【API要返回一棵树的结构】数据库表结构是平铺的数据，但是api要实现树状结构展示。api实现一棵树的结构，如何实现呢，递归？如何递归呢

数据库中的数据是平铺的，一行行的，但是api要查询出来的数据要求是一棵树的结构，

怎么把平铺的数据转换成树状结构呢？

public List<CarbonRepo> findCarbonRepo(Integer type){// 1. 先查出所有数据。 baseFindList 方法就是查询数据库，返回一个list对象、CarbonRepo 就是数据库中某张表的数据实体List<CarbonRepo> list = this.baseFindList(new CarbonRepo().setType(type).setActiveFlag(true));List<CarbonRepo> collect = list.stream()// 2. 找出所有顶级（规定 2位code 为顶级）.filter(o -> o.getCode().length() == 2)// 3.给当前父级的 childList 设置子.peek(o -> {o.setChildList(getChildList(o, list));o.setKey(o.getId());})// 4.收集.collect(Collectors.toList());return  collect;}

// 通过递归的方式设置每个对象下的子属性。数据库中表的设计是通过code，parent// 根据当前父类 找出子类， 并通过递归找出子类的子类private List<CarbonRepo> getChildList(CarbonRepo carbonRepo, List<CarbonRepo> list) {return list.stream()//筛选出父节点code == parentCode 的所有对象 => list.filter(o -> StringUtil.equals(carbonRepo.getCode(), o.getParentCode())).peek(o -> {o.setChildList(getChildList(o, list));o.setKey(o.getId());}).collect(Collectors.toList());}

数据表结构：

CREATE TABLE `data_carbon_repo` (`id` int(11) NOT NULL AUTO_INCREMENT COMMENT 'id',`code` varchar(32) NOT NULL COMMENT '编码',`name` varchar(32) NOT NULL COMMENT '名称',`parent_code` varchar(32) NOT NULL COMMENT '父编码',`type` tinyint(4) NOT NULL DEFAULT '0' COMMENT '不同用途区分',`active_flag` tinyint(4) NOT NULL DEFAULT '1' COMMENT '删除标识 1: 未删除 0:已删除',`creator` bigint(20) DEFAULT NULL COMMENT '创建人id',`modifier` bigint(20) DEFAULT NULL COMMENT '修改人id',`create_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',`modify_time` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '修改时间',PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=344 DEFAULT CHARSET=utf8 COMMENT='材料库配置表'

api返回的数据：

{"code": 100,"message": "成功","data": [{"id": 279,"code": "01","name": "国标数据","parentCode": "0","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [{"id": 280,"code": "0101","name": "材料碳排放计算标准","parentCode": "01","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [{"id": 281,"code": "010101","name": "水泥混凝土类","parentCode": "0101","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 281},{"id": 282,"code": "010102","name": "建材制品类","parentCode": "0101","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 282},{"id": 283,"code": "010103","name": "钢铁金属类","parentCode": "0101","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 283},{"id": 284,"code": "010104","name": "玻璃及门窗类","parentCode": "0101","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 284},{"id": 285,"code": "010105","name": "其他","parentCode": "0101","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 285}],"key": 280}],"key": 279},{"id": 286,"code": "02","name": "省标数据","parentCode": "0","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [{"id": 287,"code": "0201","name": "江苏省民用建筑碳排放规则（征求意见稿）","parentCode": "02","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [{"id": 288,"code": "020101","name": "水泥及其制品类","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 288},{"id": 289,"code": "020102","name": "地方材料及建材制品类","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 289},{"id": 290,"code": "020103","name": "黑色及有色金属类","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 290},{"id": 291,"code": "020104","name": "玻璃及门窗","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 291},{"id": 292,"code": "020105","name": "化学制品","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 292},{"id": 293,"code": "020106","name": "自来水","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 293},{"id": 294,"code": "020107","name": "装饰面层","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 294},{"id": 295,"code": "020108","name": "油漆、涂料类","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 295},{"id": 296,"code": "020109","name": "预制构件","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 296},{"id": 297,"code": "020110","name": "环保建材","parentCode": "0201","type": 2,"activeFlag": 1,"creator": null,"modifier": null,"createTime": "2023-08-18 16:40:46","modifyTime": "2023-08-18 16:40:46","childList": [],"key": 297}],"key": 287}                 ],"key": 286}         ],"success": true
}