stream流 groupby后排序

对于流（Stream）对象，你可以使用`groupingBy`方法对其进行分组，然后使用`sorted`方法对每个组进行排序。下面是一个示例代码：

import java.util.Comparator;
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 = List.of(
                new Person("Alice", 25),
                new Person("Bob", 30),
                new Person("Charlie", 20),
                new Person("Dave", 25),
                new Person("Eve", 30)
        );

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

        groupedByAge.forEach((age, group) -> {
            System.out.println("Age: " + age);
            System.out.println("Group: " + group);
            List<Person> sortedGroup = group.stream()
                    .sorted(Comparator.comparing(Person::getName))
                    .collect(Collectors.toList());
            System.out.println("Sorted Group: " + sortedGroup);
        });
    }

    static class Person {
        private