首先定义VO(value object) 值对象

	通常用于业务层之间的数据传递，和PO一样也是仅仅包含数据而已。但应是抽象出的业务对象,可以和表对应,也可以不,这根据业务的需要.个人觉得同DTO(数据传输对象),在web上传递。
	
/**
 * @author QiuQiu&LL
 * @create 2021-07-10  18:20
 * @Description:
 */
@Data
public class SubjectVo implements Serializable {

    private String id;
    private String title;
    private Integer sort;
	// 存放子节点
    private List<SubjectVo> children = new ArrayList<>();
}

Controller

// 展示列表数据
@ApiOperation("嵌套数据列表")
    @PostMapping("/nested-list")
    public R nestedList() {
        List<SubjectVo> subjectVoList = subjectService.nestList();
        return R.ok().data("items", subjectVoList);
    }

Service

List<SubjectVo> nestList();

ServiceImpl

@Override
    public List<SubjectVo> nestList() {
        return baseMapper.selectNestedListByParentId("0");
    }

Dao

/**
     * 获取树形结构数据
     * @param parentId
     * @return
     */
    List<SubjectVo> selectNestedListByParentId(String parentId);

<resultMap id="nestedSubject" type="com.qbb.zxjy.service.edu.entity.vo.SubjectVo">
        <id property="id" column="id"/>
        <result property="title" column="title"/>
        <result property="sort" column="sort"/>
        <collection property="children"
                    column="id"
                    select="selectNestedListByParentId"
                    ofType="com.qbb.zxjy.service.edu.entity.vo.SubjectVo"/>
    </resultMap>

    <select id="selectNestedListByParentId" resultMap="nestedSubject">
        select id, sort, title from edu_subject where parent_id = #{parentId}
    </select>

测试

简单树形嵌套列表后端实现