1.首先在pom.xml文件引入数据库和mybatis-plus的相关依赖，配置application.yml文件

<!--mybatis-plus的起步依赖-->
<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-spring-boot3-starter</artifactId>
    <version>3.5.14</version>
</dependency>

<!--mysql驱动依赖-->
<dependency>
    <groupId>mysql</groupId>
    <artifactId>mysql-connector-java</artifactId>
    <version>8.0.33</version>
</dependency>
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatis
    username: root
    password: 1234

2.创建实体类pojo，与数据库字段对应

package com.example.demo.pojo;
import lombok.Data;

@Data
public class User {
    private Integer id;
    private String name;
    private Short age;
    private Short gender;
    private String phone;
}

3.写UserMapper，MyBatis-Plus 的BaseMapper接口确实能极大简化数据库操作。它提供了一系列开箱即用的单表 CRUD 方法，让你无需编写繁琐的 SQL 语句或 XML 映射文件。

package com.example.demo.mapper;
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.example.demo.pojo.User;
import org.apache.ibatis.annotations.Mapper;

@Mapper
public interface UserMapper extends BaseMapper<User> {
    public User selectById(Integer id);
}

4.写service接口:UserService

package com.example.demo.service;
import com.example.demo.pojo.User;

public interface UserService {
    public User selectById(Integer id);
}

5.写userservice接口的实现类:UserServiceImpl

package com.example.demo.service.impl;
import com.example.demo.mapper.UserMapper;
import com.example.demo.pojo.User;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public  class UserServiceImpl implements UserService {

    @Autowired
    private UserMapper userMapper;

    @Override
    public User selectById(Integer id) {
        return userMapper.selectById(id);
    }
}

6.写controller层UserController

package com.example.demo.controller;
import com.example.demo.pojo.User;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {

    @Autowired
    private UserService userservice;

    @RequestMapping("ById")
    public User selectById(Integer id){
        return userservice.selectById(id);
    }
}

7.浏览器http://localhost:8080/ById?id=1

8.数据库语句

create database if not exists mybatis;

use mybatis;

create table user(
    id int unsigned primary key auto_increment comment 'ID',
    name varchar(100) comment '姓名',
    age tinyint unsigned comment '年龄',
    gender tinyint unsigned comment '性别, 1:男, 2:女',
    phone varchar(11) comment '手机号'
) comment '用户表';

insert into user(id, name, age, gender, phone) VALUES (null,'白眉鹰王',55,'1','18800000000');
insert into user(id, name, age, gender, phone) VALUES (null,'金毛狮王',45,'1','18800000001');
insert into user(id, name, age, gender, phone) VALUES (null,'青翼蝠王',38,'1','18800000002');
insert into user(id, name, age, gender, phone) VALUES (null,'紫衫龙王',42,'2','18800000003');
insert into user(id, name, age, gender, phone) VALUES (null,'光明左使',37,'1','18800000004');
insert into user(id, name, age, gender, phone) VALUES (null,'光明右使',48,'1','18800000005');