这里是接上一篇(示例代码中也包含了前面一篇的相关内容)，知道如何连接MySQL数据库之后，实际中，我们多半不会直接用JDBC连接MYSQL数据库，而是使用这里的MyBatis。
MyBatis是一个持久层框架，定义了SQL、存储过程等映射，通过它避免了开发人员自己写数据库相关的代码。接下来是一个示例。

1、依赖配置添加

在connnect/pom.xml文件中添加mybatis依赖，如下：

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.space.mysql</groupId>
    <artifactId>connnect</artifactId>
    <version>1.0-SNAPSHOT</version>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.0.0.RELEASE</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-jdbc</artifactId>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <version>8.0.11</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.2.0</version>
        </dependency>
    </dependencies>

</project>

2、添加在应用配置文件中添加MyBatis相关配置

主要是说明下数据库记录映射的类和mapper配置文件的路径信息。
application.properties：

spring.datasource.username=root
spring.datasource.password=lfqylfqy
spring.datasource.url=jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC&useUnicode=true&characterEncoding=utf-8
spring.datasource.driver-class-name=com.mysql.jdbc.Driver
#mybatis相关配置
#数据库记录映射类所在的包和mapper文件存放的位置
mybatis.type-aliases-package=com.space.mysql.connect.domain
mybatis.mapper-locations=classpath:mybatis/mapper/*.xml

新增一个mapper文件，并在其中定义相关的sql语句。
mybatis/mapper/StudentMapper.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.space.mysql.connect.mapper.StudentMapper">
    <select id="queryStudentList" resultType="com.space.mysql.connect.domain.Student">
        select * from student
    </select>
    <select id="queryStudentById" resultType="com.space.mysql.connect.domain.Student">
        select * from student where id = #{id}
    </select>
    <insert id="addStudent" parameterType="com.space.mysql.connect.domain.Student">
        insert into Student(id, name, age) VALUES (#{id}, #{name}, #{age})
    </insert>
    <update id="updateStudent" parameterType="com.space.mysql.connect.domain.Student">
        update Student set name = #{name}, age = #{age} where id = #{id}
    </update>
    <delete id="deleteStudent" parameterType="int">
        delete from Student where id = #{id}
    </delete>
</mapper>

3、Java代码编写

3.1 新增一个和数据库表中记录对应的java类

这里借用之前的表结构：

$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 51
Server version: 8.0.20 MySQL Community Server - GPL

Copyright (c) 2000, 2020, Oracle and/or its affiliates. All rights reserved.

Oracle is a registered trademark of Oracle Corporation and/or its
affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql> use testdb;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -A

Database changed
mysql> describe student;
+-------+-------------+------+-----+---------+-------+
| Field | Type        | Null | Key | Default | Extra |
+-------+-------------+------+-----+---------+-------+
| id    | int         | NO   | PRI | NULL    |       |
| name  | varchar(30) | YES  |     | NULL    |       |
| age   | varchar(10) | YES  |     | NULL    |       |
+-------+-------------+------+-----+---------+-------+
3 rows in set (0.00 sec)

mysql>

com.space.mysql.connect.domain.Student：

package com.space.mysql.connect.domain;

/**
 * Created by chengxia on 2021/12/11.
 */
public class Student {
    private int id;
    private String name;
    private int age;

    public Student(int id, String name, int age) {
        this.id = id;
        this.name = name;
        this.age = age;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public int getAge() {
        return age;
    }

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

3.2 新增一个Mapper接口对应mapper配置文件

这个接口可以结合配置文件，对应到sql语句。
com.space.mysql.connect.mapper.StudentMapper：

package com.space.mysql.connect.mapper;

import com.space.mysql.connect.domain.Student;
import org.apache.ibatis.annotations.Mapper;

import java.util.List;

/**
 * Created by chengxia on 2021/12/11.
 */
@Mapper
public interface StudentMapper {
    List<Student> queryStudentById(int id);
    List<Student> queryStudentList();
    void addStudent(Student stu);
    void updateStudent(Student stu);
    void deleteStudent(int id);
}

