目录整体结构
数据库表

UserController

package com.example.demo.controller;

import com.example.demo.entity.UserEntity;
import com.example.demo.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class UserController {
    @Autowired
    private UserService userService;
    @RequestMapping("/list")
    public UserEntity hello(int id) {
        return userService.findById(id);
    }
}

UserService

package com.example.demo.service;

import com.example.demo.entity.UserEntity;
import com.example.demo.mapper.UserMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class UserService {
    @Autowired
    private UserMapper userMapper;
    public UserEntity findById(int id){
        return userMapper.findById(id);
    }
}

UserMapper

package com.example.demo.mapper;

import com.example.demo.entity.UserEntity;
import org.apache.ibatis.annotations.Mapper;
import org.springframework.stereotype.Repository;

@Repository
public interface  UserMapper {
    UserEntity findById(int id);
}

UserEntity

package com.example.demo.entity;

public class UserEntity {
    private int id;
    private String name;
    private int age;
    private String desc;
    public int getId () {
      return this.id;
    };
    public void setId (int id) {
        this.id = id;
    };
    public String getName () {
        return this.name;
    };
    public void setName (String name) {
        this.name = name;
    };
    public int getAge () {
        return this.age;
    };
    public void setAge (int age) {
        this.age = age;
    };
    public String getDesc () {
        return this.desc;
    };
    public void setDesc (String desc) {
        this.desc = desc;
    };
}

UserMapper.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.example.demo.mapper.UserMapper">
    <select id="findById" parameterType="int" resultType="com.example.demo.entity.UserEntity">
        select * from test_user where id=#{id};
    </select>
</mapper>

application.yml

server:
  port: 8091
spring:
  datasource:
    driver-class-name: com.mysql.cj.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mysql?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8
    username: root
    password: 123456

mybatis:
  # xml映射文件所在的路径，一般用模糊匹配来指定最终的xml文件
  mapper-locations: classpath:/mapper/*.xml
  configuration:
    #采用驼峰形式将数据表中以‘_’分隔的字段映射到java类的某个属性,比如表字段user_name可以映射为类里面的userName属性
    map-underscore-to-camel-case: true

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.2.1</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.example</groupId>
    <artifactId>demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>demo</name>
    <description>demo</description>
    <properties>
        <java.version>21</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>6.1.2</version>
        </dependency>

        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.23</version>
        </dependency>

        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>3.0.3</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

DemoApplication

package com.example.demo;

import org.mybatis.spring.annotation.MapperScan;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
@MapperScan("com.example.demo.mapper")
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }

}