java 8 Stream 递归实现树形结构

今天看到一个贴子非常好，利用java 8 的stream实现组织树结构的构建

实体类

/**
 * Menu
 * @author lcry
 */
@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;
    }
}

　测试类

@Test
public void testtree(){
    //模拟从数据库查询出来
    List<Menu> menus = 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)
    );

    //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("-------转json输出结果-------");
    System.out.println(JSON.toJSON(collect));
}
/**
 * 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 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;
}

　　原文地址：https://mp.weixin.qq.com/s?__biz=MzI2NTAzNzgxNw==&mid=2247524590&idx=2&sn=5374a76bc90c976523a474ad4d3f291f&chksm=eaa15278ddd6db6e3638b0f8f563bf93ca28da7e6fd7bc824375d9d5a745c07fcd90b3d43692&scene=21#wechat_redirect