<settings>
    <setting name="logImpl" value="STDOUT_LOGGING" />  <!-- 打印日志到控制臺(tái)上 -->
    <setting name="lazyLoadingEnabled" value="true"/>   
    <setting name="aggressiveLazyLoading" value="false"/>   <!-- false才會(huì)按需加載，不開啟調(diào)用所有的對象 -->
</settings>

public class UserDO {
  private Integer userId;
  private String username;
  private String password;
  private String nickname;
  private List<PermitDO> permitDOList;
  public UserDO() {}
}

<resultMap id="BaseMap" type="org.apache.ibatis.study.entity.UserDO">
    <id column="user_id" jdbcType="INTEGER" property="userId" />
    <result column="username" jdbcType="VARCHAR" property="username" />
    <result column="password" jdbcType="VARCHAR" property="password" />
    <result column="nickname" jdbcType="VARCHAR" property="nickname"/>
    <collection property="permitDOList" column="user_id" select="getPermitsByUserId"
     fetchType="lazy">
    </collection>
</resultMap>
  <resultMap id="PermitBaseMap" type="org.apache.ibatis.study.entity.PermitDO">
    <id column="id" jdbcType="INTEGER" property="id"/>
    <result column="code" jdbcType="VARCHAR" property="code"/>
    <result column="name" jdbcType="VARCHAR" property="name"/>
    <result column="type" jdbcType="TINYINT" property="type"/>
    <result column="pid" jdbcType="INTEGER" property="pid"/>
  </resultMap>
   <select id="getByUserId2" resultMap="BaseMap">
    select * from user
    where user_id = #{userId}
  </select>
  <select id="getPermitsByUserId" resultMap="PermitBaseMap">
    select p.*
    from user_permit up
    inner join permit p on up.permit_id = p.id
    where up.user_id = #{userId}
  </select>

public class Test {
  public static void main(String[] args) throws IOException {
    try (InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml")) {
      // 構(gòu)建session工廠 DefaultSqlSessionFactory
      SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
      SqlSession sqlSession = sqlSessionFactory.openSession();
      UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
      UserDO userDO = userMapper.getByUserId2(1);
      System.out.println(userDO);
    }
  }
}