java树结构stream工具类的示例代码详解

package com.example.demo.entity;
 
import lombok.AllArgsConstructor;
import lombok.Builder;
import lombok.Data;
import lombok.NoArgsConstructor;
import java.util.List;
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class Menu {
    
    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;
    }
}

package com.example.demo.util;
 
import cn.hutool.json.JSONUtil;
import com.example.demo.entity.Menu;
import java.util.Arrays;
import java.util.List;
import java.util.Objects;
import java.util.stream.Collectors;
public class TreeUtil {
    
    public 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;
    }
     * @param parentId 父节点id
     * @param menus 菜单集合
     * @return 返回id等于parentId的子孙节点树结构 （不包含id等于parentId的节点）
    public static List<Menu> getTree(Integer parentId, List<Menu> menus) {
        //获取父节点
        List<Menu> tree = menus.stream().filter(m -> Objects.equals(parentId,m.getParentId())).map(
                    m.setChildList(getChildrens(m, menus));
        return tree;
    public static void main(String... args) {
        //模拟从数据库查询出来
        List<Menu> menus = Arrays.asList(
                new Menu(1, "0-1", 0),
                new Menu(2, "0-1-2", 1),
                new Menu(3, "0-1-2-3", 2),
                new Menu(4, "0-1-2-4", 2),
                new Menu(5, "0-1-2-5", 2),
                new Menu(6, "0-6", 0),
                new Menu(7, "0-6-7", 6),
                new Menu(8, "0-6-8", 6),
                new Menu(9, "0-6-7-9", 7),
                new Menu(10, "0-6-7-10", 7),
                new Menu(11, "0-11", 0),
                new Menu(12, "0-11-12", 11)
        );
        List<Menu> tree = getTree(1,menus);
        System.out.println("-------转json输出结果-------");
        System.out.println(JSONUtil.parseArray(tree).toString());
}