526互联

Java把List集合转成树形结构

发布时间 2023-11-30 11:42:12作者: helloliyh

1. 实体类

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <version>1.18.22</version>
</dependency>
package com.utils;

import lombok.Data;
import java.util.List;

/**
 * @Description:
 * @Author: 
 * @Date: 2021/12/16 9:35
 */
@Data
public class TestEntity {
    private int id;
    private String name;
    private int parentId;
    
    private List<TestEntity> children;

}

2. 方法一：使用Stream流

private static List<TestEntity> listToTree1(List<TestEntity> list) {
    // 要点
    // 通过Collectors.groupingBy(Address::getPid)方法对addresses按照Pid进行分组，也就是将pid相同的放在一起
    Map<Integer, List<TestEntity>> parentMap = list.stream().collect(Collectors.groupingBy(TestEntity::getParentId));
    list.forEach(item -> {
        item.setChildren(parentMap.get(item.getId()));
    });
    // 过滤出根节点集合,根节点已经包含了孩子节点
    List<TestEntity> newList = list.stream().filter(item -> item.getParentId() == 0).collect(Collectors.toList());
    return newList;
}

3. 方法二：使用fastjson

添加依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.73</version>
</dependency>
/**
* @param list          :要转成树的集合
* @param keyMark       :id
* @param parentKeyMark :pid
* @param childMark     :children
* @return List:树集合
* @description :如TestEntity中有字段    int id，String name，int parentId，List<TestEntity> children字段
* keyMark、parentKeyMark、childMark就是    "id", "parentId", "children"
*/
public static List<TestEntity> listToTree2(List<TestEntity> list, String keyMark, String parentKeyMark, String childMark) {
    JSONArray jsonArray = JSONArray.parseArray(JSONObject.toJSONString(list));
    JSONArray jsonArrayTree = new JSONArray();
    JSONObject hash = new JSONObject();
    //将数组转为Object的形式，key为数组中的id
    for (int i = 0; i < jsonArray.size(); i++) {
        JSONObject json = (JSONObject) jsonArray.get(i);
        hash.put(json.getString(keyMark), json);
    }
    //遍历结果集
    for (int j = 0; j < jsonArray.size(); j++) {
        //单条记录
        JSONObject aVal = (JSONObject) jsonArray.get(j);
        //在hash中取出key为单条记录中pid的值
        if (null != aVal.get(parentKeyMark) && !"".equals(aVal.get(parentKeyMark))) {
            JSONObject hashVP = (JSONObject) hash.get(aVal.get(parentKeyMark).toString());
            //如果记录的pid存在，则说明它有父节点，将她添加到孩子节点的集合中
            if (hashVP != null) {
                //检查是否有child属性
                if (hashVP.get(childMark) != null) {
                    JSONArray ch = (JSONArray) hashVP.get(childMark);
                    ch.add(aVal);
                    hashVP.put(childMark, ch);
                } else {
                    JSONArray ch = new JSONArray();
                    ch.add(aVal);
                    hashVP.put(childMark, ch);
                }
            } else {
                jsonArrayTree.add(aVal);
            }
        } else {
            jsonArrayTree.add(aVal);
        }
    }
    return jsonArrayTree.toJavaList(TestEntity.class);
}

4. 方法三：使用递归

/**
* 使用递归方法建树
*
* @param list 要转成树的集合
* @return List
*/
public static List<TestEntity> listToTree2(List<TestEntity> list) {
    List<TestEntity> trees = new ArrayList<>();
    for (TestEntity entity : list) {
        int parentId = entity.getParentId();
        if (parentId == 0) {
            // 是父级
            trees.add(findChildren(entity, list));
        }
    }
    return trees;
}

/**
* 递归查找子节点
*
* @param entity 对象
* @param list 子节点
* @return MenuTree
*/
private static TestEntity findChildren(TestEntity entity, List<TestEntity> list) {
    for (TestEntity info : list) {
        if (entity.getId() == info.getParentId()) {
            if (entity.getChildren() == null) {
                entity.setChildren(new ArrayList<>());
            }
            entity.getChildren().add(findChildren(info, list));
        }
    }
    return entity;
}

5. 完整测试类

package list;

import com.alibaba.fastjson.JSONArray;
import com.alibaba.fastjson.JSONObject;

import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class ListToTreeTest {
    public static void main(String[] args) {
        List<TestEntity> list = new ArrayList<>();

