1：在config层中新建LoginHandlerInterceptor类，使得这个类继承HandlerInterceptor并重写方法

2：在controller层中写可以传入用户session的方法，首先添加HttpSession在具体业务前面传入session的值

3：在LoginHandlerInterceptor类中编写代码：

package com.example.springbootweb.config;

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

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

/**
 * @author ${范涛之}
 * @Description
 * @create 2021-09-19 16:16
 */
public class LoginHandlerInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //登陆成功之后，应该有用户的session
        Object loginUser = request.getSession().getAttribute("loginUser");
        if(loginUser==null ){ //没有登陆
            request.setAttribute("msg","没有权限，请先登录");
            request.getRequestDispatcher("./index.html").forward(request,response);
            return false;
        }else {
            return  true;
        }
    }
}

4：编写LoginController类

package com.example.springbootweb.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.thymeleaf.util.StringUtils;

import javax.servlet.http.HttpSession;

/**
 * @author ${范涛之}
 * @Description
 * @create 2021-09-19 14:00
 */
@Controller
public class LoginController {

    @RequestMapping("/user/login")
    public  String login(
            @RequestParam("username") String username,
            @RequestParam("password") String password,
            Model model, HttpSession session){

        //具体业务
        if (!StringUtils.isEmpty(username) && "123456".equals(password)){
            session.setAttribute("loginUser",username);

            return "redirect:/main.html";
        }
        //告诉用户登陆失败了
        else {
            model.addAttribute("msg","用户名或密码错误");
            return "index";

        }

    }
}

5：在MyMvcConfig中配置需要拦截的东西

package com.example.springbootweb.config;

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

/**
 * @author ${范涛之}
 * @Description
 * @create 2021-09-19 10:16
 */
@Configuration
public class MyMvcConfig implements WebMvcConfigurer {

    // 添加视图控制
    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
       registry.addViewController("/").setViewName("index");
       registry.addViewController("/index.html").setViewName("index");
       registry.addViewController("/main.html").setViewName("dashboard");
    }

    //自定义的国际化就生效了
    @Bean
    public LocaleResolver localeResolver(){ return  new MyLocalResolver(); }

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
       registry.addInterceptor(new LoginHandlerInterceptor())
          .addPathPatterns("/**")
          .excludePathPatterns("/index.html","/","/user/login","/css/*","/js/**","/img/**");
    }
}