Question

我需要使用Java 8将<String, List<String>>映射到Map<String,String>，并假定值是唯一的。例如，

输入图-

{"Fruit" -> ["apple","orange"], "Animal" -> ["Dog","Cat"]}

输出图

{"apple" -> "Fruit", "orange" -> "Fruit", "Dog"->"Animal", "Cat" -> "Animal"}

Map <String, String> outputMap = new HashMap<>();
for (Map.Entry<String, List<String>> entry : inputMap.entrySet()) {
    entry.getValue().forEach(value -> outputMap.put(value, entry.getKey()));
}

这是对的吗？我们可以使用Java 8流实现这一点吗？

Answer 1

这样做：

public class InverterMap {
    public static void main(String[] args) {

        Map<String, List<String>> mp = new HashMap<String, List<String>>();
        mp.put("Fruit", Arrays.asList("Apple", "Orange"));
        mp.put("Animal", Arrays.asList("Dog", "Cat"));
        System.out.println(mp);  // It returned {Fruit=[Apple, Orange], Animal=[Dog, Cat]}

        Map<String, String> invertMap = mp.entrySet().stream().collect(HashMap::new,
            (m, v) -> v.getValue().forEach(k -> m.put(k, v.getKey())), Map::putAll);

        System.out.println(invertMap);// It returned {Apple=Fruit, Cat=Animal, Orange=Fruit, Dog=Animal}

    }

}

阅读Stream.collect(Supplier supplier, BiConsumer, BiConsumer combiner)了解更多信息。

Answer 2

您可以这样尝试

Map <String, String> updatedMap = new HashMap<>();
oldMap.keySet()
      .forEach(i -> oldMap.get(i)
                          .forEach(k -> updatedMap.put(k, i)));

使用Java 8反转Map <String，List <String >>

2 个答案: