JAVA JDK8 List分组获取第一个元素的方法

package test;

import com.alibaba.fastjson.json;

import com.alibaba.fastjson.serializer.serializerfeature;

import java.util.arraylist;

import java.util.list;

import java.util.map;

import java.util.stream.collectors;

public class listgroupfindfirsttest3 {

   public static void main(string[] args) {

     list<coupon> couponlist = new arraylist<>();

     coupon coupon1 = new coupon( 1 , 100 , "优惠券1" );

     coupon coupon2 = new coupon( 2 , 200 , "优惠券2" );

     coupon coupon3 = new coupon( 3 , 300 , "优惠券3" );

     coupon coupon4 = new coupon( 3 , 400 , "优惠券4" );

     couponlist.add(coupon1);

     couponlist.add(coupon2);

     couponlist.add(coupon3);

     couponlist.add(coupon4);

     map<integer, coupon> resultlist = couponlist.stream().collect(collectors.groupingby(coupon::getcouponid,collectors.collectingandthen(collectors.tolist(),value->value.get( 0 ))));

     system.out.println(json.tojsonstring(resultlist, serializerfeature.prettyformat));

   }

}

package test;

public class coupon {

   private integer couponid;

   private integer price;

   private string name;

   public coupon(integer couponid, integer price, string name) {

     this .couponid = couponid;

     this .price = price;

     this .name = name;

   }

   public integer getcouponid() {

     return couponid;

   }

   public void setcouponid(integer couponid) {

     this .couponid = couponid;

   }

   public integer getprice() {

     return price;

   }

   public void setprice(integer price) {

     this .price = price;

   }

   public string getname() {

     return name;

   }

   public void setname(string name) {

     this .name = name;

   }

}