根据根节点查询所有子节点

package com.atguigu.gulimall.product.service.impl;

import com.sun.org.apache.bcel.internal.generic.RETURN;
import org.springframework.stereotype.Service;

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.core.metadata.IPage;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.atguigu.common.utils.PageUtils;
import com.atguigu.common.utils.Query;

import com.atguigu.gulimall.product.dao.CategoryDao;
import com.atguigu.gulimall.product.entity.CategoryEntity;
import com.atguigu.gulimall.product.service.CategoryService;


@Service("categoryService")
public class CategoryServiceImpl extends ServiceImpl<CategoryDao, CategoryEntity> implements CategoryService {

    @Override
    public PageUtils queryPage(Map<String, Object> params) {
        IPage<CategoryEntity> page = this.page(
                new Query<CategoryEntity>().getPage(params),
                new QueryWrapper<CategoryEntity>()
        );

        return new PageUtils(page);
    }

    @Override
    public List<CategoryEntity> listWithTree() {
        List<CategoryEntity> entities = baseMapper.selectList(null);
        //找到所有一级分类
        List<CategoryEntity> level1Menus = entities.stream().filter((categoryEntity -> {
            return
                    categoryEntity.getParentCid() == 0;
        }
        )).map((menu)->{
            menu.setChildren(getChildrens(menu,entities));
            return menu;
        }).sorted((menu1,menu2)->{
            return menu1.getSort()-menu2.getSort();
        }).collect(Collectors.toList());
        return level1Menus;
    }

    //递归查找所有菜单的子菜单
    private List<CategoryEntity> getChildrens(CategoryEntity root,List<CategoryEntity> all){
        List<CategoryEntity> children = all.stream().filter((categoryEntity -> {
            return categoryEntity.getParentCid() == root.getCatId();
        })).map((categoryEntity -> {
            categoryEntity.setChildren(getChildrens(categoryEntity,all));
            return categoryEntity;
        })).sorted((menu1,menu2)->{
            return (menu1.getSort()==null?0:menu1.getSort())-(menu2.getSort()==null?0:menu2.getSort());
        }).collect(Collectors.toList());
        return children;
    }

}