配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper
  PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
  "http://mybatis.org/dtd/mybatis-3-mapper.dtd">

<mapper namespace="com.farmplus.agriculture.dao.ProductCategoryDao">
	<resultMap id="menuMap"
		type="com.farmplus.agriculture.dto.ProductCategoryList">
		<id column="product_category_id" property="value" />
		<result column="product_category_name" property="label"/>
		<collection column="product_category_id" property="children"
			ofType="com.farmplus.agriculture.dto.ProductCategoryList" select="getProductCategoryList" />
	</resultMap>	
	<select id="getProductCategoryList" parameterType="java.math.BigInteger"
		resultMap="menuMap">
		SELECT * from product_category where parent_id = #{value}
	</select>
</mapper>  

返回json数据

{
    "code": 200,
    "options": [
        {
            "value": 1,
            "label": "水果",
            "children": [
                {
                    "value": 5,
                    "label": "甜瓜",
                    "children": [
                        {
                            "value": 14,
                            "label": "绿宝甜瓜",
                            "children": []
                        },
                        {
                            "value": 15,
                            "label": "黄金甜瓜",
                            "children": []
                        }
                    ]
                },
                {
                    "value": 6,
                    "label": "西瓜",
                    "children": [
                        {
                            "value": 16,
                            "label": "黑美人西瓜",
                            "children": []
                        },
                        {
                            "value": 17,
                            "label": "甜王西瓜",
                            "children": []
                        }
                    ]
                },
                {
                    "value": 7,
                    "label": "油桃",
                    "children": []
                }
            ]
        },
        {
            "value": 3,
            "label": "蔬菜",
            "children": [
                {
                    "value": 8,
                    "label": "黄瓜",
                    "children": [
                        {
                            "value": 18,
                            "label": "密刺黄瓜",
                            "children": []
                        },
                        {
                            "value": 19,
                            "label": "旱黄瓜",
                            "children": []
                        }
                    ]
                },
                {
                    "value": 9,
                    "label": "土豆",
                    "children": []
                },
                {
                    "value": 10,
                    "label": "西红柿",
                    "children": []
                }
            ]
        },
        {
            "value": 4,
            "label": "水产",
            "children": [
                {
                    "value": 11,
                    "label": "小龙虾",
                    "children": []
                },
                {
                    "value": 12,
                    "label": "螃蟹",
                    "children": [
                        {
                            "value": 20,
                            "label": "花蟹",
                            "children": []
                        },
                        {
                            "value": 21,
                            "label": "关公蟹",
                            "children": []
                        },
                        {
                            "value": 22,
                            "label": "孟加拉蟹",
                            "children": []
                        }
                    ]
                },
                {
                    "value": 13,
                    "label": "生蚝",
                    "children": []
                }
            ]
        }
    ],
    "message": "成功"
}

问题：