Question

正在寻找一种简单的方法来收集KeyAndValues having fields - String and List<T>到ImmutableListMultimap<String,T>的集合？试图做类似的事情，

 Collector.of(
          ImmutableListMultimap.Builder::new,
          ImmutableListMultimap.Builder<String,List<T>>::putAll,
          (b1, b2) -> b1.putAll(b2.build()),
          (builder) -> builder.build());

putAll需要Key，List<T>。我不知道如何在组合器中实现这一点。

编辑：

 @Value(staticConstructor = "of")
 private static class KeyAndValues<T> {

    private final String key;
    private final List<T> values;
}

Answer 1

不确定KeyAndValues<T>上可用的方法，但是这个怎么样？

  public static <T> Collector<KeyAndValues<T>,
                              ImmutableListMultimap.Builder<String, T>, 
                              ImmutableListMultimap<String, T>> toImmutableMultimap()
  {
    return Collector.of(
        ImmutableListMultimap.Builder::new,
        (b, kav) -> b.putAll(kav.getKey(), kav.getValues()),
        (builder1, builder2) -> builder1.putAll(builder2.build()),
        (builder) -> builder.build());
  }

或者，如果您希望隐藏累加器详细信息，可以使用以下内容：

public static <T> Collector<KeyAndValues<T>,
                            ?,
                            ImmutableListMultimap<String, T>> toImmutableMultimap()
{
  return Collector.of(
    ImmutableListMultimap.Builder<String, T>::new,
    (b, kav) -> b.putAll(kav.getKey(), kav.getValues()),
    (builder1, builder2) -> builder1.putAll(builder2.build()),
    (builder) -> builder.build());
}

Java 8 Collector for Guava的ImmutableListMultimap <string，t>

1 个答案: