java生成树形结构的算法

@Override
public List listWithTree() {
    // 1 查出所有分类
    List entities = baseMapper.selectList(null);
    // 2 组装成父子的树形结构
    List level1Menus = entities.stream().filter(categoryEntity ->
            categoryEntity.getParentCid().longValue() == 0
    ).map((menu)->{
        menu.setChildren(getChildrens(menu,entities));
        return menu;
    }).sorted((menu1,menu2)->{
        return (menu1.getSort() == null?0:menu1.getSort()) - (menu2.getSort() == null?0:menu2.getSort());
    }).collect(Collectors.toList());
    return level1Menus;
}

// 递归查找所有菜单的子菜单
private List getChildrens(CategoryEntity root, List all) {
    List children = all.stream().filter(categoryEntity -> {
        return categoryEntity.getParentCid().longValue() == root.getCatId().longValue();  // 注意此处应该用longValue()来比较，否则会出先bug，因为parentCid和catId是long类型
    }).map(categoryEntity -> {
        // 1 找到子菜单
        categoryEntity.setChildren(getChildrens(categoryEntity, all));
        return categoryEntity;
    }).sorted((menu1, menu2) -> {
        // 2 菜单的排序
        return (menu1.getSort() == null?0:menu1.getSort()) - (menu2.getSort() == null?0:menu2.getSort());
    }).collect(Collectors.toList());
    return children;
}