具有自定义密钥名称的Collectors.groupingBy

import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<Person> persons = Arrays.asList(
                new Person("John", 25),
                new Person("Jane", 30),
                new Person("Tom", 25),
                new Person("Alice", 30)
        );

        Map<Integer, List<Person>> ageGroups = persons.stream()
                .collect(Collectors.groupingBy(Person::getAge, Collectors.toList()));

        System.out.println(ageGroups);
    }

    static class Person {
        private String name;
        private int age;

        public Person(String name, int age) {
            this.name = name;
            this.age = age;
        }

        public String getName() {
            return name;
        }

        public int getAge() {
            return age;
        }

        @Override
        public String toString() {
            return name;
        }
    }
}