在Java8中使用列表值Map<Key、List<Value>> to Map <Value、Key>进行映射

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

public class MapConversion {
    public static void main(String[] args) {
        // 原始的Map<Key, List<Value>>
        Map<String, List<Integer>> originalMap = new HashMap<>();
        originalMap.put("Key1", Arrays.asList(1, 2, 3));
        originalMap.put("Key2", Arrays.asList(2, 3, 4));
        originalMap.put("Key3", Arrays.asList(5));

        // 转换后的Map<Value, Set<Key>>，使用Set来避免键重复
        Map<Integer, Set<String>> convertedMap = originalMap.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.toSet())
            ));

        // 打印转换后的Map
        convertedMap.forEach((value, keys) -> System.out.println(value + " -> " + keys));
    }
}