mybatis collection关联的时候，collection里面的sql一直不执行

<select id="findGrade" parameterType="int" resultMap="test">
    select * from grade where id=#{id}
    </select>
<resultMap id="test" type="com.hs.Entity.Grade">
  <collection property="student" javaType="list"
    ofType="com.hs.Entity.Student"
    select="findStudent" column="gradeId">
</collection>
</resultMap>

<select id="findStudent" parameterType="int" resultType="com.hs.Entity.Student">
    selcet * from student where id=#{id}
    </select>
</mapper>

参考：http://cczakai.iteye.com/blog/1276750