将HashMap从Map <String,Boolean>反转为Map <Boolean,List <String >>

Question

是否有更优雅/内置的方式来反转Hashmap的键和值？

我目前有以下内容.

private Map<Boolean, List<String>> reverseMap(Map<String, Boolean> permissions) {
    List<String> allow = new ArrayList<String>();
    List<String> deny = new ArrayList<String>();
    Map<Boolean, List<String>> returnvalue = new HashMap<Boolean, List<String>>();

    for (Entry<String, Boolean> entry : permissions.entrySet()) {
        if(entry.getValue()) {
            allow.add(entry.getKey());
        } else {
            deny.add(entry.getKey());
        }
    }

    returnvalue.put(true, allow);
    returnvalue.put(false, deny);
    return returnvalue;
}

Answer 1

您可以考虑使用Guava的一个Multimap实现.例如:

private Multimap<Boolean, String> reverseMap(Map<String, Boolean> permissions) {
   Multimap<Boolean, String> multimap = ArrayListMultimap.create();
   for (Map.Entry<String, Boolean> entry : permissions.entrySet()) {
      multimap.put(entry.getValue(), entry.getKey());
   }
   return multimap;
}

或者更一般地说:

private static <K, V> Multimap<V, K> reverseMap(Map<K, V> source) {
   Multimap<V, K> multimap = ArrayListMultimap.create();
   for (Map.Entry<K, V> entry : source.entrySet()) {
      multimap.put(entry.getValue(), entry.getKey());
   }
   return multimap;
}