【utils】用于前端展示树结构的工具类

应用场景 : 有的时候 , 前端需要展示出一个分类以及这个分类下的子分类 , 一层一层形成树结构

定义节点

首先定义每一个类型为一个节点 , 定义它的必要属性

package com.starw.cloudy.utils.treeTools;

import java.util.ArrayList;
import java.util.List;

/**
 * 节点
 */
public class Node {
    //节点的唯一id,此处可以对应数据库中的主键,根据实际情况可以修改
    private int id;
    //节点需要展示的名称
    private String name;
    //顶级节点没有父id, 因此允许null的存在, 要用Integer
    private Integer parentId;
    //是否展开树内容
    private int expand;
    //节点的子节点集合
    private List<Node> children;

    public Node(int id, String name, Integer parentId, int expand) {
        this.id = id;
        this.name = name;
        this.parentId = parentId;
        this.expand = expand;
        this.children = new ArrayList<>();
    }

    public Node(int id, String name, Integer parentId, int expand, List<Node> children) {
        this.id = id;
        this.name = name;
        this.parentId = parentId;
        this.expand = expand;
        this.children = children;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public Integer getParentId() {
        return parentId;
    }

    public void setParentId(Integer parentId) {
        this.parentId = parentId;
    }

    public int getExpand() {
        return expand;
    }

    public void setExpand(int expand) {
        this.expand = expand;
    }

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

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

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

建树工具

package com.starw.cloudy.utils.treeTools;

import com.alibaba.fastjson.JSONArray;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 * Created by dell on 2017/12/22.
 */
public class TreeUtil {

    public static JSONArray buildTree(List<Node> nodes) {
        JSONArray result = new JSONArray();
        Iterator<Node> iterator = nodes.iterator();
        while (iterator.hasNext()) {
            Node node = iterator.next();
            if (node.getParentId() == null) {//没有父id, 为顶级父类,要从顶级父类开始
                //将此node和所有的node传入
                buildNode(node, nodes);
                //递归完毕,此处是一个顶级节点下的所有子节点,装入结果集
                result.add(node);
            }
        }
        return result;
    }

    private static Node buildNode(Node parent, List<Node> nodes) {
        Iterator<Node> iterator = nodes.iterator();
        while (iterator.hasNext()) {
            Node node = iterator.next();
            if (node.getParentId() != null && node.getParentId().intValue() == parent.getId()) {
                parent.getChildren().add(node);
                //此处递归,一直查找此子节点
                buildNode(node, nodes);
            }
        }
        return parent;
    }

    public static void main(String[] args) {
        //测试
        List<Node> nodes = new ArrayList<>();
        //id name parentId expend children
        Node a = new Node(1, "A", null, 0, new ArrayList<>());
        Node b = new Node(2, "B", 1, 0, new ArrayList<>());
        Node c = new Node(3, "C", 1, 0, new ArrayList<>());
        Node d = new Node(4, "D", 3, 0, new ArrayList<>());
        Node e = new Node(5, "E", 3, 0, new ArrayList<>());
        Node f = new Node(6, "F", 5, 0, new ArrayList<>());
        Node g = new Node(7, "G", null, 0, new ArrayList<>());
        nodes.add(a);
        nodes.add(b);
        nodes.add(c);
        nodes.add(d);
        nodes.add(e);
        nodes.add(f);
        nodes.add(g);

        System.out.println(buildTree(nodes));
    }
}

测试结果

[{"children":[{"children":[],"expand":0,"id":2,"name":"B","parentId":1},{"children":[{"children":[],"expand":0,"id":4,"name":"D","parentId":3},{"children":[{"children":[],"expand":0,"id":6,"name":"F","parentId":5}],"expand":0,"id":5,"name":"E","parentId":3}],"expand":0,"id":3,"name":"C","parentId":1}],"expand":0,"id":1,"name":"A"},{"children":[],"expand":0,"id":7,"name":"G"}]