1.概述

Mybatis是一个用Java编写的持久层框架，它使用ORM实现了结果集的封装。

ORM是Object Relational Mapping 对象关系映射。简单来说，就是把数据库表和实体类及实体类的属性对应起来，让开发者操作实体类就实现操作数据库表。

它封装了jdbc操作的很多细节，使开发者只需要关注sql语句本身，而无需关注注册驱动，创建连接等烦杂过程

2.快速入门

2.1 准备工作

①数据准备

/*Table structure for table `user` */
DROP TABLE IF EXISTS `user`;
CREATE TABLE `user` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `username` varchar(50) DEFAULT NULL,
  `age` int(11) DEFAULT NULL,
  `address` varchar(50) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=10 DEFAULT CHARSET=utf8;

/*Data for the table `user` */

insert  into `user`(`id`,`username`,`age`,`address`) values (2,'pdd',25,'上海'),(3,'UZI',19,'上海11'),(4,'RF',19,NULL),(6,'神超',14,'请问2'),(8,'test1',11,'cc'),(9,'test2',12,'cc2');

/*!40101 SET SQL_MODE=@OLD_SQL_MODE */;
/*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */;
/*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */;
/*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;

②创建SpringBoot工程

添加依赖

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.0</version>
    </parent>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

创建启动类

@SpringBootApplication
public class MybatisApplication {

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

③准备实体类

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

@Data
@AllArgsConstructor
@NoArgsConstructor
public class User {
    private Integer id;
    private String username;
    private Integer age;
    private String address;
}

2.2 整合Mybatis

github: https://github.com/mybatis/spring-boot-starter/

①添加依赖

        <!--mybatis启动器-->
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.2.0</version>
        </dependency>
        <!--mysql驱动-->
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
            <scope>runtime</scope>
        </dependency>

②配置application.yml文件

spring:
  datasource:
    url: jdbc:mysql://localhost:3306/study?characterEncoding=utf-8&serverTimezone=UTC
    username: root
    password: 123456
    driver-class-name: com.mysql.cj.jdbc.Driver
mybatis:
    mapper-locations: classpath:mapper/*Mapper.xml # mapper映射文件路径 mapper文件夹放在resources下面
    type-aliases-package: com.demo.entity   # 配置哪个包下的类有默认的别名

④编写Mapper接口

注意在接口上加上@Mapper 和@Repository 注解

@Repository
@Mapper
public interface UserMapper {
    public List<User> findAll();
}

⑤编写mapper接口对应的xml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.springboot.mapper.UserMapper">
    <select id="findAll" resultType="com.springboot.domain.User">
        select * from user
    </select>
</mapper>

⑥测试

@SpringBootTest(classes = HelloApplication.class)
public class ApplicationTest {

    @Autowired
    UserMapper userMapper;


    @Test
    public void testMapper(){
        System.out.println(userMapper.findAll());
    }
}