mybatis多對多查詢出現的java.lang.UnsupportedOperationException異常解決方案

在用mybatis多對多查詢時報了一個錯誤，java.lang.UnsupportedOperationException；後來仔細看了一下日誌，提示“處理結果集錯誤”。sql文件如下：

    <resultMap id="dtoList" type="ResourceDTO" autoMapping="true">
    <id column="id1" property="id" ></id>
    <result column="name1" property="name" ></result>
    <result column="pid1" property="pid" ></result>
    <collection property="resourceList" javaType="ResourceDTO" ofType="List" autoMapping="true">
        <id column="id2" property="id" ></id>
        <result column="name2" property="name" ></result>
        <result column="pid2" property="pid" ></result>
        <collection property="resourceList" javaType="ResourceDTO" ofType="List"
                    autoMapping="true">
            <id column="id3" property="id" ></id>
            <result column="name3" property="name" ></result>
            <result column="pid3" property="pid" ></result>
        </collection>
    </collection>
</resultMap>

<select id="selectlist" resultMap="dtoList">
    SELECT
    v1.id as id1,
	v1.name as name1,
	v1.pid as pid1,
	v2.id as id2 ,
	v2.name as name2,
	v2.pid as pid2,
	v3.id as id3,
	v3.name as name3,
	v3.pid as pid3
  FROM
	resource as v1
	left join  resource as v2 on  v2.pid = v1.id
	left join  resource as v3 on v3.pid = v2.id
where v1.pid = 0
</select>

於是立馬想到應該是mysql數據庫的字段類型與java字段類型不匹配，於是做了如下修改：

<resultMap id="dtoList" type="ResourceDTO" autoMapping="true">
    <id column="id1" property="id" jdbcType="BIGINT"></id>
    <result column="name1" property="name" jdbcType="VARCHAR"></result>
    <result column="pid1" property="pid" jdbcType="BIGINT"></result>
    <collection property="resourceList" javaType="ResourceDTO" ofType="List" autoMapping="true">
        <id column="id2" property="id" jdbcType="BIGINT"></id>
        <result column="name2" property="name" jdbcType="VARCHAR"></result>
        <result column="pid2" property="pid" jdbcType="BIGINT"></result>
        <collection property="resourceList" javaType="ResourceDTO" ofType="List"
                    autoMapping="true">
            <id column="id3" property="id" jdbcType="BIGINT"></id>
            <result column="name3" property="name" jdbcType="VARCHAR"></result>
            <result column="pid3" property="pid" jdbcType="BIGINT"></result>
        </collection>
    </collection>
</resultMap>

<select id="selectlist" resultMap="dtoList">
    SELECT
    v1.id as id1,
	v1.name as name1,
	v1.pid as pid1,
	v2.id as id2 ,
	v2.name as name2,
	v2.pid as pid2,
	v3.id as id3,
	v3.name as name3,
	v3.pid as pid3
  FROM
	resource as v1
	left join  resource as v2 on  v2.pid = v1.id
	left join  resource as v3 on v3.pid = v2.id
where v1.pid = 0
</select>

執行代碼，結果還是同樣的錯誤，後來又仔細檢查了sql，原來是把javaType 和 ofType的類型搞混了，修改之後，執行成功：

<resultMap id="dtoList" type="ResourceDTO" autoMapping="true">
    <id column="id1" property="id" jdbcType="BIGINT"></id>
    <result column="name1" property="name" jdbcType="VARCHAR"></result>
    <result column="pid1" property="pid" jdbcType="BIGINT"></result>
    <collection property="ResourceDTOList" javaType="java.util.List" ofType="ResourceDTO" autoMapping="true">
        <id column="id2" property="id" jdbcType="BIGINT"></id>
        <result column="name2" property="name" jdbcType="VARCHAR"></result>
        <result column="pid2" property="pid" jdbcType="BIGINT"></result>
        <collection property="ResourceDTOList" javaType="java.util.List" ofType="ResourceDTO"
                    autoMapping="true">
            <id column="id3" property="id" jdbcType="BIGINT"></id>
            <result column="name3" property="name" jdbcType="VARCHAR"></result>
            <result column="pid3" property="pid" jdbcType="BIGINT"></result>
        </collection>
    </collection>
</resultMap>

<select id="selectlist" resultMap="dtoList">
    SELECT
    v1.id as id1,
	v1.name as name1,
	v1.pid as pid1,
	v2.id as id2 ,
	v2.name as name2,
	v2.pid as pid2,
	v3.id as id3,
	v3.name as name3,
	v3.pid as pid3
  FROM
	resource as v1
	left join  resource as v2 on  v2.pid = v1.id
	left join  resource as v3 on v3.pid = v2.id
where v1.pid = 0
</select>