2021-09-03（java最简单的递归树，单表树查询）

 private List findTree(Long pid, List jgList) {
        List treeNodes = new ArrayList<>();
        for (JgCategory category : jgList) {
            //如果夫级null 就从夫级开始遍历
            if (pid == null && 0L == category.getParentId()) {
                this.treeNod(jgCategoryList, treeNodes, category);
                continue;
            }
            if (pid != null) {
                if (pid.equals(category.getParentId())) {
                    this.treeNod(jgCategoryList, treeNodes, category);
                }
            }
        }
        return treeNodes;
    }

    
    private void treeNod(List jgList, List treeNodes, JgCategory category) {
        JgCategoryTreeResponse node = new JgCategoryTreeResponse();
        node.setSearchCode(category.getSearchCode());
        node.setCode(category.getCode());
        node.setName(category.getName());
        treeNodes.add(node);
        node.setChildList(findTree(category.getId(), jgCategoryList));
    }

@Data
public class JgTreeResponse {

    @ApiModelProperty("节点ID")
    private Long id;

    @ApiModelProperty("名称")
    private String name;

    @ApiModelProperty("编码")
    private String code;

    @ApiModelProperty("搜索码")
    private String searchCode;

    @ApiModelProperty("父节点ID")
    private Long parentId;

    @ApiModelProperty("子级集合")
    private List childList;
}

返给前端就可以

   public Result> selectTree(long userId) {
        //查询全部并返回一个list
        super.select(new Jg());
        //调用递归方法
        List tree = this.findTree(null, jgCategoryList);
        return Result.success(tree);
    }

简单干活，如果不懂你就多看看，debug看看树的运行调用逻辑