019/9/14 0014 16:20
 */
@Controller
public class LoginController {


    @RequestMapping("/login")
    public String login(){
        return "login";
    }

    @RequestMapping("/logined")
    public String logined(@RequestParam("username") String username,
                        @RequestParam("password") String password,
                          HttpSession httpSession){

        System.out.println(username);
        System.out.println(password);

        httpSession.setAttribute("user_session", "6666666");

        return "redirect:user/search";
    }
}

我们在登录这个方法里面放入session，登录成功之后跳转到search界面，这样我们的拦截器就会发挥作用了，如果有用户登录，则有session，拦截器放行，如果不进行登录，则没有session，直接访问界面会回到login界面。另外还有一个UserController，访问search跳转到search界面：

package com.fitsoft.controller;

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;

import javax.servlet.http.HttpSession;

/**
 * @author Joker
 * @since 2019/9/14 0014 16:15
 */
@Controller
@RequestMapping("/user")
public class UserController {

    @RequestMapping("/search")
    public String search(HttpSession httpSession){
        return "user/search";
    }
}

不算难，会用就行。