Java编程：将具有父子关系的数据库表数据转换为树形结构，支持无限层级

在平时的开发工作中，经常遇到这样一个场景，在数据库中存储了具有父子关系的数据，需要将这些数据以树形结构的形式在界面上进行展示。本文的目的是提供了一个通用的编程模型，解决将具有父子关系的数据转换成树形结构的问题。如有不正之处，欢迎大家批评指正。

编程模型

我们以北京行政区划为例，讲解整个模型。

北京市：市辖区县

市辖区：东城区西城区朝阳区丰台区石景山区海淀区门头沟区房山区通州区顺义区昌平区大兴区怀柔区平谷区

县：密云县延庆县

UML类图如下：

TreeNode:定义树的节点对象

nodeId：树节点Id。
nodeName：树节点名称。
parentNodeId：树节点父Id。
orderNum：节点在树中的排序号，在同一节点下进行排序。
level：当前树节点所在的层级，根节点为第一层。
parent：当前树节点的父节点。
children：当前树节点的儿子节点。
allChildren：当前树节点的子孙节点。

ITree：定义树对象要实现的方法。

getTree()：以 List 形式返回树的所有的 TreeNode 对象。
getRoot()：以 List 形式返回树的根节点，可能是一个或者多个。
getTreeNode(String nodeId)：根据 nodeId 返回对应的 TreeNode 对象。

Tree：实现 ITree 接口，提供树的完整功能。

getTree()：以 List 形式返回树的所有的 TreeNode 对象。
getRoot()：以 List 形式返回树的根节点，可能是一个或者多个。
getTreeNode(String nodeId)：根据 nodeId 返回对应的 TreeNode 对象。

ITreeNode：定义模板方法，构造树形结构的类要实现该接口，Tree 通过调用该接口中的方法获取 nodeId nodeName parentNodeId orderNum 数据。

getNodeId()：获取树节点Id。
getNodeName()：获取树节点名称。
getParentNodeId()：获取树节点父Id。
getOrderNum()：获取节点在树中的排序号，在同一节点下进行排序。

Org：定义行政区划类，实现 ItreeNode 接口。

实现代码

TreeNode类：

package com.ips.tree;import java.util.ArrayList;
import java.util.List;import com.alibaba.fastjson.annotation.JSONField;/*** <p>Title: 树节点</p>* <p>Description:一棵树由许多包含父子关系的节点组成 </p>* @author  liuzhibo* @date    2017年1月18日*/
public class TreeNode {//树节点ID@JSONField(ordinal=1)private String nodeId;//树节点名称@JSONField(ordinal=2)private String nodeName;//父节点ID@JSONField(ordinal=3)private String parentNodeId;//节点在树中的排序号@JSONField(ordinal=4)private int orderNum;//节点所在的层级@JSONField(ordinal=5)private int level;private TreeNode parent;//当前节点的二子节点@JSONField(ordinal=6)private List<TreeNode> children = new ArrayList<TreeNode>();//当前节点的子孙节点private List<TreeNode> allChildren = new ArrayList<TreeNode>();public TreeNode(ITreeNode obj){this.nodeId = obj.getNodeId();this.nodeName = obj.getNodeName();this.parentNodeId = obj.getNodeParentId();this.orderNum = obj.getOrderNum();}public void addChild(TreeNode treeNode){this.children.add(treeNode);}public void removeChild(TreeNode treeNode){this.children.remove(treeNode);}public String getNodeId() {return nodeId;}public void setNodeId(String nodeId) {this.nodeId = nodeId;}public String getNodeName() {return nodeName;}public void setNodeName(String nodeName) {this.nodeName = nodeName;}public String getParentNodeId() {return parentNodeId;}public void setParentNodeId(String parentNodeId) {this.parentNodeId = parentNodeId;}public int getLevel() {return level;}public void setLevel(int level) {this.level = level;}public TreeNode getParent() {return parent;}public void setParent(TreeNode parent) {this.parent = parent;}public List<TreeNode> getChildren() {return children;}public void setChildren(List<TreeNode> children) {this.children = children;}public int getOrderNum() {return orderNum;}public void setOrderNum(int orderNum) {this.orderNum = orderNum;}public List<TreeNode> getAllChildren() {if(this.allChildren.isEmpty()){for(TreeNode treeNode : this.children){this.allChildren.add(treeNode);this.allChildren.addAll(treeNode.getAllChildren());}}return this.allChildren;}
}

