JAVA List 用steam 实现两个字段的分组并求和

使用JDK8 的Steam来对实体类User（ id,age,count）的两个字段（id,age）进行分组，并对分组之后的count 字段进行求和，代码如下：

实现逻辑主要在测试类Test3 的gruopAndSumCount 里

package com.shitouda;

/**
 * @Description: 一个测试类
 * @Author shitouda
 * @Date 2021-04-19 20:49
 */
public class User {
    private Integer id;
    private Integer age;
    private Integer count;

    public User() {
    }

    public User(Integer id, Integer age, Integer count) {
        this.id = id;
        this.age = age;
        this.count = count;
    }

    public Integer getId() {
        return id;
    }

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

    public Integer getAge() {
        return age;
    }

    public void setAge(Integer age) {
        this.age = age;
    }

    public Integer getCount() {
        return count;
    }

    public void setCount(Integer count) {
        this.count = count;
    }

}

package com.shitouda;

import java.util.ArrayList;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Collectors;

/**
 * @Description: TODO
 * @Author shitouda
 * @Date 2021-04-19 20:50
 */
public class Test3 {

    public List<User> gruopAndSumCount(List<com.shitouda.User> users){
        Map<String, IntSummaryStatistics> collect = users.parallelStream()
                .collect(Collectors.groupingBy(
                        a -> a.getId() + "_" + a.getAge(), Collectors.summarizingInt(a -> a.getCount()))
                );

        List<User> users1 = new ArrayList<>();
        collect.forEach((key,value) ->{
            User user = new User();
            String[] idAgeArr = key.split("_");
            user.setId(Integer.valueOf(idAgeArr[0]));
            user.setAge(Integer.valueOf(idAgeArr[1]));
            Integer count = Math.toIntExact(value.getSum());
            user.setCount(count);
            users1.add(user);
        });
        return users1;
    }

    public static void main(String[] args) {
        List<User> users = new ArrayList<>();
        User user1 = new User(1,1,3);
        User user2 = new User(1,1,5);
        User user3 = new User(2,1,5);
        User user4 = new User(2,1,2);
        User user5 = new User(2,1,2);
        User user6 = new User(3,3,2);
        users.add(user1);
        users.add(user2);
        users.add(user3);
        users.add(user4);
        users.add(user5);
        users.add(user6);
        Test3 test3 = new Test3();
        List<User> list = test3.gruopAndSumCount(users);
        System.out.println(list);
    }
}

测试结果：