JAVA8 List 分组按条件筛选

最新推荐文章于 2025-06-22 15:40:21 发布

calefaction_2015

最新推荐文章于 2025-06-22 15:40:21 发布

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分类专栏： Java_8

本文链接：https://blog.youkuaiyun.com/maguoliang110/article/details/86538207

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本文介绍如何使用 Java 的 Stream API 进行数据分组、筛选和聚合操作，通过实例演示了如何从列表中找出特定条件下的元素，并按需进行分组和筛选，获取最高价元素等复杂需求。

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import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.serializer.SerializerFeature;

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

public class ListGroupFindFirstTest3 {
    public static void main(String[] args) {
        List<Person> couponList = new ArrayList<>();
        Person person1 = new Person(1,10000,"tom");
        Person person2 = new Person(2,20000,"ketty");
        Person person3 = new Person(3,30000,"jerry");
        Person person4 = new Person(3,40000,"lilei");
        couponList.add(person1);
        couponList.add(person2);
        couponList.add(person3);
        couponList.add(person4);

        //1 list分组筛选
        Map<Integer, List<Person>> resultList1 = couponList.stream().collect(
                Collectors.groupingBy(Person::getCardno));
        //2 list筛选 取分组内的第一值
        Map<Integer, Person> resultList =
                couponList.stream().collect(
                        Collectors.groupingBy(Person::getCardno,
                                //包装后的收集器
                                Collectors.collectingAndThen(Collectors.toList(), value->value.get(0))));
        //3  list筛选 取分组内根据条件筛选 price最高的一个
        Map<Integer, Person> resultList2 =
                couponList.stream().collect(
                        Collectors.groupingBy(Person::getCardno,
                                Collectors.collectingAndThen(
                                        Collectors.maxBy(Comparator.comparingInt(Person::getSalary)), Optional:: get))

                );

        //SerializerFeature.PrettyFormat JSON格式化输出

        System.out.println(JSON.toJSONString(resultList2, SerializerFeature.PrettyFormat));;

    }
}
class Person {
    private Integer cardno;
    private Integer salary;
    private String name;

    public Person(Integer cardno, Integer salary, String name) {
        this.cardno = cardno;
        this.salary = salary;
        this.name = name;
    }

    public Integer getCardno() {
        return cardno;
    }

    public void setCardno(Integer cardno) {
        this.cardno = cardno;
    }

    public Integer getSalary() {
        return salary;
    }

    public void setSalary(Integer salary) {
        this.salary = salary;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}