Java8将Map<K、List<V>>转换为Map<V、List<K>>

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

public class MapConverter {
    public static void main(String[] args) {
        // 原始的Map<K, List<V>>
        Map<String, List<Integer>> map = new HashMap<>();
        map.put("A", Arrays.asList(1, 2, 3));
        map.put("B", Arrays.asList(4, 5));
        map.put("C", Arrays.asList(6, 7, 8));

        // 转换为Map<V, List<K>>
        Map<Integer, List<String>> convertedMap = map.entrySet().stream()
                .flatMap(entry -> entry.getValue().stream().map(value -> new AbstractMap.SimpleEntry<>(value, entry.getKey())))
                .collect(Collectors.groupingBy(Map.Entry::getKey, Collectors.mapping(Map.Entry::getValue, Collectors.toList())));

        // 输出转换后的Map<V, List<K>>
        for (Map.Entry<Integer, List<String>> entry : convertedMap.entrySet()) {
            System.out.println(entry.getKey() + ": " + entry.getValue());
        }
    }
}

1: [A]
2: [A]
3: [A]
4: [B]
5: [B]
6: [C]
7: [C]
8: [C]