java list 转树 tree 的三种写法

jcroad

已于 2023-01-30 15:26:13 修改

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分类专栏： java基础文章标签： java list json

于 2018-03-28 23:09:42 首次发布

本文链接：https://blog.youkuaiyun.com/jcroad/article/details/79735790

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本文介绍了一种将List对象数组转换为树形结构的方法，并提供了三种不同的实现方式。通过使用递归和其他遍历技巧，可以将具有层级关系的数据转换为易于展示的树形结构。

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List对象数组转为tree

代码是自己写的，今天学习来的。下一步，写成工具类。

pom里面加上：阿里的fastjson

<!-- https://mvnrepository.com/artifact/net.sf.json-lib/json-lib -->
<dependency>
  <groupId>net.sf.json-lib</groupId>
  <artifactId>json-lib</artifactId>
  <version>2.4</version>
</dependency>

import com.alibaba.fastjson.JSON;

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

/**
 * <p></p>
 *
 * @package: com.tree
 * @class: TreeNode1
 * @date: 2018/3/27
 * @author: jcroad()
 * @since 1.0
 */
public class TreeNode {

    private Integer id;
    private Integer pid;
    private String name;
    private List<TreeNode> children;

    TreeNode(Integer id, Integer pid, String name) {
        this.id = id;
        this.pid = pid;
        this.name = name;
    }

    public Integer getId() {
        return id;
    }

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

    public Integer getPid() {
        return pid;
    }

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

    public String getName() {
        return name;
    }

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

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

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

    public static void main(String[] args) {
        List<TreeNode> list = new ArrayList<TreeNode>();
        list.add(new TreeNode(1, 0, "1"));
        list.add(new TreeNode(2, 0, "2"));
        list.add(new TreeNode(3, 2, "3"));
        list.add(new TreeNode(4, 3, "4"));
        list.add(new TreeNode(5, 4, "5"));
        list.add(new TreeNode(6, 5, "6"));

        List<TreeNode> treeList = new ArrayList<TreeNode>();
        List<TreeNode> treeList1 = new ArrayList<TreeNode>();
        List<TreeNode> treeList2 = new ArrayList<TreeNode>();
        List<TreeNode> treeList3 = new ArrayList<TreeNode>();
        //方法一、
         treeList = listGetStree(list);
        treeList1 = listToTree(list);
        treeList2 = toTree(list);

        System.out.println(JSON.toJSONString(treeList));
        System.out.println(JSON.toJSONString(treeList1));
        System.out.println(JSON.toJSONString(treeList2));
    }

    private static List<TreeNode> listGetStree(List<TreeNode> list) {
        List<TreeNode> treeList = new ArrayList<TreeNode>();
        for (TreeNode tree : list) {
            //找到根
            if (tree.getPid() == 0) {
                treeList.add(tree);
            }
            //找到子
            for (TreeNode treeNode : list) {
                if (treeNode.getPid() == tree.getId()) {
                    if (tree.getChildren() == null) {
                        tree.setChildren(new ArrayList<TreeNode>());
                    }
                    tree.getChildren().add(treeNode);
                }
            }
        }
        return treeList;
    }

    /**
     * 方法二、
     * @param list
     * @return
     */
    public static List<TreeNode> listToTree(List<TreeNode> list) {
        //用递归找子。
        List<TreeNode> treeList = new ArrayList<TreeNode>();
        for (TreeNode tree : list) {
            if (tree.getPid() == 0) {
                treeList.add(findChildren(tree, list));
            }
        }
        return treeList;
    }

    private static TreeNode findChildren(TreeNode tree, List<TreeNode> list) {
        for (TreeNode node : list) {
            if (node.getPid() == tree.getId()) {
                if (tree.getChildren() == null) {
                    tree.setChildren(new ArrayList<TreeNode>());
                }
                tree.getChildren().add(findChildren(node, list));
            }
        }
        return tree;
    }

    /**
     *方法三
     * @param list
     * @return
     */
    private static List<TreeNode> toTree(List<TreeNode> list) {
        List<TreeNode> treeList = new ArrayList<TreeNode>();
        for (TreeNode tree : list) {
            if(tree.getPid() == 0){
                treeList.add(tree);
            }
        }
        for (TreeNode tree : list) {
            toTreeChildren(treeList,tree);
        }
        return treeList;
    }

    private static void toTreeChildren(List<TreeNode> treeList, TreeNode tree) {
        for (TreeNode node : treeList) {
            if(tree.getPid() == node.getId()){
                if(node.getChildren() == null){
                    node.setChildren(new ArrayList<TreeNode>());
                }
                node.getChildren().add(tree);
            }
            if(node.getChildren() != null){
                toTreeChildren(node.getChildren(),tree);
            }
        }
    }


}