1、建立攔截器

package com.example.demo.interceptor;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
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;

/**
 * 〈一句話功能簡述〉<br>
 * 〈攔截器〉
 *
 * @author 丶Zh1Guo
 * @create 2018/11/22
 * @since 1.0.0
 */
public class LoginInterceptor implements HandlerInterceptor {
    private Logger logger = LoggerFactory.getLogger(LoginInterceptor.class);

    // 在請求處理之前，只有返回true才會執行請求
 

    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        logger.info("[攔截器]啟動登入狀態攔截");
        // 得到session
        HttpSession session = request.getSession();
        logger.info("[攔截器]sessionID:" + session.getId());
        
 
// 得到使用者資訊
        Object userInfo = session.getAttribute("userInfo");
        //判斷使用者是否登入
        if (userInfo != null) {
            logger.info("[攔截器]使用者已經登入,使用者名稱，密碼：" + session.getAttribute("userInfo"));
            return true;
        } else {
            //不存在跳轉至登入頁
            response.sendRedirect(request.getContextPath() + "/");    // 跳轉到首頁登入
            logger.info("[攔截器]使用者沒有登入,已跳轉到:" + request.getContextPath() + "/");
            return false;
        }
    }

    // 檢視渲染後執行
    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {

    }

    // 請求處理後，檢視渲染前
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {

    }
}

2、.繼承WebMvcConfigureAdapter類，覆蓋其addInterceptors介面,註冊自定義的攔截器

@Configuration 註解一定要有

package com.example.demo.interceptor;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

/**
 * 〈一句話功能簡述〉<br>
 * 〈自定義配置類〉
 *
 * @author 丶Zh1Guo
 * @create 2018/11/22
 * @since 1.0.0
 */
@Configuration
public class LoginConfig implements WebMvcConfigurer {

    /**
     * 該方法用於註冊攔截器
     * 可註冊多個攔截器，多個攔截器組成一個攔截器鏈
     */
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // addPathPatterns 新增路徑
        // excludePathPatterns 排除路徑
        registry.addInterceptor(new LoginInterceptor())
                .addPathPatterns("/sys/*"); // 攔截sys路徑下的url
//              .excludePathPatterns("");
    }
}

3、LoginController

/**
 * Copyright (C), 2017-2018, XXX有限公司
 * FileName: LoginController
 * Author:   丶Zh1Guo
 * Date:     2018/11/22 11:10
 * Description: 登入
 * History:
 * <author>          <time>          <version>          <desc>
 * 作者姓名           修改時間           版本號              描述
 */
package com.example.demo.controller;

import com.example.demo.dao.UserDAO;
import com.example.demo.pojo.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.ResponseBody;

import javax.servlet.http.HttpServletRequest;

/**
 * 〈一句話功能簡述〉<br>
 * 〈登入〉
 *
 * @author 丶Zh1Guo
 * @create 2018/11/22
 * @since 1.0.0
 */
@Controller
public class LoginController {
    // 日誌
    private Logger logger = LoggerFactory.getLogger(LoginController.class);

    @Autowired
    private UserDAO userDAO;


    // 啟動服務自動跳轉登入
//    @RequestMapping(value = {"/", "/login"})
    @RequestMapping(value = "/")
    public String login() {
        return "login";
    }

    // 登入
    @RequestMapping(value = "/loginCheck", method = RequestMethod.POST)
    @ResponseBody
    public String loginCheck(HttpServletRequest request) {
        // 獲取登入資訊
        String userName = request.getParameter("userName");
        String password = request.getParameter("password");

        // 封裝成物件
        User user = new User();
        user.setUserName(userName);
        user.setPassword(password);

        // 校驗使用者資訊
        User info = userDAO.checkUser(user);
        if (info != null) {
            request.getSession().setAttribute("userInfo", userName + "-" + password);
            logger.info("登入成功，使用者名稱：" + userName + "密碼：" + password);
            return "success";
        } else {
            logger.info("登入失敗，使用者名稱：" + userName + "密碼：" + password);
            return "fail";
        }
    }
}

4、未登入會自動跳轉到登入頁面