Java 8 Stream实现菜单树工具类

TreeUtils：

package com.ruoyi.common.core.utils.GuavaUtils.TreeUtils;

import com.alibaba.fastjson.JSON;

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

/**
 * @ProjectName: trunk
 * @Package: com.ruoyi.common.core.utils.GuavaUtils.TreeUtils
 * @ClassName: TreeUtils
 * @Author: lgn
 * @Description:
 * @Date: 2022/4/18 17:45
 * @Version: 1.0
 */
public class TreeUtils {

    /**
     * @Method getMenu
     * @Author lgn
     * @Version  1.0
     * @Description 组装树形菜单
     * @Return
     * @Exception 
     * @Date 2022/4/18 
     */
    private static List<Menu> getMenu(List<Menu> menusList) {
        //组装树形菜单
        List<Menu> collectList = menusList.stream().filter(m -> m.getParentId() == 0).map(
                (m) -> {
                    m.setChildList(getChildrens(m, menusList));
                    return m;
                }
        ).collect(Collectors.toList());//Collector 接口中方法的实现决定了如何对流执行收集操作（如收集到List、Set、Map）。
        return collectList;
    }

    /**
     * 递归查询子节点
     * @param root  根节点
     * @param all   所有节点
     * @return 根节点信息
     */
    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;
    }

    public static void main(String[] args) {

        List<Menu> menusList = 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)
        );

        List<Menu> collectList= getMenu(menusList);

        String jsonOutput= JSON.toJSONString(collectList);
        System.out.println("转json输出结果:"+jsonOutput);
    }

}

Menu VO类

package com.ruoyi.common.core.utils.GuavaUtils.TreeUtils;

import lombok.Builder;
import lombok.Data;

import java.util.List;

/**
 * @ProjectName: trunk
 * @Package: com.ruoyi.common.core.utils.GuavaUtils.TreeUtils
 * @ClassName: Menu
 * @Author: lgn
 * @Description: 菜单类
 * @Date: 2022/4/18 17:43
 * @Version: 1.0
 */
@Data
@Builder
public class Menu {
    /**
     * id
     */
    public Integer id;
    /**
     * 名称
     */
    public String name;
    /**
     * 父id ，根节点为0
     */
    public Integer parentId;
    /**
     * 子节点信息
     */
    public 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;
    }
}