 <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.2.2</version>
        </dependency>

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

创建student实体类

package com.aoshensoft.entity;

/**
 * @author summer
 * @date 2022-05-04  15:07
 */
public class Student {
    private Integer id;
    private String name;
    private Integer age;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

创建Mapper接口（第一种方式： @Mapper ）

package com.aoshensoft.mapper;

import com.aoshensoft.entity.Student;
import org.apache.ibatis.annotations.Mapper;
import org.apache.ibatis.annotations.Param;

/**
 * @author summer
 * @date 2022-05-04  15:09
 */
@Mapper
public interface StudentMapper {
//    添加一个根据id查询对象的方法
    Student selectStudentById(@Param("stuid") Integer id);
}

?创建mapper配置文件

<?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.aoshensoft.mapper.StudentMapper">


    <select id="selectStudentById" resultType="com.aoshensoft.entity.Student">
        SELECT id, name, age
        FROM student
        where id = #{stuid}
    </select>
</mapper>

编写Service接口以及其实现类

package com.aoshensoft.service;

import com.aoshensoft.entity.Student;

/**
 * @author summer
 * @date 2022-05-04  15:16
 */
public interface StudentService {
     Student queryStudentById(Integer id);
}

package com.aoshensoft.service.impl;

import com.aoshensoft.entity.Student;
import com.aoshensoft.mapper.StudentMapper;
import com.aoshensoft.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

/**
 * @author summer
 * @date 2022-05-04  15:17
 */
@Service
public class StudentServiceImpl implements StudentService {

    @Autowired
    private StudentMapper studentMapper;

    @Override
    public Student queryStudentById(Integer id) {
        return studentMapper.selectStudentById(id);
    }
}

编写Controller测试

package com.aoshensoft.controller;

import com.aoshensoft.entity.Student;
import com.aoshensoft.service.StudentService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;

/**
 * @author summer
 * @date 2022-05-04  15:19
 */
public class StudentController {

    @Autowired
    private StudentService studentService;

    @RequestMapping("/getStudent")
    @ResponseBody
    public String getStudent(Integer id) {
        Student student = studentService.queryStudentById(id);
        return student.toString();
    }
}

在application.properties配置数据库等信息

server.port=9090
server.servlet.context-path=/orm
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
spring.datasource.username=root
spring.datasource.password=1230
spring.datasource.url=jdbc:mysql://localhost:3306/mybatis_plus?serverTimezone=GMT%2B8&characterEncoding=utf-8&useSSL=false