java之树结构的实现

1.建数据库名为tree

2.写代码

包的层次：

实体类：

package com.gsl.node.entity;

import com.baomidou.mybatisplus.annotation.IdType;
import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import com.baomidou.mybatisplus.annotation.TableName;
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.List;

/**
 * @Author ：Guo Shi Lin
 * @date ： 2020/8/18 13:57
 * @description：菜单树
 * @modified By：
 * @version: 1.0
 */
@Data
@NoArgsConstructor
@AllArgsConstructor
@TableName("tree")
public class Tree {
    @TableId(value = "id", type = IdType.AUTO)
    private Integer id;
    private String name;
    private Integer parentId;
    @TableField(exist = false)
    private List<Tree> children;
} 

数据访问层接口dao：

package com.gsl.node.dao;

import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import com.gsl.node.entity.Tree;
import org.apache.ibatis.annotations.Mapper;

/**
 * @Author ：Guo Shi Lin
 * @date ： 2020/8/18 13:58
 * @description：
 * @modified By：
 * @version: 1.0
 */
@Mapper
public interface TreeDao extends BaseMapper<Tree> {

} 

业务逻辑层接口service：

package com.gsl.node.service;

import com.gsl.node.entity.Tree;

import java.util.List;

/**
 * @Author ：Guo Shi Lin
 * @date ： 2020/8/18 13:58
 * @description：
 * @modified By：
 * @version: 1.0
 */
public interface TreeService {
    /**
     * 查找树
     * @return
     */
    List<Tree> findList();
} 

业务逻辑层实现类impl：

package com.gsl.node.service.impl;

import com.gsl.node.dao.TreeDao;
import com.gsl.node.entity.Tree;
import com.gsl.node.service.TreeService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import java.util.ArrayList;
import java.util.List;

/**
 * @Author ：Guo Shi Lin
 * @date ： 2020/8/18 14:00
 * @description：用的递归实现
 * @modified By：
 * @version: 1.0
 */
@Service
public class TreeServiceImpl implements TreeService {

    @Autowired
    private TreeDao treeDao;

    @Override
    public List<Tree> findList() {
        return treeDao.selectList(null);
    }

    public List<Tree> handleTree() {
        //根节点list
        List<Tree> treeList = new ArrayList<>();
        //从数据库获取所有得数据
        List<Tree> allTree = treeDao.selectList(null);
        if (null != allTree && allTree.size() > 0) {
            allTree.forEach(tree -> {
                if (tree.getParentId() == 0) {
                    treeList.add(tree);
                }
            });

            if (null != treeList && treeList.size() > 0) {
                treeList.forEach(tree -> {
                    //使用递归获取孩子
                    List<Tree> childrenList = getChildren(tree.getId(), allTree);
                    tree.setChildren(childrenList);
                });
            }
        }
        return treeList;
    }

    /**
     * 使用递归获取根节点下面得孩子
     * @param id
     * @param allTree
     * @return
     */
    public List<Tree> getChildren(Integer id, List<Tree> allTree) {
        List<Tree> childrenList = new ArrayList<>();
        allTree.forEach(tree -> {
            if (tree.getParentId().equals(id)) {
                childrenList.add(tree);
            }
        });

        if (null != childrenList && childrenList.size() > 0) {
            childrenList.forEach(tree -> {
                tree.setChildren(getChildren(tree.getId(), allTree));
            });

        } else {
            return null;
        }
        return childrenList;
    }
} 

控制层controller：

package com.gsl.node.controller;

import com.gsl.node.entity.Tree;
import com.gsl.node.service.TreeService;
import com.gsl.node.service.impl.TreeServiceImpl;
import com.gsl.result.ResponseResult;
import io.swagger.annotations.Api;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import java.util.List;

/**
 * @Author ：Guo Shi Lin
 * @date ： 2020/8/19 9:37
 * @description：
 * @modified By：
 * @version: 1.0
 */
@RestController
@Api(tags = "树")
public class TreeController {
    @Autowired
    private TreeServiceImpl treeService;

    @GetMapping("tree")
    public ResponseResult<Tree> tree() {
        return new ResponseResult(200, "成功", treeService.handleTree());
    }
} 

3.测试结果

{
    "code": 200,
    "msg": "成功",
    "data": [
        {
            "id": 1,
            "name": "根节点",
            "parentId": 0,
            "children": [
                {
                    "id": 2,
                    "name": "父节点",
                    "parentId": 1,
                    "children": [
                        {
                            "id": 3,
                            "name": "子节点",
                            "parentId": 2,
                            "children": null
                        },
                        {
                            "id": 4,
                            "name": "子节点-1",
                            "parentId": 2,
                            "children": null
                        }
                    ]
                },
                {
                    "id": 5,
                    "name": "父节点-1",
                    "parentId": 1,
                    "children": null
                }
            ]
        },
        {
            "id": 6,
            "name": "根节点-1",
            "parentId": 0,
            "children": null
        }
    ]
}

本文地址：https://blog.csdn.net/demo_gsl/article/details/108252238