springboot 实现tree菜单结构（通过递归的方法）

本文链接：https://blog.youkuaiyun.com/weixin_45172119/article/details/128174704

数据库结构

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返回的数据结构

在这里插入图片描述
children表示下级的菜单

新建一个返回接口类

package com.atguigu.eduservice.entity.subject;

import com.atguigu.eduservice.entity.EduSubject;
import lombok.Data;

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

@Data
public class OtherSubject extends EduSubject {

    private List<OtherSubject> children = new ArrayList<>();
}

实体类

package com.atguigu.eduservice.entity;

import com.baomidou.mybatisplus.annotation.FieldFill;
import com.baomidou.mybatisplus.annotation.IdType;
import java.util.Date;

import com.baomidou.mybatisplus.annotation.TableField;
import com.baomidou.mybatisplus.annotation.TableId;
import java.io.Serializable;
import io.swagger.annotations.ApiModel;
import io.swagger.annotations.ApiModelProperty;
import lombok.Data;
import lombok.EqualsAndHashCode;
import lombok.experimental.Accessors;

/**
 * <p>
 * 课程科目
 * </p>
 *
 * @author testjava
 * @since 2022-11-29
 */
@Data
@EqualsAndHashCode(callSuper = false)
@Accessors(chain = true)
@ApiModel(value="EduSubject对象", description="课程科目")
public class EduSubject implements Serializable {

    private static final long serialVersionUID = 1L;

    @ApiModelProperty(value = "课程类别ID")
    @TableId(value = "id", type = IdType.ID_WORKER_STR)
    private String id;

    @ApiModelProperty(value = "类别名称")
    private String title;

    @ApiModelProperty(value = "父ID")
    private String parentId;

    @ApiModelProperty(value = "排序字段")
    private Integer sort;

    @TableField(fill = FieldFill.INSERT)
    @ApiModelProperty(value = "创建时间")
    private Date gmtCreate;

    @TableField(fill = FieldFill.INSERT_UPDATE)
    @ApiModelProperty(value = "更新时间")
    private Date gmtModified;


}

控制器新增接口

@GetMapping("getAllSubject")
    public R getList() {
        List<OtherSubject> list = eduSubjectService.getAllSubject();
        return R.ok().data("data", list);
    }

新增service实现类方法getAllSubject （service接口也要新增这个方法）
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 @Override

  public List<OtherSubject> getAllSubject() {

    List<EduSubject> list = baseMapper.selectList(null);

    List<OtherSubject> allList = new ArrayList<>();

    allList = list.stream().map(info->{

      OtherSubject otherSubject = new OtherSubject();

      BeanUtils.copyProperties(info, otherSubject);

      return  otherSubject;

    }).collect(Collectors.toList());

    for (OtherSubject subject : allList) {

      subject.setChildren(this.handleList(subject.getId(), allList));

    }

    return allList;

  }

分析：

获取所有菜单列表
将菜单列表转化为需要返回的类型列表（通过stream 方式）
通过递归的方法处理下级菜单

private List<OtherSubject> handleList(String id, List<OtherSubject> list) {
        List<OtherSubject> childMenus = new ArrayList<>();
        for (OtherSubject child : list) {
            if(child.getParentId().equals(id)){
                childMenus.add(child);
            }
        }

        for (OtherSubject childMenu : childMenus) {
            childMenu.setChildren(handleList(childMenu.getId(), list));
        }

       if(childMenus.size() == 0){
           return null;
       }else{
           return  childMenus;