树迭代循环 java8 用lambda表达式

场景 同一个表 父和子 共存 ParentId 字段使用 一般用于 菜单或者省市区 使用

直接上代码 实体类 不提供 详解 懂得自然懂：

    public CommonResult<List<GoodsCategoryTreeDTO>> goodsCategoryTree() {
        QueryWrapper<ItemCategory> queryWrapper = new QueryWrapper<ItemCategory>().eq("status", 1).orderByAsc("sort");
        List<ItemCategory> categoryEntities = itemCategoryService.list(queryWrapper);
        //1.先找一级分类 categoryEntity.getParentId() == 0L
        //2.查询一级分类下的子类
        List<GoodsCategoryTreeDTO> levelCategory = categoryEntities.stream().
                filter(categoryEntity -> categoryEntity.getParentId() == 0L).
//                sorted(Comparator.comparing(ItemCategory::getMenuOrder)).
                //保存当前分类的子分类
                        map(category -> {
                    //当前分类的子分类收集并返回
                    GoodsCategoryTreeDTO categoryTreeRespDTO = new GoodsCategoryTreeDTO();
                    BeanUtils.copyProperties(category, categoryTreeRespDTO);
                    categoryTreeRespDTO.setChildren(listSubMenu(category, categoryEntities));
                    return categoryTreeRespDTO;
                }).collect(Collectors.toList());
        return CommonResult.success(levelCategory);
    }

    public List<GoodsCategoryTreeDTO> listSubMenu(ItemCategory root, List<ItemCategory> all) {
        List<GoodsCategoryTreeDTO> children = all.stream().
                filter(e -> e.getParentId().equals(root.getId())).
                map(categoryEntity -> {
                    //当前分类的子分类收集并返回
                    GoodsCategoryTreeDTO categoryTreeRespDTO = new GoodsCategoryTreeDTO();
                    BeanUtils.copyProperties(categoryEntity, categoryTreeRespDTO);
                    categoryTreeRespDTO.setChildren(listSubMenu(categoryEntity, all));
                    return categoryTreeRespDTO;
                }).collect(Collectors.toList());
        return children;
    }