java遞歸獲取某個父節點下面的所有子節點

package com.demo.web.test;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

import com.demo.web.model.Menu;
import com.google.gson.Gson;

public class Test7 {
    private static List<Menu> treeList = new ArrayList<>();  //全局變量

    public static void main(String[] args) {
//        List<Menu> menuList=new ArrayList<Menu>();
        List<Menu> pidList=new ArrayList<Menu>();
        Menu mu=new Menu();
        mu.setId(1);
        pidList.add(mu);
        mu.setName("目錄");
        mu.setParentid("0");
        Menu mu1=new Menu();
        mu1.setId(2);
        mu1.setName("目錄1");
        mu1.setParentid("1");
        Menu mu2=new Menu();
        mu2.setId(3);
        mu2.setName("目錄2");
        mu2.setParentid("1");
        Menu mu3=new Menu();
        mu3.setId(4);
        mu3.setName("目錄3");
        mu3.setParentid("1");
        
        //目錄3下子節點
        Menu mu4=new Menu();
        mu4.setId(5);
        mu4.setName("目錄4");
        mu4.setParentid("4");
        
        treeList.add(mu);
        treeList.add(mu1);
        treeList.add(mu2);
        treeList.add(mu3);
        treeList.add(mu4);
        //pid
        System.out.println("pidList:-------------------"+pidList);
        List<Menu> tree = getTree(treeList,pidList);
        for (Menu menu : tree) {
            System.out.println(menu.getId()+" ------- "+menu.getName()+"  "+menu.getChildren().get(2).getChildren());
        }
        
        System.out.println("7715-=-----------"+tree.get(0).getChildren());
        Gson gson = new Gson();//import com.google.gson.Gson;
        String result = gson.toJson(tree);//pojo
        System.out.println("我看看0---------"+result);
    }
    
    
    public static List<Menu> getTree(List<Menu> menu,List<Menu> parentList) {
        //先獲取到所有數據
//        treeList=MenuMapper.getList();   
        if(menu==null) return null;

        //獲取到所有一級節點
//        List<Menu> parentList = this.MenuMapper.findParentList();
        List<Menu> list = new ArrayList<>();
        if(parentList != null){
            for (int i = 0; i < parentList.size(); i++) {
                list.add(recursiveTree(parentList.get(i).getId()));
            }
        }
        return list;
    }


    /**
     * 遞歸算法解析成樹形結構
     * @param cid
     */
    public static Menu recursiveTree(Integer cid) {
        Menu node = getMenuById(cid);
        List<Menu> childTreeNodes  = getChildTreeById(cid);
        for(Menu child : childTreeNodes){
            Menu n = recursiveTree(child.getId());
            List<Menu> list = new ArrayList<Menu>();
            list.add(n);
            System.out.println(node.getChildren());
            if (node.getChildren()==null) {
                List<Menu> li = new ArrayList<Menu>();
                node.setChildren(li);
            }
//            node.setChildren(list);
            node.getChildren().add(n);
        }
        return node;
    }

    /**
     * 根據CID查詢節點對象
     */
    public static Menu getMenuById(Integer cid){
        Map map =  getTreeMap();
        return (Menu) map.get(cid);
    }

    /**
     * 一次性取所有數據，為了減少對數據庫查詢操作
     * @return
     */
    public static Map getTreeMap(){
        Map map =  new HashMap<Integer, Menu>();
        if(null != treeList){
            for(Menu d : treeList){
                map.put(d.getId(), d);
            }
        }
        return map;
    }

    /**
     * 根據父節點CID獲取所有了節點
     */
    public static List<Menu> getChildTreeById(Integer cid){
        List<Menu> list = new ArrayList<>();
        if(null != treeList){
            for (Menu d : treeList) {
                if(null != cid){
                    if (cid.equals(Integer.valueOf(d.getParentid()))) {
                        list.add(d);
                    }
                }
            }
        }
        return list;
    }
}