2, mybatis-简介及快速入门

什么是 MyBatis？

MyBatis 是一款优秀的持久层框架，它支持自定义 SQL、存储过程以及高级映射。MyBatis 免除了几乎所有的 JDBC 代码以及设置参数和获取结果集的工作。MyBatis 可以通过简单的 XML 或注解来配置和映射原始类型、接口和 Java POJO（Plain Old Java Objects，普通老式 Java 对象）为数据库中的记录。

快速入门

mysql数据库测试数据

# 创建数据库
CREATE DATABASE test;

USE `test`;

# 创建表
CREATE TABLE `User` (
  `name` varchar(255) DEFAULT NULL,
  `age` int DEFAULT NULL,
  `sex` int DEFAULT NULL,
  `id` int NOT NULL AUTO_INCREMENT,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=2 DEFAULT CHARSET=utf8;

# 插入测试数据
insert  into `User`(`name`,`age`,`sex`,`id`) values ('xdb',27,1,1);

基于注解

maven依赖

<dependency>
	<groupId>org.mybatis</groupId>
	<artifactId>mybatis</artifactId>
	<version>3.5.5</version>
</dependency>

<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
<dependency>
	<groupId>mysql</groupId>
	<artifactId>mysql-connector-java</artifactId>
	<version>8.0.21</version>
</dependency>

配置文件

mybatis-config-01.xml

<configuration>
	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC"/>
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
				<property name="url" value="jdbc:mysql://172.28.149.239:3306/test?useSSL=false"/>
				<property name="username" value="root"/>
				<property name="password" value="root"/>
			</dataSource>
		</environment>
	</environments>	
</configuration>

mysql6之后的驱动是mysql.cj.jdbc.Driver, MySQL5用的驱动是com.mysql.jdbc.Driver

创建映射对象

User.java

private Integer id;
private String name;
private Integer age;
private Integer sex;
...

编写mapper

UserMapper.java

public interface UserMapper {

	@Select("SELECT id, name, age, sex FROM User WHERE id = #{id}")
	public User selectByid(Integer id);

}

编写测试类

Demo01.java

String resource = "mybatis-config-01.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
sqlSessionFactory.getConfiguration().addMapper(UserMapper.class);
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
	UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
	User user = userMapper.selectByid(1);
	System.out.println(user);
}

xml配置

配置文件

mybatis-config-02.xml

<configuration>
	<environments default="development">
		<environment id="development">
			<transactionManager type="JDBC"/>
			<dataSource type="POOLED">
				<property name="driver" value="com.mysql.cj.jdbc.Driver"/>
				<property name="url" value="jdbc:mysql://172.28.149.239:3306/test?useSSL=false"/>
				<property name="username" value="root"/>
				<property name="password" value="root"/>
			</dataSource>
		</environment>
	</environments>	
	<mappers>
		<mapper resource="mapping/UserMapper.xml"/>
	</mappers>
</configuration>

比上面多了个mappers配置, 通过配置文件加载mapper, 而不需用注解方法的sqlSessionFactory.getConfiguration().addMapper(UserMapper.class); 加载mapper

编写mapper

UserMapper.java

public User selectById(Integer id);

编写mapping

UserMapper.xml, 文件位置与上面的mappers配置中保持一致, namespace与mapper一致, resultType和mapper的返回值类型一致, id和mapper.java中的方法一致

<mapper namespace="top.itkaoti.example02.mapper.UserMapper">
	<select id="selectById" resultType="top.itkaoti.example01.po.User">
    select * from User where id = #{id}
	</select>
</mapper>

测试类

String resource = "mybatis-config-02.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
try (SqlSession sqlSession = sqlSessionFactory.openSession()) {
	UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
	User user = userMapper.selectById(1);
	System.out.println(user);
}

重要概念

SqlSessionFactoryBuilder: 用来创建了 SqlSessionFactory的实例, 一旦创建完成就可以释放。

SqlSessionFactory: 工厂类一般都是单例, 一旦被创建就应该在应用的运行期间一直存在

SqlSession: 每个线程都应该有它自己的 SqlSession 实例。SqlSession 的实例不是线程安全的, 每次操作后都应该关闭

项目地址

mybatis官方文档