list列表根据父子关系组成树形实例

淡淡的烟草味﹌ 2023-10-05 10:56 69阅读 0赞

最近要开发一个需求，将数据库里面的列表组成一棵树形传给前端。首先我想到的是逐个递归放进去，但是尝试了半天，结果都不对，最终研究出来并不需要递归，一个for循环就搞定了（惭愧，弄了好长时间才弄出来，脑子可能是出去玩儿了）。

实体类：

package com.example.demo;
    
    import lombok.Data;
    
    import java.util.List;
    
    /**
     * @Author: zxy
     * @Description:
     * @Date: 2020/9/29 16:56
     */
    
    @Data
    public class User {
        private int id;
        private int parentId;
        private String name;
        private List<User> children;
    }

初始化及转化为树形：

@Test
    public void test() {
    	List<User> users = new ArrayList<>();
    	User user = new User();
    	user.setId(0);
    	user.setName("zs");
    	users.add(user);
    
    	User user1 = new User();
    	user1.setId(1);
    	user1.setName("zs1");
    	user1.setParentId(0);
    	users.add(user1);
    
    	User user2 = new User();
    	user2.setId(2);
    	user2.setName("zs2");
    	user2.setParentId(1);
    	users.add(user2);
    
    	User user3 = new User();
    	user3.setId(3);
    	user3.setName("zs2");
    	user3.setParentId(1);
    	users.add(user3);
    
    	User user4 = new User();
    	user4.setId(4);
    	user4.setName("zs3");
    	user4.setParentId(2);
    	users.add(user4);
    
    	User user5 = new User();
    	user5.setId(5);
    	user5.setName("zs3");
    	user5.setParentId(2);
    	users.add(user5);
    
    
    	digui2(users);
    	System.out.println("users=====>" + JSON.toJSONString(users));
    }
    
    private void digui2(List<User> users) {
    	for (User user : users) {
    		List<User> childrenUser = new ArrayList<>();
    		for (User user1 : users) {
    			if (Objects.equals(user.getId(), user1.getParentId())) {
    				childrenUser.add(user1);
    			}
    		}
    		user.setChildren(childrenUser);
    	}
    }

说明：

初始化时，list的结构如下：

<table style="width:500px;"> 
 <thead> 
  <tr> 
   <th>ID</th> 
   <th>parentId</th> 
   <th>name</th> 
   <th>children</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>0</td> 
   <td>-</td> 
   <td>zs</td> 
   <td>-</td> 
  </tr> 
  <tr> 
   <td>1</td> 
   <td>0</td> 
   <td>zs1</td> 
   <td>-</td> 
  </tr> 
  <tr> 
   <td>2</td> 
   <td>1</td> 
   <td>zs2</td> 
   <td>-</td> 
  </tr> 
  <tr> 
   <td>3</td> 
   <td>1</td> 
   <td>zs3</td> 
   <td>-</td> 
  </tr> 
  <tr> 
   <td>4</td> 
   <td>2</td> 
   <td>zs4</td> 
   <td>-</td> 
  </tr> 
  <tr> 
   <td>5</td> 
   <td>2</td> 
   <td>zs5</td> 
   <td>-</td> 
  </tr> 
 </tbody> 
</table>

最终组合成的树形结构应该如此（画图软件用的不太熟练，直接上手画了，=\_=）：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0NBVF9jd2Rz_size_16_color_FFFFFF_t_70][]

打印结果：

\[\{"children":\[\{"$ref":".."\},\{"children":\[\{"children":\[\{"children":\[\],"id":4,"name":"zs3","parentId":2\},\{"children":\[\],"id":5,"name":"zs3","parentId":2\}\],"id":2,"name":"zs2","parentId":1\},\{"children":\[\],"id":3,"name":"zs2","parentId":1\}\],"id":1,"name":"zs1","parentId":0\}\],"id":0,"name":"zs","parentId":0\},\{"$ref":"$\[0\].children\[1\]"\},\{"$ref":"$\[0\].children\[1\].children\[0\]"\},\{"$ref":"$\[0\].children\[1\].children\[1\]"\},\{"$ref":"$\[0\].children\[1\].children\[0\].children\[0\]"\},\{"$ref":"$\[0\].children\[1\].children\[0\].children\[1\]"\}\]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0NBVF9jd2Rz_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200930160639542.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L0NBVF9jd2Rz,size_16,color_FFFFFF,t_70