使用过 mybatis 框架的小伙伴们都知道，mybatis 是个半 orm 框架，通过写 mapper 接口就能自动实现数据库的增删改查，但是对其中的原理一知半解，接下来就让我们深入框架的底层一探究竟
首先引入 mybatis 的依赖，在 resources 目录下创建 mybatis 核心配置文件 mybatis-config.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 环境、事务工厂、数据源 -->
<environments default="dev">
<environment id="dev">
<transactionManager type="JDBC"/>
<dataSource type="UNPOOLED">
<property name="driver" value="org.apache.derby.jdbc.EmbeddedDriver"/>
<property name="url" value="jdbc:derby:db-user;create=true"/>
</dataSource>
</environment>
</environments>
<!-- 指定 mapper 接口-->
<mappers>
<mapper class="com.myboy.demo.mapper.user.UserMapper"/>
</mappers>
</configuration>在 com.myboy.demo.mapper.user 包下新建一个接口 UserMapper
public interface UserMapper {
UserEntity getById(Long id);
void insertOne(@Param("id") Long id, @Param("name") String name, @Param("json") List<String> json);
}在 resources 的 com.myboy.demo.mapper.user 包下创建 UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.myboy.demo.mapper.user.UserMapper">
<select id="getById" resultType="com.myboy.demo.db.entity.UserEntity">
select * from demo_user where id = #{id}
</select>
<insert id="insertOne">
insert into demo_user (id, name, json) values (#{id}, #{name}, #{json})
</insert>
</mapper>创建 main 方法测试
try(InputStream in = Resources.getResourceAsStream("com/myboy/demo/sqlsession/mybatis-config.xml")){
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
sqlSession = sqlSessionFactory.openSession();
# 拿到代理类对象
UserMapper mapper = sqlSession.getMapper(UserMapper.class);
# 执行方法
UserEntity userEntity = mapper.getById(2L);
System.out.println(userEntity);
sqlSession.close();
}catch (Exception e){
e.printStackTrace();
}
