id pid 的数据转化为树形结构的数据

“树”这个结构，在计算机中应该是无处不在的。例如文件目录树，数据库树索引，组织机构树等等。对于JavaWeb开发工程师来说，比较常见的有菜单树，权限树，组织机构树等。这些树形结构的每一个节点通常是存在数据库表中的，并且每一个节点都是一条独立的数据。如下，这里规定pid为null的时候，为根节点

 那么如何将这样的列表数据封装为树形结构的数据呢？结构如下

[
    {
        "id": "0",
        "pid": null,
        "name": "全国",
        "children": [
            {
                "id": "1",
                "pid": "0",
                "name": "广东省",
                "children": [
                    {
                        "id": "4",
                        "pid": "1",
                        "name": "佛山市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "5",
                        "pid": "1",
                        "name": "汕头市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "6",
                        "pid": "1",
                        "name": "东莞市",
                        "children": [
                            
                        ]
                    }
                ]
            },
            {
                "id": "2",
                "pid": "0",
                "name": "湖北省",
                "children": [
                    {
                        "id": "7",
                        "pid": "2",
                        "name": "黄冈市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "8",
                        "pid": "2",
                        "name": "宜昌市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "9",
                        "pid": "2",
                        "name": "襄阳市",
                        "children": [
                            
                        ]
                    }
                ]
            },
            {
                "id": "3",
                "pid": "0",
                "name": "河南省",
                "children": [
                    {
                        "id": "10",
                        "pid": "3",
                        "name": "洛阳市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "11",
                        "pid": "3",
                        "name": "开封市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "12",
                        "pid": "3",
                        "name": "新乡市",
                        "children": [
                            
                        ]
                    }
                ]
            }
        ]
    }
]

代码如下

1，节点类

package net.sunmonkey.datatotree;

import java.util.LinkedList;
import java.util.List;

/**
 * 树结构节点对象类
 * @author Wenqin Cheng
 */
public class NodeVo {

    private String id;

    private String pid;

    private String name;

    private List<NodeVo> children;

    public NodeVo() {
        children = new LinkedList<>();
    }

    public NodeVo(String id, String pid, String name) {
        this.id = id;
        this.pid = pid;
        this.name = name;
        this.children = new LinkedList<>();
    }

    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getPid() {
        return pid;
    }

    public void setPid(String pid) {
        this.pid = pid;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public List<NodeVo> getChildren() {
        return children;
    }

    public void setChildren(List<NodeVo> children) {
        this.children = children;
    }

    @Override
    public String toString() {
        return "NodeVo{" +
                "id='" + id + '\'' +
                ", pid='" + pid + '\'' +
                ", name='" + name + '\'' +
                ", children=" + children +
                '}';
    }
}

 

2，转换工具类

package net.sunmonkey.datatotree;

import java.util.LinkedList;
import java.util.List;

/**
 * id，pid的列表数据转化为树形结构数据
 * @author Wenqin Cheng
 */
public class ConvertUtil {
    
    public static List<NodeVo> getTreeData(List<NodeVo> list) {

        List<NodeVo> tree = new LinkedList<>();
        if(null != list && !list.isEmpty()){
            for(NodeVo nodeVo: list){
                addToTreeNodeList(list, nodeVo);
            }

            for (NodeVo nodeVo: list){
                if(null == nodeVo.getPid()){
                    tree.add(nodeVo);
                }
            }
        }

        return tree;
    }

    private static void addToTreeNodeList(final List<NodeVo> nodeVoList, NodeVo treeNodeVo){
        if(null != nodeVoList && !nodeVoList.isEmpty()){
            for(NodeVo parentNodeVo: nodeVoList){
                if(parentNodeVo.getId().equals(treeNodeVo.getPid())){
                    List<NodeVo> children = parentNodeVo.getChildren();
                    boolean flag = true;
                    for(NodeVo node: children){
                        if(treeNodeVo.getId().equals(node.getId())){
                            flag = false;
                        }
                    }
                    if(flag){
                        children.add(treeNodeVo);
                    }
                    break;
                }else{
                    addToTreeNodeList(parentNodeVo.getChildren(), treeNodeVo);
                }
            }
        }
    }
}

 

3，测试主方法

package net.sunmonkey.datatotree;

import com.fasterxml.jackson.databind.ObjectMapper;

import java.util.LinkedList;
import java.util.List;

/**
 * 主方法
 * @author Wenqin Cheng
 */
public class MainClass {

    static ObjectMapper objectMapper = new ObjectMapper();

    public static void main(String[] args) throws Exception {

        List<NodeVo> list = new LinkedList<>();

        list.add(new NodeVo("0", null, "全国"));

        list.add(new NodeVo("1", "0", "广东省"));
        list.add(new NodeVo("2", "0", "湖北省"));
        list.add(new NodeVo("3", "0", "河南省"));

        list.add(new NodeVo("4", "1", "佛山市"));
        list.add(new NodeVo("5", "1", "汕头市"));
        list.add(new NodeVo("6", "1", "东莞市"));
        list.add(new NodeVo("7", "2", "黄冈市"));
        list.add(new NodeVo("8", "2", "宜昌市"));
        list.add(new NodeVo("9", "2", "襄阳市"));
        list.add(new NodeVo("10", "3", "洛阳市"));
        list.add(new NodeVo("11", "3", "开封市"));
        list.add(new NodeVo("12", "3", "新乡市"));

        System.out.println("转换前数据：");
        System.out.println(objectMapper.writeValueAsString(list));

        List<NodeVo> result = ConvertUtil.getTreeData(list);

        System.out.println("转换后数据：");
        System.out.println(objectMapper.writeValueAsString(result));
    }
}