java - 如何使用流在 java 中生成列表的映射 (Map>>)

Question

给定:

enum Food{
FRUITS, VEGGIES;
}

Map<String, List<String>> basketMap = new HashMap<>();
basketMap .put("bucket1", Arrays.asList("apple", "banana"));
basketMap .put("bucket2", Arrays.asList("orange", "kiwi"));
basketMap .put("bucket3", Arrays.asList("banana", "orange"));

需要生成一个map of list的Map(populte FruitBaskerMap)

Map<String, Map<Food, List<String>> fruitBasketMap = new HashMap<>();

最终输出:

fruitBasketMap:
[
bucket1, [Food.FRUITS, {"apple", "banana"}],
bucket2, [Food.FRUITS, {"orange", "kiwi"}],
bucket3, [Food.FRUITS, {"banana", "orange"}]
]

我尝试了以下方法(但没有成功)

fruitBasketMap = basketMap.entrySet().stream().collect(
    Collectors.toMap(Map.Entry::getKey,
        Collectors.toMap(Food.FRUITS,
            Collectors.toList(Map.Entry::getValue())
        )
    )
);

有人可以告诉我该怎么做吗？

Answer 1

这个实现似乎有效(使用 Java 9 Map.of):

Map<String, Map<Food, List<String>>> fruitBasketMap = basketMap.entrySet().stream()
        .map(e -> Map.entry(e.getKey(), Map.of(Food.FRUITS, e.getValue())))
        .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));

测试输出:

{
bucket2={FRUITS=[orange, kiwi]}, 
bucket3={FRUITS=[banana, orange]}, 
bucket1={FRUITS=[apple, banana]}
}