[英]Java 8 Collector for Guava's ImmutableListMultimap<String,T>
尋找一種簡單的方法來收集KeyAndValues having fields - String and List<T>
到ImmutableListMultimap<String,T>
的KeyAndValues having fields - String and List<T>
集合嗎? 試圖做類似的事情,
Collector.of(
ImmutableListMultimap.Builder::new,
ImmutableListMultimap.Builder<String,List<T>>::putAll,
(b1, b2) -> b1.putAll(b2.build()),
(builder) -> builder.build());
putAll
采用Key
, List<T>
。 我不確定如何在合並器中實現這一點。
編輯:
@Value(staticConstructor = "of")
private static class KeyAndValues<T> {
private final String key;
private final List<T> values;
}
不確定KeyAndValues<T>
上可用的方法,但是如何呢?
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,如果您希望隱藏累加器詳細信息,則可以使用以下方法:
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());
}
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