package deep.mapper;

import deep.pojo.Account;

public interface UserMapper {

    //遵循四个原则
    //接口方法名 == Account.xml 中的 id名
    //返回值类型 与 Mapper.xml文件中的返回值类型要一致
    //方法的入参类型要与Mapper.xml文件中入参的类型要一致
    //命名空间绑定此接口（Account.xml 中的 mapper 中的 namespace = “deep.mapper.UserMapper”）
    public Account findUserById(Integer id);
}

<mapper namespace="deep.mapper.UserMapper">
    <select id="findUserById" parameterType="Integer" resultType="deep.pojo.Account">
        select * from account where id = #{v}
    </select>
    
        ....
</mapper>    

package deep.junit;

import java.io.InputStream;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
import org.junit.Test;

import deep.mapper.UserMapper;
import deep.pojo.Account;

public class MyBatisMapperTest {

    @Test
    public void testMapper() throws Exception {
        //加载核心配置文件
        InputStream in = Resources.getResourceAsStream("SqlMapConfig.xml");
        
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(in);
        SqlSession sqlSession = sqlSessionFactory.openSession();
        
        //SqlSession帮我生成一个实现类(给接口)
        UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
        
        Account account = userMapper.findUserById(27);
        System.out.println(account);
    }
}