使用HutoolUtil工具包之树结构工具TreeUtil 快速处理数据树形结构数据，很好很强大！

前言

数据库里面有子父级的数据，查询出来是一个平级list集合，想要展示树形的数据结构，需要重新封装一下，所以提供一个通用的方法方便灵活

一、数据准备

CREATE TABLE `content_file_category` (
        `id` bigint(20) NOT NULL AUTO_INCREMENT,
        `name` varchar(255) DEFAULT NULL COMMENT '名称',
        `parent_id` bigint(20) DEFAULT NULL COMMENT '所属分类',
        `order_num` int(11) DEFAULT NULL COMMENT '排序序号',
        `level` int(11) DEFAULT NULL COMMENT '第几分类，从1开始',
        `gmt_create` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间',
        `gmt_modify` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '最近更新时间',
        PRIMARY KEY (`id`),
        KEY `level_idx` (`level`),
        KEY `parent_id_idx` (`parent_id`),
        KEY `name_idx` (`name`)
      ) ENGINE=InnoDB AUTO_INCREMENT=68 DEFAULT CHARSET=utf8 COMMENT='文件分类管理'

方案一：

一般情况下，我们自己写递归代码的方式

(1)获取树形结构数据接口

/**
       * 获取文件分类树形结构
       *
       * @return
       */
      @Override
      public FileCategoryListResponse queryFileCategoryTree(Integer levelDeep) {
      //查询一级分类
       List<FileCategoryDO> fileCategoryLevel1 = this.list(new LambdaQueryWrapper<FileCategoryDO>()
       .eq(FileCategoryDO::getLevel, FileCategoryLevelEnum.LEVEL_1.getCode())
       .orderByAsc(FileCategoryDO::getSort));
      //最终响应实体
       FileCategoryListResponse response = new FileCategoryListResponse();
       List<FileCategoryResponse> fileCategoryResponseList = new ArrayList<FileCategoryResponse>();
      if (!CollectionUtils.isEmpty(fileCategoryLevel1)) {
      for (FileCategoryDO fileCategoryDO : fileCategoryLevel1) {
       FileCategoryResponse fileCategoryResponse = new FileCategoryResponse().setChildren(new ArrayList<>());
       BeanUtils.copyProperties(fileCategoryDO, fileCategoryResponse);
      //循环遍历一级分类并进行递归操作，组装子分类
       getChildrenFileCategory(fileCategoryResponse, levelDeep);
       fileCategoryResponseList.add(fileCategoryResponse);
       }
       }
       response.setList(fileCategoryResponseList);
      return response;
       }
      /**
       * 递归获取下层级的文件分类
       *
       * @param fileCategoryResponse
       */
      private void getChildrenFileCategory(FileCategoryResponse fileCategoryResponse, Integer levelDeep) {
      //获取id
      if (fileCategoryResponse != null) {
       Long id = fileCategoryResponse.getId();
       List<FileCategoryDO> list = this.list(new LambdaQueryWrapper<FileCategoryDO>()
       .eq(FileCategoryDO::getPid, id).le(FileCategoryDO::getLevel, levelDeep)
       .orderByAsc(FileCategoryDO::getSort));
      if (!CollectionUtils.isEmpty(list)) {
       List<FileCategoryResponse> childrens = list.stream().map(x -> {
       FileCategoryResponse dto = new FileCategoryResponse().setChildren(new ArrayList<>());
       BeanUtils.copyProperties(x, dto);
      return dto;
       }).collect(Collectors.toList());
       fileCategoryResponse.getChildren().addAll(childrens);
      for (FileCategoryResponse categoryResponse : childrens) {
       getChildrenFileCategory(categoryResponse, levelDeep);
       }
       }
       }
       }