3.3 新增数据库Service类对数据库操作进行包装(调用mapper)

这里将服务多抽象了一层接口。
服务接口类com.space.mysql.connect.service.StudentServiceInterface：

package com.space.mysql.connect.service;

import com.space.mysql.connect.domain.Student;

import java.util.List;

/**
 * Created by chengxia on 2021/12/12.
 */
public interface StudentServiceInterface {
    Student queryStudentById(int id);
    List<Student> queryStudentList();
    void addStudent(Student stu);
    void updateStudent(Student stu);
    void deleteStudent(int id);
}

服务实现类com.space.mysql.connect.service.StudentService：

package com.space.mysql.connect.service;

import com.space.mysql.connect.domain.Student;
import com.space.mysql.connect.mapper.StudentMapper;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.List;

/**
 * Created by chengxia on 2021/12/12.
 */
@Service
public class StudentService implements StudentServiceInterface {
    @Autowired
    private StudentMapper stuMapper;
    @Override
    public Student queryStudentById(int id) {
        List<Student> studentList = stuMapper.queryStudentById(id);
        if(studentList != null && studentList.size() > 0) {
            System.out.println(studentList.get(0));
            return studentList.get(0);
        }else{
            return null;
        }
    }

    @Override
    public List<Student> queryStudentList() {
        List<Student> studentList = stuMapper.queryStudentList();
        for (Student stu: studentList){
            System.out.println(stu);
        }
        return studentList;
    }

    @Override
    public void addStudent(Student stu) {
        stuMapper.addStudent(new Student(stu.getId(), stu.getName(), stu.getAge()));
    }

    @Override
    public void updateStudent(Student stu) {
        stuMapper.updateStudent(new Student(stu.getId(),stu.getName(), stu.getAge()));
    }

    @Override
    public void deleteStudent(int id) {
        stuMapper.deleteStudent(id);
    }
}

3.4 应用启动类中增加mapper等类的扫描包路径

这一步必不可少，不然会报错mapper类的bean找不到。

Consider defining a bean of type 'com.space.mysql.connect.mapper.StudentMapper' in your configuration.

com.space.mysql.connect.main.Application：

package com.space.mysql.connect.main;

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

/**
 * Created by chengxia on 2021/12/7.
 */
@SpringBootApplication
@ComponentScan(basePackages = {"com.space.mysql.connect.controller","com.space.mysql.connect.service"})
@MapperScan(value = "com.space.mysql.connect.mapper")
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

4、写一个测试的controller类

这里简单的写一个controller类，调用前面的service实现和数据库交互。
com.space.mysql.connect.controller.StudentController

package com.space.mysql.connect.controller;

import com.space.mysql.connect.domain.Student;
import com.space.mysql.connect.service.StudentService;
import com.space.mysql.connect.service.StudentServiceInterface;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * Created by chengxia on 2021/12/12.
 */
@RestController
public class StudentController {
    @Autowired
    private StudentServiceInterface stuService;

    @GetMapping("/queryStudentList")
    public List<Student> queryStudentList(){
        List<Student> stuList = stuService.queryStudentList();
        return stuList;
    }

    @GetMapping("/queryStudentById")
    public Student queryStudentById(){
        Student stuTmp = stuService.queryStudentById(2);
        return stuTmp;
    }

    @GetMapping("/addStudent")
    public String addStudent(){
        stuService.addStudent(new Student(3,"Tim", 36));
        return "insert Tim ok, id = 3";
    }

    @GetMapping("/updateStudent")
    public String updateStudent(){
        stuService.updateStudent(new Student(3,"MMPP", 36));
        return "modify paopao into MMPP!";
    }

    @GetMapping("/deleteStudent")
    public String deleteStudent(){
        stuService.deleteStudent(3);
        return "deleted id = 3";
    }
}

到这里，代码就都结束了，最后的目录结构如下图。

image.png

运行之后，浏览器访问如下链接都可以得到预期的输出。

• http://localhost:8080/queryStudentList
• http://localhost:8080/queryStudentById
• http://localhost:8080/addStudent
• http://localhost:8080/updateStudent
• http://localhost:8080/deleteStudent