使用比较器的Java8 streams groupingBy

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

public class GroupingByExample {
    public static void main(String[] args) {
        List<String> fruits = Arrays.asList("apple", "banana", "orange", "grape", "kiwi");

        // 按照首字母分组并排序
        Map<Character, List<String>> groupedFruits = fruits.stream()
                .collect(Collectors.groupingBy(s -> s.charAt(0), Collectors.toList()));

        // 按照首字母分组并按照长度排序
        Map<Character, List<String>> sortedGroupedFruits = fruits.stream()
                .collect(Collectors.groupingBy(s -> s.charAt(0), Collectors.toList()));

        Comparator<String> byLength = Comparator.comparing(String::length);
        sortedGroupedFruits = fruits.stream()
                .collect(Collectors.groupingBy(s -> s.charAt(0), Collectors.toList(byLength)));

        System.out.println(groupedFruits);
        System.out.println(sortedGroupedFruits);
    }
}