将 Java 映射转换为 Scala 映射 [英] Convert Java Map to Scala Map

问题描述

我有一个 java 映射:java.util.Map>我想将其转换为 Scala 地图:Map[SomeObject, Set[OtherObject]]

I have a java map: java.util.Map<SomeObject, java.util.Collection<OtherObject>> and I would like to convert it to the scala map: Map[SomeObject, Set[OtherObject]]

我用过 ma​​pAsScalaMap 但结果不是我想要的，结果是:Map[SomeObject, java.util.Collection[OtherObject]].如何修复它以将集合转换为集合?

I have used mapAsScalaMap but the result is not quite what I want, the result is: Map[SomeObject, java.util.Collection[OtherObject]]. How can I fix it to also convert the collection to a set?

注意:实际上我最初的问题是将谷歌的 ArrayListMultimap 转换为 MultiMap[SomeObject, OtherObject] 但由于这是不可能的，我已经拆分问题.如果你有原始问题的解决方案，我也会接受它作为答案.

NOTE: actually my original problem was to convert google's ArrayListMultimap<SomeObject, OtherObject> to a MultiMap[SomeObject, OtherObject] but since this was not possible I've split the problem. If you have a solution for the original problem, I'll also accept it as the answer.

推荐答案

Edit:现在推荐的方式是使用 JavaConverters 和 .asScala方法:

Edit: the recommended way is now to use JavaConverters and the .asScala method:

import scala.collection.JavaConverters._
val myScalaMap = myJavaMap.asScala.mapValues(_.asScala.toSet)

这样做的优点是不使用神奇的隐式转换，而是显式调用 .asScala，同时保持干净和简洁.

This has the advantage of not using magical implicit conversions but explicit calls to .asScala, while staying clean and consise.

JavaConversions 的原始答案:

The original answer with JavaConversions:

您可以使用 scala.collection.JavaConversions 在 Java 和 Scala 之间进行隐式转换:

You can use scala.collection.JavaConversions to implicitly convert between Java and Scala:

import scala.collection.JavaConversions._
val myScalaMap = myJavaMap.mapValues(_.toSet)

调用 mapValues 会触发从 java Map 到 scala Map 的隐式转换，然后调用 toSet> 在 java 集合上隐式转换为 Scala 集合，然后转换为 Set.

Calling mapValues will trigger an implicit conversion from the java Map to a scala Map, and then calling toSet on the java collection with implicitly convert it to a scala collection and then to a Set.

默认情况下，它返回一个可变的Map，你可以通过额外的.toMap获得一个不可变的.

By default, it returns a mutable Map, you can get an immutable one with an additional .toMap.

简短的例子:

scala> val a: java.util.Map[String, java.util.Collection[String]] = new java.util.HashMap[String, java.util.Collection[String]]
a: java.util.Map[String,java.util.Collection[String]] = {}

scala> val b = new java.util.ArrayList[String]
b: java.util.ArrayList[String] = []

scala> b.add("hi")
res5: Boolean = true

scala> a.put("a", b)
res6: java.util.Collection[String] = []

scala> import scala.collection.JavaConversions._
import scala.collection.JavaConversions._

scala> val c = a.mapValues(_.toSet)
c: scala.collection.Map[String,scala.collection.immutable.Set[String]] = Map(a -> Set(hi))

scala> c.toMap
res7: scala.collection.immutable.Map[String,scala.collection.immutable.Set[String]] = Map(a -> Set(hi))

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