在开发中，经常会有将 数据组装成为树形结构的场景，除了可以通过递归实现，还可以通过map 组装实现。

一，构造基本数据

import apple.laf.JRSUIUtils;

import com.google.common.collect.Lists;

import lombok.AllArgsConstructor;

import lombok.Builder;

import lombok.Data;

import lombok.NoArgsConstructor;

import java.util.ArrayList;

import java.util.List;

/**

* @创建人

* @创建时间 2020/5/25

* @描述

*/

@Data

@Builder

@AllArgsConstructor

@NoArgsConstructor

public class TreeVo {

private int id;

private String name;

private int parent;

private List children;

public static List allTreeVoList() {

List list = Lists.newArrayList();

TreeVo heBeiTreeVo = TreeVo.builder().id(1).name("河北").parent(0).children(Lists.newArrayList()).build();

list.add(heBeiTreeVo);

TreeVo hanTreeVo = TreeVo.builder().id(2).name("邯郸").parent(1).children(Lists.newArrayList()).build();

list.add(hanTreeVo);

TreeVo weiTreeVo = TreeVo.builder().id(3).name("魏县").parent(2).children(Lists.newArrayList()).build();

list.add(weiTreeVo);

TreeVo beiTreeVo = TreeVo.builder().id(4).name("北京").parent(0).children(Lists.newArrayList()).build();

list.add(beiTreeVo);

TreeVo jingTreeVo = TreeVo.builder().id(5).name("北京市").parent(4).children(Lists.newArrayList()).build();

list.add(jingTreeVo);

TreeVo chaoTreeVo = TreeVo.builder().id(6).name("朝阳区").parent(5).children(Lists.newArrayList()).build();

list.add(chaoTreeVo);

return list;

}

}

二，通过map分组遍历

/**

* 组装树

*/

public void wrapperTreeTest() {

Gson gson = new Gson();

List list = TreeVo.allTreeVoList();

logger.info("结果是:{}", gson.toJson(list));

Map treeVoMap = list.stream().collect(Collectors.toMap(i -> i.getId(), i -> i));

//获取顶级树节点

List rootList = list.stream().filter(i -> !treeVoMap.containsKey(i.getParent())).collect(toList());

logger.info("rootList is:{}", gson.toJson(rootList));

for (TreeVo treeVo : list) {

if (treeVoMap.containsKey(treeVo.getParent())) {

TreeVo parentTree = treeVoMap.get(treeVo.getParent());

List children = parentTree.getChildren();

children.add(treeVo);

}

}

logger.info("最后树结构是:{}", gson.toJson(rootList));

}

三，结果是

[

{

"id":1,

"name":"河北",

"parent":0,

"children":[

{

"id":2,

"name":"邯郸",

"parent":1,

"children":[

{

"id":3,

"name":"魏县",

"parent":2,

"children":[

]

}

]

}

]

},

{

"id":4,

"name":"北京",

"parent":0,

"children":[

{

"id":5,

"name":"北京市",

"parent":4,

"children":[

{

"id":6,

"name":"朝阳区",

"parent":5,

"children":[

]

}

]

}

]

}

]