Java - 是否有任何Stream收集器返回ImmutableMap？

本文介绍了Java - 是否有任何Stream收集器返回ImmutableMap？的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述 我发现自己想要一个 Collectors.toMap 的变体，它返回一个 ImmutableMap ，这样我就可以：I find myself wanting a variant of Collectors.toMap which returns an ImmutableMap, such that I can do:ImmutableMap result = list.stream().collect(MyCollectors.toImmutableMap( tuple -> tuple._1(), tuple -> tuple._2());（其中元组在这个特定的例子中是Scala Tuple2 ）(where tuple in this particular example is a Scala Tuple2)我刚刚学会了这样的方法将会带来Java-8支持在Guava 21（yay！）但这听起来好了6个月之后。有谁知道今天可能实现的任何现有库（等）？I've just learned that such a method will be coming with Java-8 support in Guava 21 (yay!) but that sounds a good 6 months away. Does anyone know of any existing libraries (etc) which might implement this today? ImmutableMap 并不是严格要求的，但似乎是我要求的最佳选择：按键查找，并保留原始迭代顺序。不变性也是首选。ImmutableMap is not strictly required but seems the best choice as I require: lookup by key, and retaining original iteration order. Immutability is always preferred too.请注意 FluentIterable.toMap（功能离子）是不够的，因为我既需要键映射功能，也需要值映射功能。Note that FluentIterable.toMap(Function) is not sufficient because I need both a key-mapping function as well as a value-mapping function.推荐答案您不需要为此收集器编写匿名类。您可以使用 Collector.of 代替：You don't need to write an anonymous class for this collector. You can use Collector.of instead:public static <T, K, V> Collector<T, ?, ImmutableMap<K,V>> toImmutableMap( Function<? super T, ? extends K> keyMapper, Function<? super T, ? extends V> valueMapper) { return Collector.of( ImmutableMap.Builder<K, V>::new, (b, e) -> b.put(keyMapper.apply(e), valueMapper.apply(e)), (b1, b2) -> b1.putAll(b2.build()), ImmutableMap.Builder::build);}或者如果您不介意首先将结果收集到可变地图中，然后将数据复制到不可变的映射中，您可以使用内置的 toMap 收集器与 collectAndThen ：Or if you don't mind collecting the results into a mutable map first and then copy the data into an immutable map, you can use the built-in toMap collector combined with collectingAndThen:ImmutableMap<String, String> result = list.stream() .collect(collectingAndThen( toMap( tuple -> tuple._1(), tuple -> tuple._2()), ImmutableMap::copyOf)); 这篇关于Java - 是否有任何Stream收集器返回ImmutableMap？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！