有一类数据在数据库表中是一行一行地存储的,一旦查询出来并展示到前端页面,就呈现出“树状”。例如某大公司的部门数据,可分为一级、二级、三级部门等,在前端页面通常以树形展示。如何设计呢?
第一版
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.util.ArrayList;
import java.util.List;
@Data
@AllArgsConstructor
@NoArgsConstructor
public class Node {
/**
* 主键id
*/
private Long id;
/**
* 名称
*/
private String name;
/**
* 关联父id
*/
private Long parentId;
/**
* 当前节点所处层级,通常level在10以内
* 非必须属性
*/
private int level;
/**
* 关联子对象集合
*/
private List<Node> children = new ArrayList<>();
public Node(Long id, String name, Long parentId, int level) {
this.id = id;
this.name = name;
this.parentId = parentId;
this.level = level;
}
}
import org.apache.commons.collections4.CollectionUtils;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;
public class TreeUtil {
/**
* 根据parentId属性,使用递归算法,为每个节点的children属性赋值,实际上,就是生成一棵树
* @param nodeList children属性为null的节点列表,可理解为某数据库表的集合
* @return children属性正确的节点列表,其size()即为一级节点数量
*/
public static List<Node> build(List<Node> nodeList) {
List<Node> res = new ArrayList<>();
for (Node node : nodeList) {
// 如果是父节点
if (node.getParentId() == 0L) {
buildChildren(node, nodeList);
res.add(node);
}
}
return res;
}
/**
* 递归查找某个节点的孩子
* @param node
* @param list
*/
public static void buildChildren(Node node, final List<Node> list) {
// 从list中找到node的孩子
List<Node> children = list.stream().filter(p->p.getParentId().equals(node.getId())).collect(Collectors.toList());
if (!CollectionUtils.isEmpty(children)) {
for (Node child : children) {
// 递归调用,从list中找到孩子的孩子
buildChildren(child, list);
}
node.setChildren(children);
}
}
/**
* 以可读的样式打印部门树,仅用于调试
* @param list
*/
public static void printTree(List<Node> list) {
if (CollectionUtils.isEmpty(list)) {
return;
}
for (Node node : list) {
System.out.println();
int level = node.getLevel();
if (level == 0) {
// 不打印0级
} else if (level == 1) {
System.out.print("" + node.getName());
} else if (level == 2) {
System.out.print(" + " + node.getName());
} else if (level == 3) {
System.out.print(" + " + node.getName());
} else if (level == 4) {
System.out.print(" + " + node.getName());
} else {
throw new IllegalArgumentException("暂时支持到4级");
}
printTree(node.getChildren());
}
}
}
import org.junit.Test;
import java.util.ArrayList;
import java.util.List;
public class ServiceTest {
/**
* 只有一级部门
* +----+--------------+----------+-------+
* | id | name | parentId | level |
* +----+--------------+----------+-------+
* | 1 | 某某集团公司 | 0 | 0 |
* | 2 | 部门1-1 | 1 | 1 |
* | 3 | 部门1-2 | 1 | 1 |
* | 4 | 部门1-3 | 1 | 1 |
* +----+--------------+----------+-------+
*/
@Test
public void test() {
// 模拟从数据库中查询出来的结果集
List<Node> nodes = new ArrayList<>();
nodes.add(new Node(1L,"某某集团公司",0L, 0));
nodes.add(new Node(2L,"部门1-1",1L, 1));
nodes.add(new Node(3L,"部门1-2",1L, 1));
nodes.add(new Node(4L,"部门1-3",1L, 1));
List<Node> list = TreeUtil.build(nodes);
TreeUtil.printTree(list);
