I have a java map: java.util.Map> and I would like to convert it to the scala map: Map[SomeObject, Set[OtherObject]]
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?
NOTE: actually my original problem was to convert google's ArrayListMultimap 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.
Edit: the recommended way is now to use JavaConverters and the .asScala method:
import scala.collection.JavaConverters._ val myScalaMap = myJavaMap.asScala.mapValues(_.asScala.toSet)
This has the advantage of not using magical implicit conversions but explicit calls to .asScala, while staying clean and consise.
The original answer with JavaConversions:
You can use scala.collection.JavaConversions to implicitly convert between Java and Scala:
import scala.collection.JavaConversions._ val myScalaMap = myJavaMap.mapValues(_.toSet)
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.
By default, it returns a mutable Map, you can get an immutable one with an additional .toMap.
Short-ish example:
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))
You can convert the Java Map into Scala Map using the below function:
val scalaMap = javaMap.asScala;
For using this you need to import the import scala.collection.JavaConverters._ library.
Hope this helps.
Immutable Map myJavaMap.asScala.toMap
Mutable Map myJavaMap.asScala
