//depts：需要组装树的所有数据
@Override
    public List<TreeSelect> buildDeptTreeSelect(List<SysDept> depts)
    {
        List<SysDept> deptTrees = buildDeptTree(depts);
        return deptTrees.stream().map(TreeSelect::new).collect(Collectors.toList());
    }

@Override
    public List<SysDept> buildDeptTree(List<SysDept> depts) {
        List<SysDept> returnList = new ArrayList<>();
        List<Long> tempList = new ArrayList<>();
        for (SysDept dept : depts) {
            tempList.add(dept.getDeptId());//获取所有数据的id
        }
        for (SysDept dept : depts) {
            // 把最高层级的部门节点取出来  dept.getParentId()都是父节点，而唯独最高节点的父节点不在所有的数据id中
            if (!tempList.contains(dept.getParentId())) {
                recursionFn(depts, dept);
                returnList.add(dept);//将组装好的数据放入最终返回结果集合中
            }
        }
        if (returnList.isEmpty()) {
            returnList = depts;
        }
        return returnList;
    }

private void recursionFn(List<SysDept> list, SysDept t) {
        // 得到子节点列表
        List<SysDept> childList = getChildList(list, t);
        t.setChildren(childList);//将当前子集放入到当前的对象集合中
        for (SysDept tChild : childList) {
            if (hasChild(list, tChild)) {//当前对象中有子数据
                recursionFn(list, tChild);//继续构建下面的子节点
            }
        }
    }

/**
     * 判断是否有子节点
     */
    private boolean hasChild(List<SysDept> list, SysDept t) {
        return getChildList(list, t).size() > 0 ? true : false;
    }

/**
     * 得到子节点列表
     */
    private List<SysDept> getChildList(List<SysDept> list, SysDept t) {
        List<SysDept> tlist = new ArrayList<>();
        Iterator<SysDept> it = list.iterator();
        while (it.hasNext()) {
            SysDept n = (SysDept) it.next();
            //如果下个数据的父级id等于当前传过来数据的id，那么就是当前数据下的子节点
            if (StringUtils.isNotNull(n.getParentId()) && n.getParentId().longValue() == t.getDeptId().longValue()) {
                tlist.add(n);
            }
        }
        return tlist;
    }

此代码是搬运若依系统的

2、另一种方式

//创建一个方法调用
List<Department> departmentVOList = makeDepartmentTree(departmentList, 0L);

public List<Department> makeDepartmentTree(List<Department> departmentList,Long pid) {
        List<Department> objects = new ArrayList<>();//返回最终组织的结果树
        if (CollectionUtils.isEmpty(departmentList)){
            return objects;
        }
        for (Department department : departmentList) {
            if (department.getPid() != null && department.getPid() == pid){//首先传输进来的是顶级节点的pid，所以先判断哪些部门是顶级部门
                //走到这说明找到了下级节点，所以再循环找出下级节点的下级节点，以此类推
                List<Department> departmentVOList = makeDepartmentTree(departmentList, department.getId());
                department.setChildren(departmentVOList);//最后每层找完以后分次弹出数据，然后将数据设置到子节点的集合中
                objects.add(department);
            }
        }
        return objects;
    }