}
/**
* +----+--------------+----------+-------+
* | id | name | parentId | level |
* +----+--------------+----------+-------+
* | 1 | 某某集团公司 | 0 | 0 |
* | 2 | 部门1-1 | 1 | 1 |
* | 3 | 部门1-2 | 1 | 1 |
* | 4 | 部门1-3 | 1 | 1 |
* | 5 | 部门2-1 | 2 | 2 |
* | 6 | 部门2-2 | 2 | 2 |
* | 7 | 部门2-3 | 3 | 2 |
* | 8 | 部门2-4 | 3 | 2 |
* | 9 | 部门2-5 | 4 | 2 |
* | 10 | 部门2-6 | 4 | 2 |
* +----+--------------+----------+-------+
*/
@Test
public void test02() {
// 模拟从数据库中查询出来的结果集
List<Node> nodes = new ArrayList<>();
nodes.add(new Node(1L,"某某集团公司",0L, 0));
nodes.add(new Node(2L,"部门1-1",1L, 1));
nodes.add(new Node(3L,"部门1-2",1L, 1));
nodes.add(new Node(4L,"部门1-3",1L, 1));
nodes.add(new Node(5L,"部门2-1",2L, 2));
nodes.add(new Node(6L,"部门2-2",2L, 2));
nodes.add(new Node(7L,"部门2-3",3L, 2));
nodes.add(new Node(8L,"部门2-4",3L, 2));
nodes.add(new Node(9L,"部门2-5",4L, 2));
nodes.add(new Node(10L,"部门2-6",4L, 2));
List<Node> list = TreeUtil.build(nodes);
TreeUtil.printTree(list);
}
/**
* +----+--------------+----------+-------+
* | id | name | parentId | level |
* +----+--------------+----------+-------+
* | 1 | 某某集团公司 | 0 | 0 |
* | 2 | 部门1-1 | 1 | 1 |
* | 3 | 部门1-2 | 1 | 1 |
* | 4 | 部门1-3 | 1 | 1 |
* | 5 | 部门2-1 | 2 | 2 |
* | 6 | 部门2-2 | 2 | 2 |
* | 7 | 部门2-3 | 3 | 2 |
* | 8 | 部门2-4 | 3 | 2 |
* | 9 | 部门2-5 | 4 | 2 |
* | 10 | 部门2-6 | 4 | 2 |
* | 11 | 部门3-1 | 5 | 3 |
* | 12 | 部门3-2 | 5 | 3 |
* | 13 | 部门3-3 | 6 | 3 |
* | 14 | 部门3-4 | 6 | 3 |
* | 15 | 部门3-5 | 7 | 3 |
* | 16 | 部门3-6 | 7 | 3 |
* | 17 | 部门3-7 | 8 | 3 |
* | 18 | 部门3-8 | 8 | 3 |
* | 19 | 部门3-9 | 9 | 3 |
* | 20 | 部门3-10 | 9 | 3 |
* | 21 | 部门3-11 | 10 | 3 |
* | 22 | 部门3-12 | 10 | 3 |
* +----+--------------+----------+-------+
*/
@Test
public void test03() {
// 模拟从数据库中查询出来的结果集
List<Node> nodes = new ArrayList<>();
nodes.add(new Node(1L,"某某集团公司",0L, 0));
nodes.add(new Node(2L,"部门1-1",1L, 1));
nodes.add(new Node(3L,"部门1-2",1L, 1));
nodes.add(new Node(4L,"部门1-3",1L, 1));
nodes.add(new Node(5L,"部门2-1",2L, 2));
nodes.add(new Node(6L,"部门2-2",2L, 2));
nodes.add(new Node(7L,"部门2-3",3L, 2));
nodes.add(new Node(8L,"部门2-4",3L, 2));
nodes.add(new Node(9L,"部门2-5",4L, 2));
nodes.add(new Node(10L,"部门2-6",4L, 2));
nodes.add(new Node(11L,"部门3-1",5L, 3));
nodes.add(new Node(12L,"部门3-2",5L, 3));
nodes.add(new Node(13L,"部门3-3",6L, 3));
nodes.add(new Node(14L,"部门3-4",6L, 3));
nodes.add(new Node(15L,"部门3-5",7L, 3));
nodes.add(new Node(16L,"部门3-6",7L, 3));
nodes.add(new Node(17L,"部门3-7",8L, 3));
nodes.add(new Node(18L,"部门3-8",8L, 3));
nodes.add(new Node(19L,"部门3-9",9L, 3));
nodes.add(new Node(20L,"部门3-10",9L, 3));
nodes.add(new Node(21L,"部门3-11",10L, 3));
nodes.add(new Node(22L,"部门3-12",10L, 3));
List<Node> list = TreeUtil.build(nodes);
TreeUtil.printTree(list);
}
}
第二版
如果你有一个“公司部门”树,他有一个“医院科室”树,它们都大同小异,那 TreeUtil.java 中将有很多重复的代码。能否将抽象层次提升,搞一个通用的,即带泛型的实现呢?
