Java jdk8實現 部門樹的遞迴編寫

package com.otc.infra.utils;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Department {

    private Integer id;

    private String name;

    private Integer parentId;

    private List<Department> children = new ArrayList<>();

    public Department(Integer id, String name, Integer parentId) {
        this.id = id;
        this.name = name;
        this.parentId = parentId;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Integer getParentId() {
        return parentId;
    }

    public void setParentId(Integer parentId) {
        this.parentId = parentId;
    }

    public List<Department> getChildren() {
        return children;
    }

    public void setChildren(List<Department> children) {
        this.children = children;
    }


    public static void main(String[] args) {
        List<Department> departmentList = new ArrayList<>();
        departmentList.add(new Department(1, "白鬍子", null));
        departmentList.add(new Department(2, "不死鳥", 1));
        departmentList.add(new Department(3, "艾斯", 1));
        departmentList.add(new Department(4, "龍", null));
        departmentList.add(new Department(5, "路飛", 4));
        departmentList.add(new Department(6, "索隆", 5));
        departmentList.add(new Department(7, "娜美", 5));
        departmentList.add(new Department(8, "羅賓", 5));
        departmentList.add(new Department(9, "烏索普", 5));
        departmentList.add(new Department(10, "小丑", 100));//小丑的長官Id不存在，所以tree中沒有它的資訊
        List<Department> tree = makeTree(departmentList, null);
        System.out.println("-------------------------->");
    }

   private static List<Department> makeTree(List<Department> departmentList, Integer pId) {
        //子類
        List<Department> children = departmentList.stream().filter(x -> x.getParentId() == pId).collect(Collectors.toList());
        //後輩中的非子類
        List<Department> successor = departmentList.stream().filter(x -> x.getParentId() != pId).collect(Collectors.toList());
        children.forEach(x ->
                {
                    makeTree(successor, x.getId()).forEach(
                            y -> x.getChildren().add(y)
                    );
                }
        );
        return children;
    }
    
}