<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.76</version>
</dependency>

package com.zsh.springboot_web.filter;
import com.itheima.springboot_web.pojo.Result;
import com.itheima.springboot_web.utils.JwtUtils;
import lombok.extern.slf4j.Slf4j;
import com.alibaba.fastjson.JSONObject;
import org.springframework.util.StringUtils;
import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
@WebFilter(urlPatterns = "/*")
@Slf4j
public class LoginFilter implements Filter {
    @Override
    public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain chain) throws IOException, ServletException {
        //前置：强制转换为http协议的请求对象、响应对象 （转换原因：要使用子类中特有方法）
        HttpServletRequest request = (HttpServletRequest) servletRequest;
        HttpServletResponse response = (HttpServletResponse) servletResponse;
        //1.获取请求url
        String url = request.getRequestURL().toString();
        log.info("请求路径：{}", url); //请求路径：http://localhost:8080/login
        //2.判断请求url中是否包含login，如果包含，说明是登录操作，放行
        if(url.contains("/login")){
            chain.doFilter(request, response);//放行请求
            return;//结束当前方法的执行
        }
        //3.获取请求头中的令牌（token）
        String token = request.getHeader("token");
        log.info("从请求头中获取的令牌：{}",token);
        //4.判断令牌是否存在，如果不存在，返回错误结果（未登录）
        if(!StringUtils.hasLength(token)){
            log.info("Token不存在");
            Result responseResult = Result.error("NOT_LOGIN");
            //把Result对象转换为JSON格式字符串 (fastjson是阿里巴巴提供的用于实现对象和json的转换工具类)
            String json = JSONObject.toJSONString(responseResult);
            response.setContentType("application/json;charset=utf-8");
            //响应
            response.getWriter().write(json);
            return;
        }
        //5.解析token，如果解析失败，返回错误结果（未登录）
        try {
            JwtUtils.parseJWT(token);
        }catch (Exception e){
            log.info("令牌解析失败!");
            Result responseResult = Result.error("NOT_LOGIN");
            //把Result对象转换为JSON格式字符串 (fastjson是阿里巴巴提供的用于实现对象和json的转换工具类)
            String json = JSONObject.toJSONString(responseResult);
            response.setContentType("application/json;charset=utf-8");
            //响应
            response.getWriter().write(json);
            return;
        }
        //6.放行
        chain.doFilter(request, response);
    }
}

package com.zsh.springboot_web;
import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.web.servlet.ServletComponentScan;
@SpringBootApplication
@MapperScan("com.itheima.springboot_web.mapper")
@ServletComponentScan
public class SpringbootWebApplication {
    public static void main(String[] args) {
        SpringApplication.run(SpringbootWebApplication.class, args);
    }
}

<dependency>
  <groupId>com.alibaba</groupId>
  <artifactId>fastjson</artifactId>
  <version>1.2.76</version>
</dependency>

package com.zsh.springboot_web.interceptor;
import com.alibaba.fastjson.JSONObject;
import com.itheima.springboot_web.pojo.Result;
import com.itheima.springboot_web.utils.JwtUtils;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.util.StringUtils;
import org.springframework.web.servlet.HandlerInterceptor;
import org.springframework.web.servlet.ModelAndView;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@Component
@Slf4j
public class LoginInterceptor implements HandlerInterceptor {
    /*
    * 重要：
    *   return true;    // 放行
    *          false;   // 不放行
    * */
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        //1.获取请求头中的令牌（token）
        String token = request.getHeader("token");
        log.info("从请求头中获取的令牌：{}",token);
        //2.判断令牌是否存在，如果不存在，返回错误结果（未登录）
        if(!StringUtils.hasLength(token)){
            log.info("Token不存在");
            Result responseResult = Result.error("NOT_LOGIN");
            //把Result对象转换为JSON格式字符串 (fastjson是阿里巴巴提供的用于实现对象和json的转换工具类)
            String json = JSONObject.toJSONString(responseResult);
            response.setContentType("application/json;charset=utf-8");
            //响应
            response.getWriter().write(json);
            return false;
        }
        //3.解析token，如果解析失败，返回错误结果（未登录）
        try {
            JwtUtils.parseJWT(token);
        }catch (Exception e){
            log.info("令牌解析失败!");
            Result responseResult = Result.error("NOT_LOGIN");
            //把Result对象转换为JSON格式字符串 (fastjson是阿里巴巴提供的用于实现对象和json的转换工具类)
            String json = JSONObject.toJSONString(responseResult);
            response.setContentType("application/json;charset=utf-8");
            //响应
            response.getWriter().write(json);
            return false;
        }
        //4.放行
        return true;
    }
}

package com.zsh.springboot_web.config;
import com.itheima.springboot_web.interceptor.DemoInterceptor;
import com.itheima.springboot_web.interceptor.LoginInterceptor;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Configuration
public class WebConfig implements WebMvcConfigurer {
    // 自定义的拦截器对象
/*    @Autowired
    private DemoInterceptor demoInterceptor;*/
    @Autowired
    private LoginInterceptor loginInterceptor;
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // 注册自定义拦截器对象
        registry.addInterceptor(loginInterceptor).addPathPatterns("/**")    // 设置拦截器拦截的请求路径（/**表示拦截所有请求）
                .excludePathPatterns("/login");  // 设置不拦截的请求路径
    }
}