Java 递归查询树是很常见的功能，也有很多写法，小编这里记录stream流递归部门树写法，自从小编用上stream流之后，是爱不释手，的确是个不错的好东西，话不多说，直接上代码

第一步：先创建dept部门表，简单塞点数据

第二步：创建实体类

package com.example.work.entity;

import lombok.Data;

@Data
public class Dept {
    /**
    * 主键id
    */
    private Integer id;

    /**
    * 部门名称
    */
    private String deptName;

    /**
    * 父级id
    */
    private Integer parentId;
}

第三步：创建部门vo对象

package com.example.work.vo;

import com.example.work.entity.Dept;
import lombok.Data;

import java.util.List;

/**
 * @Description: 部门树vo
 * @Author: lyz
 * @CreateTime: 2024-01-11
 */
@Data
public class DeptTreeVO extends Dept {

    private List<DeptTreeVO> childrenList;
}

第三步：编写controller层

package com.example.work.controller;

import com.baomidou.mybatisplus.extension.api.R;
import com.example.work.service.DeptService;
import com.example.work.vo.DeptTreeVO;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * @Description: TODO
 * @Author: lyz
 * @CreateTime: 2024-01-11
 */
@RestController
@RequestMapping("dept")
public class DeptController {

    @Autowired
    DeptService deptService;

    /**
     * @Description: 部门树
     * @return R
     **/
    @GetMapping("/getTreeList")
    public R getTreeList(){
        List<DeptTreeVO> treeVOList = deptService.getTreeList();
        return R.ok(treeVOList);
    }
}

第四步：业务层代码逻辑实现

package com.example.work.service.impl;

import com.baomidou.mybatisplus.core.toolkit.ObjectUtils;
import com.baomidou.mybatisplus.extension.service.impl.ServiceImpl;
import com.example.work.dao.DeptMapper;
import com.example.work.entity.Dept;
import com.example.work.service.DeptService;
import com.example.work.vo.DeptTreeVO;
import org.springframework.beans.BeanUtils;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

/**
 * @Description: TODO
 * @Author: lyz
 * @CreateTime: 2024-01-11
 */
@Service
public class DeptServiceImpl extends ServiceImpl<DeptMapper, Dept> implements DeptService {
    @Override
    public List<DeptTreeVO> getTreeList() {
        List<DeptTreeVO> deptTreeVOList = new ArrayList<>();
        List<Dept> list = this.list();
        list.forEach(dept -> {
            DeptTreeVO deptTreeVO = new DeptTreeVO();
            BeanUtils.copyProperties(dept, deptTreeVO);
            deptTreeVOList.add(deptTreeVO);
        });

        //获取父部门信息
        List<DeptTreeVO> deptTreeVOS = deptTreeVOList.stream().filter(x -> x.getParentId() == 0)
                .map(deptTreeVO -> {
                    deptTreeVO.setChildrenList(getChildrenList(deptTreeVO, deptTreeVOList));
                    return deptTreeVO;
                }).collect(Collectors.toList());

        return deptTreeVOS;
    }

    /**
     * @return List<DeptTreeVO> 子部门信息
     * @Description: 递归查询子部门
     * @param[1] root 父部门
     * @param[2] deptTreeVOList 所有部门
     **/
    private List<DeptTreeVO> getChildrenList(DeptTreeVO root, List<DeptTreeVO> deptTreeVOList) {
        List<DeptTreeVO> childrenList = deptTreeVOList.stream().filter(x -> {
            return Objects.equals(x.getParentId(), root.getId());
        }).map(deptTreeVO -> {
            deptTreeVO.setChildrenList(getChildrenList(deptTreeVO, deptTreeVOList));
            return deptTreeVO;
        }).collect(Collectors.toList());

        return childrenList;
    }
}

第五步：启动程序，并调用接口，结果如下

stream流递归查询部门树，你学会了吗