import lombok.Data;
import java.util.List;
/**
* T可能是公司的部门、医院的科室等实体类
*/
@Data
public class GenericTree<T> {
private T t;
private List<T> children;
}
/**
* 无论是公司的部门,还是医院的科室等实体类,必须有自身ID和父节点ID
*/
public interface IBaseTree {
Long getId();
Long getParentId();
}
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
public class TreeUtil2 {
public static <T extends IBaseTree> List<GenericTree> build(List<T> list){
List<GenericTree> res = new ArrayList<>();
List<T> collect = list.stream().filter(p -> p.getParentId() == 0).collect(Collectors.toList());
for (T t : collect) {
GenericTree ztree = new GenericTree();
setZtree(t, list, ztree);
res.add(ztree);
}
return res;
}
private static <T extends IBaseTree> void setZtree(T t, List<T> list, GenericTree ztree) {
ztree.setT(t);
ztree.setChildren(buildChildren(t, list));
}
private static <T extends IBaseTree> List buildChildren(T t, List<T> list) {
List res = new ArrayList<>();
for (T l : list) {
GenericTree ztree = new GenericTree();
if(Objects.equals(l.getParentId(), t.getId())){
setZtree(l, list, ztree);
res.add(ztree);
}
}
return res;
}
}
import org.apache.commons.collections4.CollectionUtils;
import org.junit.Test;
import java.util.ArrayList;
import java.util.List;
public class Service2Test {
/**
* 只有一级部门
* +----+--------------+----------+-------+
* | id | name | parentId | level |
* +----+--------------+----------+-------+
* | 1 | 某某集团公司 | 0 | 0 |
* | 2 | 部门1-1 | 1 | 1 |
* | 3 | 部门1-2 | 1 | 1 |
* | 4 | 部门1-3 | 1 | 1 |
* +----+--------------+----------+-------+
*/
@Test
public void test() {
// 模拟从数据库中查询出来的结果集
List<Node2> nodes = new ArrayList<>();
nodes.add(new Node2(1L,"某某集团公司",0L, 0));
nodes.add(new Node2(2L,"部门1-1",1L, 1));
nodes.add(new Node2(3L,"部门1-2",1L, 1));
nodes.add(new Node2(4L,"部门1-3",1L, 1));
List<GenericTree> list = TreeUtil2.build(nodes);
printTree(list);
}
/**
* +----+--------------+----------+-------+
* | id | name | parentId | level |
* +----+--------------+----------+-------+
* | 1 | 某某集团公司 | 0 | 0 |
* | 2 | 部门1-1 | 1 | 1 |
* | 3 | 部门1-2 | 1 | 1 |
* | 4 | 部门1-3 | 1 | 1 |
* | 5 | 部门2-1 | 2 | 2 |
* | 6 | 部门2-2 | 2 | 2 |
* | 7 | 部门2-3 | 3 | 2 |
* | 8 | 部门2-4 | 3 | 2 |
* | 9 | 部门2-5 | 4 | 2 |
* | 10 | 部门2-6 | 4 | 2 |
* +----+--------------+----------+-------+
*/
@Test
public void test02() {
// 模拟从数据库中查询出来的结果集
List<Node2> nodes = new ArrayList<>();
nodes.add(new Node2(1L,"某某集团公司",0L, 0));
nodes.add(new Node2(2L,"部门1-1",1L, 1));
nodes.add(new Node2(3L,"部门1-2",1L, 1));
nodes.add(new Node2(4L,"部门1-3",1L, 1));
nodes.add(new Node2(5L,"部门2-1",2L, 2));
nodes.add(new Node2(6L,"部门2-2",2L, 2));
nodes.add(new Node2(7L,"部门2-3",3L, 2));
nodes.add(new Node2(8L,"部门2-4",3L, 2));
nodes.add(new Node2(9L,"部门2-5",4L, 2));
nodes.add(new Node2(10L,"部门2-6",4L, 2));
List<GenericTree> list = TreeUtil2.build(nodes);
printTree(list);
}
/**
* +----+--------------+----------+-------+
* | id | name | parentId | level |
* +----+--------------+----------+-------+
* | 1 | 某某集团公司 | 0 | 0 |
* | 2 | 部门1-1 | 1 | 1 |
* | 3 | 部门1-2 | 1 | 1 |
* | 4 | 部门1-3 | 1 | 1 |
* | 5 | 部门2-1 | 2 | 2 |
* | 6 | 部门2-2 | 2 | 2 |
* | 7 | 部门2-3 | 3 | 2 |
* | 8 | 部门2-4 | 3 | 2 |
* | 9 | 部门2-5 | 4 | 2 |
* | 10 | 部门2-6 | 4 | 2 |