ITree接口：

package com.ips.tree;import java.util.List;public interface ITree {public List<TreeNode> getTree();public List<TreeNode> getRoot();public TreeNode getTreeNode(String nodeId);
}

Tree类：

package com.ips.tree;import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;public class Tree implements ITree {private HashMap<String, TreeNode> treeNodesMap = new HashMap<String, TreeNode>();private List<TreeNode> treeNodesList = new ArrayList<TreeNode>();public Tree(List<ITreeNode> list){initTreeNodeMap(list);initTreeNodeList();}private void initTreeNodeMap(List<ITreeNode> list){TreeNode treeNode = null;for(ITreeNode item : list){treeNode = new TreeNode(item);treeNodesMap.put(treeNode.getNodeId(), treeNode);}Iterator<TreeNode> iter = treeNodesMap.values().iterator();TreeNode parentTreeNode = null;while(iter.hasNext()){treeNode = iter.next();if(treeNode.getParentNodeId() == null || treeNode.getParentNodeId() == ""){continue;}parentTreeNode = treeNodesMap.get(treeNode.getParentNodeId());if(parentTreeNode != null){treeNode.setParent(parentTreeNode);parentTreeNode.addChild(treeNode);}}}private void initTreeNodeList(){if(treeNodesList.size() > 0){return;}if(treeNodesMap.size() == 0){return;}Iterator<TreeNode> iter = treeNodesMap.values().iterator();TreeNode treeNode = null;while(iter.hasNext()){treeNode = iter.next();if(treeNode.getParent() == null){this.treeNodesList.add(treeNode);this.treeNodesList.addAll(treeNode.getAllChildren());}}}@Overridepublic List<TreeNode> getTree() {return this.treeNodesList;}@Overridepublic List<TreeNode> getRoot() {List<TreeNode> rootList = new ArrayList<TreeNode>();if (this.treeNodesList.size() > 0) {for (TreeNode node : treeNodesList) {if (node.getParent() == null)rootList.add(node);}}return rootList;}@Overridepublic TreeNode getTreeNode(String nodeId) {return this.treeNodesMap.get(nodeId);}}

ITreeNode 接口：

package com.ips.tree;public interface ITreeNode {public String getNodeId();public String getNodeName();public String getNodeParentId();public Integer getOrderNum();
}

Org 类：

package com.ips.tree;public class Org implements ITreeNode {private String uuid;private String parentId;private String name;private Integer orderNum;private String code;private String type;public Org(){}public Org(String uuid, String parentId, String name, Integer orderNum, String code, String type){this.uuid = uuid;this.parentId = parentId;this.name = name;this.orderNum = orderNum;this.code = code;this.type = type;}@Overridepublic String getNodeId() {return this.uuid;}@Overridepublic String getNodeName() {return this.name;}@Overridepublic String getNodeParentId() {return this.parentId;}@Overridepublic Integer getOrderNum() {return this.orderNum;}public String getUuid() {return uuid;}public void setUuid(String uuid) {this.uuid = uuid;}public String getParentId() {return parentId;}public void setParentId(String parentId) {this.parentId = parentId;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getCode() {return code;}public void setCode(String code) {this.code = code;}public String getType() {return type;}public void setType(String type) {this.type = type;}public void setOrderNum(Integer orderNum) {this.orderNum = orderNum;}}

