Java 树形结构构造器

1. 创建树型结构节点基类

/**
 * Tree基类
 */
public class TreeEntity extends BaseEntity
{
    private static final long serialVersionUID = 1L;

    /** 当前节点ID */
    private int id;

    /** 父节点ID */
    private int parentId;

    /** 显示顺序 */
    private int orderNum;

     /** 子节点列表 */
    private List<TreeEntity> children = new ArrayList<>();
    
}

2. 树型结构构造器

先生成父节点

然后调用buildChildren 递归生成子节点

 public static  List<? extends TreeEntity> buildTree(List<? extends TreeEntity> dataList, int level) {
        List<TreeEntity> parentList = new ArrayList<>();
        x = 0;
        // 生成0级节点
        TreeEntity treeEntity = new TreeEntity();
        treeEntity.setLabel("全部");
        treeEntity.setId(0);
        treeEntity.setOrderNum(1);
        parentList.add(treeEntity);

        buildChildren(parentList, dataList,level);
        return parentList;
    }

3. 子节点递归生成器

 private static void buildChildren(List<? extends TreeEntity> parentList, List<? extends TreeEntity> dataList,int level) {
        if(x<level) {
            x++;
            for (TreeEntity parent : parentList) {
                List<? extends TreeEntity> children = dataList.stream().filter(item -> ((TreeEntity) item).getParentId() == parent.getId())
                        .collect(Collectors.toList());

                parent.setChildren((List<TreeEntity>) children);

                buildChildren(children, dataList, level);
            }
        }

    }

4. 构造器的使用

4.1实体类

@Data
public class DormGroup extends TreeEntity {

    private int id;

    /**
     * 分组名称
     */
    @NotBlank
    private String menuName;
    /**
     * 父分组ID
     */
    @NotNull
    private int parentId;
    /**
     * 父分组名称
     */
    private String parentName;

    /**祖级列表*/
    private String  ancestors;
    /**
     * 显示顺序
     */
    private int orderNum;
    /**
     * 分组状态（0正常 1删除）
     */
    private char status

}

4.2 mapper

<resultMap id="dormGroupResult" type="com.foen.dorm.domain.DormGroup">
        <id property="id" column="id" />
        <result property="menuName" column="menu_name"/>
        <result property="label" column="menu_name"/>
        <result property="parentId" column="parent_id"/>
        <result property="ancestors" column="ancestors"/>
        <result property="parentName" column="parent_name"/>
        <result property="orderNum" column="order_num" />
        <result property="status"   column="status"/>
        <result property="createBy"      column="create_by"      />
        <result property="createTime"    column="create_time"    />
        <result property="updateBy"      column="update_by"      />
        <result property="updateTime"    column="update_time"    />

    </resultMap>

    <sql id="selectDormGroup">

        select
            a.id,
            a.menu_name,
            a.parent_id,
            a.ancestors,
            b.menu_name as parent_name,
            a.order_num,
            a.status,
            a.create_by,
            a.create_time,
            a.update_by,
            a.update_time
        from
            `foen-vue`.dorm_group a
        left join  `foen-vue`.dorm_group  b on  a.parent_id  = b.id

    </sql>

4.3 service中使用

public List<DormGroup> selectList() {
    List<DormGroup> dormGroups = dormGroupMapper.selectDormGroup();
    return (List<DormGroup>) buildTree(dormGroups);

}

查询子分类(含自己)

id	menu_name	parent_id	ancestors	order_num	status
1	洪鼎城	0	0	1	0
2	忠信22	0	0	2	0
3	一号楼	1	0,1	1	0
4	二号楼	1	0,1	2	0
5	三号楼	1	0,1	3	0
6	4号楼	1	0,1	4	0
7	333	0	0	3	0
8	4444	0	0	4	1
9	40001	8	0,8	1	1
10	4000102	9	0,8,9	1	1
11	33301	7	0,7	1	0
12	33302	7	0,7	2	0
13	33303	7	0,7	3	0
14	4441	0	0	4	1
19	33304	7	0,7	4	0

select id from `foen-vue`.dorm_group   where FIND_IN_SET(#{groupId},ancestors) 
union all select #{groupId} as id 

查询父分类id(含自己)

将表中的ancestors字段按逗号分割成行

SELECT
SUBSTRING_INDEX(SUBSTRING_INDEX(a.ancestors,',',b.help_topic_id+1),',',-1) AS id
FROM
mysql.help_topic b
inner join `foen-vue`.dorm_group a
WHERE
b.help_topic_id <![CDATA[< ]]>  LENGTH(a.ancestors)-LENGTH(REPLACE(a.ancestors,',',''))+1
and a.id = #{id}
union all select #{id} AS id