（2）根据父级id 递归获取子节点id集合

/**
       * 根据文件分类id获取最下级文件分类id
       *
       * @param id
       * @return
       */
      @Override
      public List<Long> recurQueryCatehoryId(Long id) {
       List<FileCategoryResponse> categoryResponses = new CopyOnWriteArrayList<>();
       FileCategoryDO fileCategory = this.getById(id);
      if (ObjectUtil.isNull(fileCategory)) {
      return null;
       }
       FileCategoryResponse fileCategoryResponse = new FileCategoryResponse().setChildren(new ArrayList<>());
       BeanUtils.copyProperties(fileCategory, fileCategoryResponse);
       categoryResponses.add(fileCategoryResponse);
      //递归获取子节点
       getChildrenFileCategory(fileCategoryResponse, FileCategoryLevelEnum.LEVEL_3.getCode());
      //将子节点加入到list
       categoryResponses = joinChildrenCategoryId(fileCategoryResponse, categoryResponses);
      //获取当前文件分类的非1级分类id
       List<Long> idList = categoryResponses.stream().filter(x -> x.getLevel() != null && Integer.parseInt(x.getLevel()) > FileCategoryLevelEnum.LEVEL_1.getCode())
       .map(FileCategoryResponse::getId).collect(Collectors.toList());
      // //根据层级进行分组，key-》层级，value-》每层级的文件分类列表
      // Map> collect = categoryResponses.stream().collect(
      // Collectors.groupingBy(FileCategoryResponse::getLevel));
      // //根据层级key进行倒序，找到key值最大的层级（即最下级分类）
      // List idList = collect.entrySet().stream().sorted((o1, o2) -> o2.getKey().compareTo(o1.getKey())).
      // map(x -> x.getValue().stream().map(FileCategoryResponse::getId).collect(Collectors.toList()))
      // .findFirst().orElseGet(ArrayList::new);
      return idList;
       }
      private List<FileCategoryResponse> joinChildrenCategoryId(FileCategoryResponse fileCategoryResponse, List<FileCategoryResponse> categoryResponses) {
       List<FileCategoryResponse> childrens = fileCategoryResponse.getChildren();
      if (!CollectionUtils.isEmpty(childrens)) {
       categoryResponses.addAll(childrens);
      for (FileCategoryResponse children : childrens) {
       joinChildrenCategoryId(children, categoryResponses);
       }
       }
      return categoryResponses;
       }

方案二：

使用 Hutool的 TreeUtil 工具类

public static void main(String[] args) {
      //模拟的从数据库查询出来的数据
       List<FileCategoryDO> fileCategoryDOS = new ArrayList<>();
      // 构建node列表
       List<TreeNode<String>> nodeList = CollUtil.newArrayList();
       List<TreeNode<Long>> collect = fileCategoryDOS.stream().map(fileCategoryDO -> {
       Map<String, Object> map = new HashMap<>();
       map.put("level", "2");
       map.put("gmt_create", LocalDateTime.now());
       map.put("gmt_modifier", LocalDateTime.now());
       TreeNode<Long> treeNode = new TreeNode<Long>().setId(fileCategoryDO.getId())
       .setName(fileCategoryDO.getCategoryName())
       .setParentId(Long.parseLong(fileCategoryDO.getPid()))
       .setWeight(fileCategoryDO.getSort())
       .setExtra(map);
      return treeNode;
       }).collect(Collectors.toList());
      //配置
       TreeNodeConfig treeNodeConfig = new TreeNodeConfig();
      // 自定义属性名 都要默认值的
       treeNodeConfig.setWeightKey("orderNum");
       treeNodeConfig.setIdKey("id");
       treeNodeConfig.setChildrenKey("childrenNode");
      // 最大递归深度
       treeNodeConfig.setDeep(3);
      //转换器
       List<Tree<String>> treeNodes = TreeUtil.build(nodeList, "0", treeNodeConfig,
       (treeNode, tree) -> {
       tree.setId(treeNode.getId());
       tree.setParentId(treeNode.getParentId());
       tree.setWeight(treeNode.getWeight());
       tree.setName(treeNode.getName());
      // 扩展属性 ...
       tree.putExtra("level", treeNode.getExtra().getOrDefault("level", 2));
       tree.putExtra("gmt_create", treeNode.getExtra().getOrDefault("gmt_create", null));
       });
       System.out.println(JSON.toJSONString(treeNodes));
       }