Java 8 中的 Stream 轻松遍历树形结构
2023-12-28 16:51:50
在平时的需求开发中,我们经常会遍历一些树形结构,数据库中使用父id来关联,为了降低数据库的查询压力,我们可以使用java8中的Stream流一次性把数据查出来,然后通过流式处理。
实体类:Menu.java
package com.example.tree;
import java.util.List;
/**
* 菜单实体类
* @date: 2023/12/28
**/
public class Menu {
private Integer id;
private String name;
private Integer parentId;
private List<Menu> childList;
public Menu(Integer id, String name, Integer parentId) {
this.id = id;
this.name = name;
this.parentId = parentId;
}
public Menu(Integer id, String name, Integer parentId, List<Menu> childList) {
this.id = id;
this.name = name;
this.parentId = parentId;
this.childList = childList;
}
public Integer getId() {
return id;
}
public void setId(Integer 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 List<Menu> getChildList() {
return childList;
}
public void setChildList(List<Menu> childList) {
this.childList = childList;
}
}
模拟查看数据库所有数据到List里面
测试类:testTree.java
package com.example.tree;
import com.alibaba.fastjson.JSON;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
/**
* 测试树
* @date: 2023/12/28
**/
public class testTree {
public static void main(String[] args) {
List<Menu> menuList = Arrays.asList(
new Menu(1,"根节点",0),
new Menu(2,"子节点1",1),
new Menu(3,"子节点1.1",2),
new Menu(4,"子节点1.2",2),
new Menu(5,"根节点1.3",2),
new Menu(6,"根节点2",1),
new Menu(7,"根节点2.1",6),
new Menu(8,"根节点2.2",6),
new Menu(9,"根节点2.2.1",7),
new Menu(10,"根节点2.2.2",7),
new Menu(11,"根节点3",1),
new Menu(12,"根节点3.1",11)
);
//获取父节点
List<Menu> collect = menuList.stream().filter(m -> m.getParentId() == 0).map((m) -> {
m.setChildList(getChildrens(m,menuList));
return m;
}).collect(Collectors.toList());
System.out.println("============转json输出结果:");
System.out.println(JSON.toJSON(collect));
}
/**
* 递归查询子节点
* @param root 根节点
* @param all 所有节点
* @return 根节点信息
* @date 2023/12/28
*/
private static List<Menu> getChildrens(Menu root, List<Menu> all) {
List<Menu> children = all.stream().filter(m -> {
return Objects.equals(m.getParentId(),root.getId());
}).map(
(m) -> {
m.setChildList(getChildrens(m,all));
return m;
}
).collect(Collectors.toList());
return children;
}
}
打印结果:
[
{
"name":"根节点",
"childList":[
{
"name":"子节点1",
"childList":[
{
"name":"子节点1.1",
"childList":[
],
"id":3,
"parentId":2
},
{
"name":"子节点1.2",
"childList":[
],
"id":4,
"parentId":2
},
{
"name":"根节点1.3",
"childList":[
],
"id":5,
"parentId":2
}
],
"id":2,
"parentId":1
},
{
"name":"根节点2",
"childList":[
{
"name":"根节点2.1",
"childList":[
{
"name":"根节点2.2.1",
"childList":[
],
"id":9,
"parentId":7
},
{
"name":"根节点2.2.2",
"childList":[
],
"id":10,
"parentId":7
}
],
"id":7,
"parentId":6
},
{
"name":"根节点2.2",
"childList":[
],
"id":8,
"parentId":6
}
],
"id":6,
"parentId":1
},
{
"name":"根节点3",
"childList":[
{
"name":"根节点3.1",
"childList":[
],
"id":12,
"parentId":11
}
],
"id":11,
"parentId":1
}
],
"id":1,
"parentId":0
}
]
文章来源:https://blog.csdn.net/wlchina123/article/details/135270813
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