* | 11 | 部门3-1 | 5 | 3 |
* | 12 | 部门3-2 | 5 | 3 |
* | 13 | 部门3-3 | 6 | 3 |
* | 14 | 部门3-4 | 6 | 3 |
* | 15 | 部门3-5 | 7 | 3 |
* | 16 | 部门3-6 | 7 | 3 |
* | 17 | 部门3-7 | 8 | 3 |
* | 18 | 部门3-8 | 8 | 3 |
* | 19 | 部门3-9 | 9 | 3 |
* | 20 | 部门3-10 | 9 | 3 |
* | 21 | 部门3-11 | 10 | 3 |
* | 22 | 部门3-12 | 10 | 3 |
* +----+--------------+----------+-------+
*/
@Test
public void test03() {
// 模拟从数据库中查询出来的结果集
List<Node2> nodes = new ArrayList<>();
nodes.add(new Node2(1L,"某某集团公司",0L, 0));
nodes.add(new Node2(2L,"部门1-1",1L, 1));
nodes.add(new Node2(3L,"部门1-2",1L, 1));
nodes.add(new Node2(4L,"部门1-3",1L, 1));
nodes.add(new Node2(5L,"部门2-1",2L, 2));
nodes.add(new Node2(6L,"部门2-2",2L, 2));
nodes.add(new Node2(7L,"部门2-3",3L, 2));
nodes.add(new Node2(8L,"部门2-4",3L, 2));
nodes.add(new Node2(9L,"部门2-5",4L, 2));
nodes.add(new Node2(10L,"部门2-6",4L, 2));
nodes.add(new Node2(11L,"部门3-1",5L, 3));
nodes.add(new Node2(12L,"部门3-2",5L, 3));
nodes.add(new Node2(13L,"部门3-3",6L, 3));
nodes.add(new Node2(14L,"部门3-4",6L, 3));
nodes.add(new Node2(15L,"部门3-5",7L, 3));
nodes.add(new Node2(16L,"部门3-6",7L, 3));
nodes.add(new Node2(17L,"部门3-7",8L, 3));
nodes.add(new Node2(18L,"部门3-8",8L, 3));
nodes.add(new Node2(19L,"部门3-9",9L, 3));
nodes.add(new Node2(20L,"部门3-10",9L, 3));
nodes.add(new Node2(21L,"部门3-11",10L, 3));
nodes.add(new Node2(22L,"部门3-12",10L, 3));
List<GenericTree> list = TreeUtil2.build(nodes);
printTree(list);
}
private static final class Node2 implements IBaseTree {
private Long id;
private Long parentId;
private String name;
private int level;
public Node2(Long id, String name, Long parentId, int level) {
this.id = id;
this.name = name;
this.parentId = parentId;
this.level = level;
}
@Override
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
@Override
public Long getParentId() {
return parentId;
}
public void setParentId(Long parentId) {
this.parentId = parentId;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getLevel() {
return level;
}
public void setLevel(int level) {
this.level = level;
}
}
/**
* 以可读的样式打印部门树,仅用于调试
* @param list
*/
private static void printTree(List<GenericTree> list) {
if (CollectionUtils.isEmpty(list)) {
return;
}
for (GenericTree ztree : list) {
// TODO 坏的味道
Node2 node = (Node2)ztree.getT();
System.out.println();
int level = node.getLevel();
if (level == 0) {
// 不打印0级
} else if (level == 1) {
System.out.print("" + node.getName());
} else if (level == 2) {
System.out.print(" + " + node.getName());
} else if (level == 3) {
System.out.print(" + " + node.getName());
} else if (level == 4) {
System.out.print(" + " + node.getName());
} else {
throw new IllegalArgumentException("暂时支持到4级");
}
printTree(ztree.getChildren());
}
}
}
把大象装进冰箱里(把树形数据装进数据库表里)
上面说的“树形数据”也可以称之为“层次化数据”(hierarchical data),对于如何装进表里,业界有各种解决思路:
-
Adjacency list (邻接表),就是上面的做法,通俗地讲就是,每个节点只记录自己的父节点,不记录爷爷节点、祖父节点,只需要一张表即可。
-
Closure table (闭合表),通俗地讲就是,每个节点不仅要记录自己的父节点,还要记录自己的爷爷节点、自己的祖父节点、依此类推,需要两张表。这看似复杂,但当需求变态时,还得闭合表好使,例如进行某棵子树的移动。这篇博客有详细讲解,其中某些SQL的写法很有技巧性,从零写还真烧脑。
-
Path enumeration (路径枚举),待补充。
-
Nested Set(嵌套集合),待补充。
资料
- https://blog.csdn.net/weiyifang11/article/details/109516712
- https://www.jianshu.com/p/951b742fd137
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