TreeDemo 类：执行该类的 main 方法，查看效果。

package com.ips.tree;import java.util.ArrayList;
import java.util.List;import com.alibaba.fastjson.JSONObject;
import com.alibaba.fastjson.serializer.SimplePropertyPreFilter;public class TreeDemo {public static void main(String[] args) {Tree tree = new Tree(genOrgList());TreeNode treeNode = tree.getTreeNode("2");SimplePropertyPreFilter filter = new SimplePropertyPreFilter(); // 构造方法里，也可以直接传需要序列化的属性名字filter.getExcludes().add("parent");filter.getExcludes().add("allChildren");String data = JSONObject.toJSONString(treeNode, filter);System.out.println(data);}public static List<ITreeNode> genOrgList(){List<ITreeNode> list = new ArrayList<ITreeNode>();Org org = new Org("2", "1", "北京市", 2, "110000", "2");list.add(org);org = new Org("3", "2", "市辖区", 3, "110100", "3");list.add(org);org = new Org("4", "3", "东城区", 4, "110101", "4");list.add(org);org = new Org("5", "3", "东城区", 5, "110102", "4");list.add(org);org = new Org("6", "3", "东城区", 6, "110105", "4");list.add(org);org = new Org("7", "3", "东城区", 7, "110106", "4");list.add(org);org = new Org("8", "3", "东城区", 8, "110107", "4");list.add(org);org = new Org("9", "3", "东城区", 9, "110108", "4");list.add(org);org = new Org("10", "3", "东城区", 10, "110109", "4");list.add(org);org = new Org("11", "3", "东城区", 11, "110111", "4");list.add(org);org = new Org("12", "3", "东城区", 12, "110112", "4");list.add(org);org = new Org("13", "3", "东城区", 13, "110113", "4");list.add(org);org = new Org("14", "3", "东城区", 14, "110114", "4");list.add(org);org = new Org("15", "3", "东城区", 15, "110115", "4");list.add(org);org = new Org("16", "3", "东城区", 16, "110116", "4");list.add(org);org = new Org("17", "3", "东城区", 17, "110117", "4");list.add(org);org = new Org("18", "2", "县", 3, "110200", "3");list.add(org);org = new Org("19", "18", "密云县", 19, "110228", "4");list.add(org);org = new Org("20", "18", "延庆县", 20, "110229", "4");list.add(org);return list;}}

执行结果如下：

{"nodeId": "2","nodeName": "北京市","parentNodeId": "1","orderNum": 2,"level": 0,"children": [{"nodeId": "18","nodeName": "县","parentNodeId": "2","orderNum": 3,"level": 0,"children": [{"nodeId": "19","nodeName": "密云县","parentNodeId": "18","orderNum": 19,"level": 0,"children": []},{"nodeId": "20","nodeName": "延庆县","parentNodeId": "18","orderNum": 20,"level": 0,"children": []}]},{"nodeId": "3","nodeName": "市辖区","parentNodeId": "2","orderNum": 3,"level": 0,"children": [{"nodeId": "17","nodeName": "东城区","parentNodeId": "3","orderNum": 17,"level": 0,"children": []},{"nodeId": "15","nodeName": "东城区","parentNodeId": "3","orderNum": 15,"level": 0,"children": []},{"nodeId": "16","nodeName": "东城区","parentNodeId": "3","orderNum": 16,"level": 0,"children": []},{"nodeId": "13","nodeName": "东城区","parentNodeId": "3","orderNum": 13,"level": 0,"children": []},{"nodeId": "14","nodeName": "东城区","parentNodeId": "3","orderNum": 14,"level": 0,"children": []},{"nodeId": "11","nodeName": "东城区","parentNodeId": "3","orderNum": 11,"level": 0,"children": []},{"nodeId": "12","nodeName": "东城区","parentNodeId": "3","orderNum": 12,"level": 0,"children": []},{"nodeId": "10","nodeName": "东城区","parentNodeId": "3","orderNum": 10,"level": 0,"children": []},{"nodeId": "7","nodeName": "东城区","parentNodeId": "3","orderNum": 7,"level": 0,"children": []},{"nodeId": "6","nodeName": "东城区","parentNodeId": "3","orderNum": 6,"level": 0,"children": []},{"nodeId": "5","nodeName": "东城区","parentNodeId": "3","orderNum": 5,"level": 0,"children": []},{"nodeId": "4","nodeName": "东城区","parentNodeId": "3","orderNum": 4,"level": 0,"children": []},{"nodeId": "9","nodeName": "东城区","parentNodeId": "3","orderNum": 9,"level": 0,"children": []},{"nodeId": "8","nodeName": "东城区","parentNodeId": "3","orderNum": 8,"level": 0,"children": []}]}]
}

注：该示例中使用了 alibaba 的 fastjson 实现类对象序列化，maven 依赖如下：

<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.20</version>
</dependency>