Java 通过map构造树形结构

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<TreeVo> children;


    public static List<TreeVo> allTreeVoList() {

        List<TreeVo> 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<TreeVo> list = TreeVo.allTreeVoList();
        logger.info("结果是:{}", gson.toJson(list));
        Map<Integer, TreeVo> treeVoMap = list.stream().collect(Collectors.toMap(i -> i.getId(), i -> i));
        //获取顶级树节点
        List<TreeVo> 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<TreeVo> 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":[

                        ]
                    }
                ]
            }
        ]
    }
]