需求分析:

 具体返回如下JSON格式数据

含有四个属性列:id 和 username 和photo 和followerCount

第一步:

 首先按照下面文章创建一个模板项目

SpingBoot——SB整合MB的web项目模板_北岭山脚鼠鼠的博客-CSDN博客

 第二步:

使用如下的建表语句在一个数据库中新建一个用户表

CREATE TABLE `users` (
                         `id` int NOT NULL AUTO_INCREMENT,
                         `username` char(20) DEFAULT NULL,
                         `photo` varchar(200) DEFAULT NULL,
                         `followerCount` int DEFAULT NULL,
                         PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci

并在pojo层中新建一个与之对应的实体类Users

package com.example.backbound.pojo;

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

@Data
@AllArgsConstructor
@NoArgsConstructor
public class Users {
    private int id;
    private String username;
    private String photo;
    private int followerCount;
}

第三步:

解决跨域访问的问题:

新建一个config包，在里面新建一个CorsConfig类，填充以下内容，然后在前后端联调时就不会出现跨域访问报错了。

package com.example.backbound.config;

import org.springframework.context.annotation.Configuration;

import javax.servlet.*;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

@Configuration
public class CorsConfig implements Filter {
    @Override
    public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
        HttpServletResponse response = (HttpServletResponse) res;
        HttpServletRequest request = (HttpServletRequest) req;

        String origin = request.getHeader("Origin");
        if(origin!=null) {
            response.setHeader("Access-Control-Allow-Origin", origin);
        }

        String headers = request.getHeader("Access-Control-Request-Headers");
        if(headers!=null) {
            response.setHeader("Access-Control-Allow-Headers", headers);
            response.setHeader("Access-Control-Expose-Headers", headers);
        }

        response.setHeader("Access-Control-Allow-Methods", "*");
        response.setHeader("Access-Control-Max-Age", "3600");
        response.setHeader("Access-Control-Allow-Credentials", "true");

        chain.doFilter(request, response);
    }

    @Override
    public void init(FilterConfig filterConfig) {

    }

    @Override
    public void destroy() {
    }
}

 第四步:

准备三层架构各个类

controller层:

新建一个userlistcontroller

package com.example.backbound.controller.userlist;


import com.example.backbound.pojo.Users;
import com.example.backbound.service.userlist.impl.userlistservice;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

@RestController
@RequestMapping("/userlist/")
public class userlistcontroller {


    @Autowired
    private userlistservice  userlistservice;

    @GetMapping
    public List<Users> getuserlist(){
        List<Users> usersList=userlistservice.getuserlist();
        return usersList;
    }
}

service层：

先新建一个userlistservice接口

package com.example.backbound.service.userlist;

import com.example.backbound.pojo.Users;

import java.util.List;

public interface userlist {
    public List<Users> getuserlist();

}

在新建一个该接口的实现类

package com.example.backbound.service.userlist.impl;

import com.example.backbound.mapper.userlist.UserlistMapper;
import com.example.backbound.pojo.Users;
import com.example.backbound.service.userlist.userlist;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

@Service
public class userlistservice implements userlist {
    @Autowired
    private UserlistMapper userlistMapper;
    @Override
    public List<Users> getuserlist() {
        return userlistMapper.getuserlist();
    }
}

 Mapper层:

实现一个userlistMapper接口如下

package com.example.backbound.mapper.userlist;

import com.example.backbound.pojo.Users;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Select;

import java.util.List;

@Mapper
public interface UserlistMapper {

    @Select("select * from users")
    List<Users> getuserlist();
}

最后项目文件结构如下所示