Mybatis当bean里属性名和数据库属性名不一样时如何解决?

pojo里属性名是               数据库里属性名是:
username ;                       user_name
userage ;                        user_age

<select id="selectByExampleWithBLOBs" resultType ="ResultMapWithBLOBs" parameterType="int" >
    select  user_name username,user_age  userage  from user where id = #{a};
</select>

<configuration>
<settings>
<！--开启驼峰命名规则，可以将数据库中的下划线映射为驼峰命名例如：last_name可以自动映射为lastName
-->
<setting name="mapUnderscorgToCamelCase"  value="true"/】
</settings>

<select id="selectByExampleWithBLOBs" resultMap="myMap" parameterType="int" >
    select  user_name username,user_age  userage  from user where id = #{a};
</select>

<resultMap type="com.atguigu.mybatis.entities.Employee"  id="myMap">
  <！--映射主键-->
  <id column="id"property="id"/>
  <！--映射其他列-->
  <result column="user_name" property="username"/>
  <result column=user_age"   property="userage"/>
</resultMap>