id pid 的數據轉化為樹形結構的數據

“樹”這個結構，在計算機中應該是無處不在的。例如文件目錄樹，數據庫樹索引，組織機構樹等等。對於JavaWeb開發工程師來說，比較常見的有菜單樹，權限樹，組織機構樹等。這些樹形結構的每一個節點通常是存在數據庫表中的，並且每一個節點都是一條獨立的數據。如下，這里規定pid為null的時候，為根節點

 那么如何將這樣的列表數據封裝為樹形結構的數據呢？結構如下

[
    {
        "id": "0",
        "pid": null,
        "name": "全國",
        "children": [
            {
                "id": "1",
                "pid": "0",
                "name": "廣東省",
                "children": [
                    {
                        "id": "4",
                        "pid": "1",
                        "name": "佛山市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "5",
                        "pid": "1",
                        "name": "汕頭市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "6",
                        "pid": "1",
                        "name": "東莞市",
                        "children": [
                            
                        ]
                    }
                ]
            },
            {
                "id": "2",
                "pid": "0",
                "name": "湖北省",
                "children": [
                    {
                        "id": "7",
                        "pid": "2",
                        "name": "黃岡市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "8",
                        "pid": "2",
                        "name": "宜昌市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "9",
                        "pid": "2",
                        "name": "襄陽市",
                        "children": [
                            
                        ]
                    }
                ]
            },
            {
                "id": "3",
                "pid": "0",
                "name": "河南省",
                "children": [
                    {
                        "id": "10",
                        "pid": "3",
                        "name": "洛陽市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "11",
                        "pid": "3",
                        "name": "開封市",
                        "children": [
                            
                        ]
                    },
                    {
                        "id": "12",
                        "pid": "3",
                        "name": "新鄉市",
                        "children": [
                            
                        ]
                    }
                ]
            }
        ]
    }
]

代碼如下

1，節點類

package net.sunmonkey.datatotree;

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

/**
 * 樹結構節點對象類
 * @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，轉換工具類

package net.sunmonkey.datatotree;

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

/**
 * id，pid的列表數據轉化為樹形結構數據
 * @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，測試主方法

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, "全國"));

        list.add(new NodeVo("1", "0", "廣東省"));
        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", "汕頭市"));
        list.add(new NodeVo("6", "1", "東莞市"));
        list.add(new NodeVo("7", "2", "黃岡市"));
        list.add(new NodeVo("8", "2", "宜昌市"));
        list.add(new NodeVo("9", "2", "襄陽市"));
        list.add(new NodeVo("10", "3", "洛陽市"));
        list.add(new NodeVo("11", "3", "開封市"));
        list.add(new NodeVo("12", "3", "新鄉市"));

        System.out.println("轉換前數據：");
        System.out.println(objectMapper.writeValueAsString(list));

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

        System.out.println("轉換后數據：");
        System.out.println(objectMapper.writeValueAsString(result));
    }
}