        TestEntity testEntity1 = new TestEntity();
        testEntity1.setId(1);
        testEntity1.setName("张三");
        testEntity1.setParentId(0);

        TestEntity testEntity2 = new TestEntity();
        testEntity2.setId(2);
        testEntity2.setName("李四");
        testEntity2.setParentId(0);

        TestEntity testEntity3 = new TestEntity();
        testEntity3.setId(3);
        testEntity3.setName("张三儿子");
        testEntity3.setParentId(1);

        list.add(testEntity1);
        list.add(testEntity2);
        list.add(testEntity3);


        List<TestEntity> result1 = listToTree1(list);
        System.out.println(result1);

//        List<TestEntity> result2 = listToTree2(list, "id", "parentId", "children");
//        System.out.println(result2);

//        List<TestEntity> result3 = listToTree3(list);
//        System.out.println(result3);

    }

    private static List<TestEntity> listToTree1(List<TestEntity> list) {
        // 要点
        // 通过Collectors.groupingBy(Address::getPid)方法对addresses按照Pid进行分组，也就是将pid相同的放在一起
        Map<Integer, List<TestEntity>> parentMap = list.stream().collect(Collectors.groupingBy(TestEntity::getParentId));
        list.forEach(item -> {
            item.setChildren(parentMap.get(item.getId()));
        });
        // 过滤出根节点集合,根节点已经包含了孩子节点
        List<TestEntity> newList = list.stream().filter(item -> item.getParentId() == 0).collect(Collectors.toList());
        return newList;
    }

    /**
     * @param list          :要转成树的集合
     * @param keyMark       :id
     * @param parentKeyMark :pid
     * @param childMark     :children
     * @return List:树集合
     * @description :如TestEntity中有字段    int id，String name，int parentId，List<TestEntity> children字段
     * keyMark、parentKeyMark、childMark就是    "id", "parentId", "children"
     */
    public static List<TestEntity> listToTree2(List<TestEntity> list, String keyMark, String parentKeyMark, String childMark) {
        JSONArray jsonArray = JSONArray.parseArray(JSONObject.toJSONString(list));
        JSONArray jsonArrayTree = new JSONArray();
        JSONObject hash = new JSONObject();
        //将数组转为Object的形式，key为数组中的id
        for (int i = 0; i < jsonArray.size(); i++) {
            JSONObject json = (JSONObject) jsonArray.get(i);
            hash.put(json.getString(keyMark), json);
        }
        //遍历结果集
        for (int j = 0; j < jsonArray.size(); j++) {
            //单条记录
            JSONObject aVal = (JSONObject) jsonArray.get(j);
            //在hash中取出key为单条记录中pid的值
            if (null != aVal.get(parentKeyMark) && !"".equals(aVal.get(parentKeyMark))) {
                JSONObject hashVP = (JSONObject) hash.get(aVal.get(parentKeyMark).toString());
                //如果记录的pid存在，则说明它有父节点，将她添加到孩子节点的集合中
                if (hashVP != null) {
                    //检查是否有child属性
                    if (hashVP.get(childMark) != null) {
                        JSONArray ch = (JSONArray) hashVP.get(childMark);
                        ch.add(aVal);
                        hashVP.put(childMark, ch);
                    } else {
                        JSONArray ch = new JSONArray();
                        ch.add(aVal);
                        hashVP.put(childMark, ch);
                    }
                } else {
                    jsonArrayTree.add(aVal);
                }
            } else {
                jsonArrayTree.add(aVal);
            }
        }
        return jsonArrayTree.toJavaList(TestEntity.class);
    }

    /**
     * 使用递归方法建树
     *
     * @param list 要转成树的集合
     * @return List
     */
    public static List<TestEntity> listToTree3(List<TestEntity> list) {
        List<TestEntity> trees = new ArrayList<>();
        for (TestEntity entity : list) {
            int parentId = entity.getParentId();
            if (parentId == 0) {
                // 是父级
                trees.add(findChildren(entity, list));
            }
        }
        return trees;
    }

    /**
     * 递归查找子节点
     *
     * @param entity 对象
     * @param list   子节点
     * @return MenuTree
     */
    private static TestEntity findChildren(TestEntity entity, List<TestEntity> list) {
        for (TestEntity info : list) {
            if (entity.getId() == info.getParentId()) {
                if (entity.getChildren() == null) {
                    entity.setChildren(new ArrayList<>());
                }
                entity.getChildren().add(findChildren(info, list));
            }
        }
        return entity;
    }
}