[移动开发]List集合根据某个属性分组Java8

package com.tydic.portal;


import com.tydic.portal.sysmgr.po.User;
import com.tydic.portal.sysmgr.po.User2;
import org.junit.Test;

import java.util.*;
import java.util.stream.Collectors;

/**
 *
 * @description:
 * @author: ruansh
 * @date:
 * @version:
 */
public class TestMap {

    @Test
    public void testGroup(){
        ArrayList   arrayList1= new  ArrayList<Integer>();
        arrayList1.add(20);
        arrayList1.add(19);
        arrayList1.add(18);
        ArrayList   arrayList2= new  ArrayList<Integer>();
        arrayList2.add(20);
        ArrayList   arrayList3= new  ArrayList<Integer>();
        arrayList3.add(19);
        arrayList3.add(18);
        List<User2> users2 =Arrays.asList(new User2(arrayList1,"张三"),new User2(arrayList2,"李四"),new User2(arrayList3,"王五"));
        Map<Integer,List<User2>>  userMap =  new HashMap<>();
        users2.forEach(user->{
//            如果这里age是个集合；
            List<Integer> ages = user.getAge();
            for(Integer  age:ages){
                List<User2> users=userMap.get(age);
                if(users==null){
                    users = new ArrayList<>();
                    users.add(user);
                    userMap.put(age,users);
                }else{
                    users.add(user);
                    userMap.put(age,users);
                }
            }
        });
        userMap.forEach((x,y)->{
            System.out.println(x+":"+y);
        });
    }
}