简单树结构生成

实体：

@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;

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

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


}

//subject树结构VO
@Data
public class Subject {

    private String id;
    private String title;

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

实现：

@Override
public List<Subject> getAllSubject() {
    List<Subject> subjects = new ArrayList<>();

    //查询所有数据
    List<EduSubject> all = baseMapper.selectList(null);

    //查询所有的一级区域
    QueryWrapper<EduSubject> wrapper = new QueryWrapper<>();
    wrapper.eq("parent_id", 0);
    List<EduSubject> oneEduSubjectList = baseMapper.selectList(wrapper);

    for (EduSubject eduSubject : oneEduSubjectList) {
        Subject subject = new Subject();
        BeanUtils.copyProperties(eduSubject, subject);
        //查询子节点
        List<Subject> children = findChildrens(eduSubject.getId(), all);
        subject.setChildren(children);

        subjects.add(subject);
    }
    return subjects;
}

public List<Subject> findChildrens(String id, List<EduSubject> all) {
    List<Subject> childList = new ArrayList<>();
    if (id != null && all != null) {
        for (EduSubject eduSubject : all) {
            if (Objects.equals(eduSubject.getParentId(), id)) {
                Subject subject1 = new Subject();
                BeanUtils.copyProperties(eduSubject, subject1);
                subject1.setChildren(findChildrens(subject1.getId(), all));
                childList.add(subject1);
            }
        }
    }
    return childList;
}

 可以改为Lambda表达式的写法。