如何将map流分组到Map<String、Map<String、String>>？

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

public class Main {
    public static void main(String[] args) {
        // 假设有一个包含需要分组的数据的map流
        Map<String, Map<String, String>> mapStream = new HashMap<>();
        mapStream.put("group1", createInnerMap("key1", "value1"));
        mapStream.put("group1", createInnerMap("key2", "value2"));
        mapStream.put("group2", createInnerMap("key3", "value3"));
        mapStream.put("group2", createInnerMap("key4", "value4"));
        mapStream.put("group3", createInnerMap("key5", "value5"));

        // 使用Stream API和Collectors.groupingBy()方法进行分组
        Map<String, Map<String, String>> groupedMap = mapStream.entrySet().stream()
                .collect(Collectors.groupingBy(Map.Entry::getKey, Collectors.toMap(
                        entry -> entry.getValue().keySet().iterator().next(),
                        entry -> entry.getValue().values().iterator().next()
                )));

        // 打印分组结果
        for (Map.Entry<String, Map<String, String>> entry : groupedMap.entrySet()) {
            System.out.println("Group: " + entry.getKey());
            System.out.println("Inner Map: " + entry.getValue());
        }
    }

    // 创建内部map的辅助方法
    private static Map<String, String> createInnerMap(String key, String value) {
        Map<String, String> innerMap = new HashMap<>();
        innerMap.put(key, value);
        return innerMap;
    }
}