java 实现递归实现tree

package app.util;

import java.util.ArrayList;
import java.util.List;

import com.alibaba.fastjson.JSON;

public class Menu {
        private Integer pid;
        private String menuName;
        private Integer parentId;
        private Integer position;
        private List<Menu> childMenu;

        public Integer getPid() {
            return pid;
        }

        public void setPid(Integer pid) {
            this.pid = pid;
        }

        public String getMenuName() {
            return menuName;
        }

        public void setMenuName(String menuName) {
            this.menuName = menuName;
        }

        public Integer getParentId() {
            return parentId;
        }

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

        public Integer getPosition() {
            return position;
        }

        public void setPosition(Integer position) {
            this.position = position;
        }

        public List<Menu> getChildMenu() {
            return childMenu;
        }

        public void setChildMenu(List<Menu> childMenu) {
            this.childMenu = childMenu;
        }

        public Menu(Integer parentId,String menuName, Integer pid, Integer position) {
            super();
            this.parentId = parentId;
            this.menuName = menuName;
            this.pid = pid;
            this.position = position;
        }

        public Menu() {
            super();
        }

        public static void main(String[] args) {

            List<Menu> list=new ArrayList<Menu>();
            Menu menu1=new Menu(, "父级1", , );
            Menu menu2=new Menu(, "父级2", , );
            Menu menu1_1=new Menu(, "子级1_1", , );
            Menu menu1_2=new Menu(, "子级1_2", , );
            Menu menu1_2_1=new Menu(, "子级1_2_1", , );
            Menu menu1_2_2=new Menu(, "子级1_2_2", , );
            list.add(menu1);
            list.add(menu2);
            list.add(menu1_1);
            list.add(menu1_2);
            list.add(menu1_2_1);
            list.add(menu1_2_2);

            List<Menu> listTree=buildTree(list,);

            String trssJson=JSON.toJSONString(listTree);
            System.out.println(trssJson);

        }

        public static List<Menu> buildTree(List<Menu> list,int pid){
            List<Menu> menus=new ArrayList<Menu>();
            for (Menu menu : list) { 

                int parentId = menu.getPid();
                int  menuId= menu.getParentId();
                if (pid == parentId) {
                List<Menu> menuLists = buildTree(list, menuId); 

                menu.setChildMenu(menuLists);
                menus.add(menu);
            }
        } 

        return menus;
        }
}

成型

[
    {
        "childMenu": [
            {
                "childMenu": [

                ],
                "menuName": "子级1_1",
                "parentId": ,
                "pid": ,
                "position":
            },
            {
                "childMenu": [
                    {
                        "childMenu": [

                        ],
                        "menuName": "子级1_2_1",
                        "parentId": ,
                        "pid": ,
                        "position":
                    }
                ],
                "menuName": "子级1_2",
                "parentId": ,
                "pid": ,
                "position":
            }
        ],
        "menuName": "父级1",
        "parentId": ,
        "pid": ,
        "position":
    },
    {
        "childMenu": [
            {
                "childMenu": [

                ],
                "menuName": "子级1_2_2",
                "parentId": ,
                "pid": ,
                "position":
            }
        ],
        "menuName": "父级2",
        "parentId": ,
        "pid": ,
        "position":
    }
]