mybatis

mybatis实现原理

mybatis做的事情，首先要通过配置，构建SqlSessionFactory, SqlSessionFactory是构建SqlSession对象的Factory工厂

DataSource dataSource = BlogDataSourceFactory.getBlogDataSource();
TransactionFactory transactionFactory =
  new JdbcTransactionFactory();
Environment environment =
  new Environment("development", transactionFactory, dataSource);
Configuration configuration = new Configuration(environment);
configuration.addMapper(BlogMapper.class);
SqlSessionFactory sqlSessionFactory =
  new SqlSessionFactoryBuilder().build(configuration);

给用户的Mapper接口类创建动态代理，通过SqlSession.getMapper获取对应的Mapper类的Mapper对象， 这个Mapper对象是Mapper接口的动态代理类的对象。

try (SqlSession session = sqlSessionFactory.openSession()) {
  BlogMapper mapper = session.getMapper(BlogMapper.class);
  Blog blog = mapper.selectBlog(101);
}

mybatis需要解析Mapper.xml文件，并且将对应的语句和Mapper接口的方法对应起来，还需要处理ResultMap这类的语法功能。

<mapper namespace="org.mybatis.example.BlogMapper">
  <select id="selectBlog" resultType="Blog">
    select * from Blog where id = #{id}
  </select>
</mapper>

Mapper接口还支持使用注解配置sql语句

public interface BlogMapper {
  @Select("SELECT * FROM blog WHERE id = #{id}")
  Blog selectBlog(int id);
}