原文：Java8新特性-使用Stream流递归实现遍历树形结构

import com.alibaba.fastjson.JSONObject;
import lombok.Data;
import org.junit.Test;

import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;

public class Test2Class {

    @Data
    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;
        }

    }



    @Test
    public void test(){
        List<Menu> menus = Arrays.asList(
                new Menu(1,"根节点1",0),
                new Menu(2,"子节点1.1",1),
                new Menu(3,"子节点1.2",1),
                new Menu(4,"子节点1.3",1),
                new Menu(5,"子节点1.4",1),
                new Menu(6,"根节点2",0),
                new Menu(7,"子节点2.1",6),
                new Menu(8,"子节点2.2",6),
                new Menu(9,"子节点2.2.1",8),
                new Menu(10,"子节点2.2.2",8),
                new Menu(11,"根节点3",0),
                new Menu(12,"子节点3.1",11)
        );

        //获取父节点
        List<Menu> collect = menus.stream().filter(m-> m.getParentId()==0).map(
                m->{
                    m.setChildList(getChildrens(m,menus));
                    return m;
                }
        ).collect(Collectors.toList());
        System.out.println(JSONObject.toJSON(collect));
    }



    public List<Menu> getChildrens(Menu root,List<Menu> all){
        List<Menu> children = all.stream().filter(m-> Objects.equals(m.getParentId(),root.getId())).map(
                m->{
                    m.setChildList(getChildrens(m,all));
                    return m;
                }
        ).collect(Collectors.toList());
        return children;
    }

}

getChildrens也可以这么写，写在方法内：

BiFunction<Menu,List<Menu>,List<Menu>> getChildrens =new BiFunction<Menu, List<Menu>, List<Menu>>() {
    @Override
    public List<Menu> apply(Menu root, List<Menu> all) {
        List<Menu> children = all.stream().filter(m-> Objects.equals(m.getParentId(),root.getId())).peek(
            m-> m.setChildList(this.apply(m,all))
        ).collect(Collectors.toList());
        return children;
    }
};