Nested Java hashmap to nested Scala map conversion

Question

What is the right way to convert a variable of type java.util.HashMap<java.lang.String, java.util.List<java.lang.String>> in Java, to its Scala equivalent: Map[Map[String, List[String]]]? (with Scala Map, String and List)

I tried to use import scala.collection.JavaConverters._ and do JavaNestedMap.asScala but it failed. Is there a smart way of doing this (rather than having two maps)?

Daenyth · Accepted Answer · 2015-07-01 12:28:18Z

2

There's no single call way I know of.

This is succinct likely inefficient in a hot loop. Profile if it ends up being too slow and then you'd want to use builders directly.

val in: JMap[JMap[String, String]] = ???
val out: Map[Map[String, String]] = in.asScala.mapValues(_.asScala)
val again: JMap[JMap[String, String]] = out.map(_.asJava).asJava

It's worth noting that .asScala gives you a mutable map for consistency with the java map. If you want to get an immutable map back, you need to call .toMap afterwords.

edited Jul 1, 2015 at 12:28

answered Jul 1, 2015 at 0:40

Daenyth

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Daniel Over a year ago

Thanks for comment. Though I think it is better to write the last two steps like this: in.asScala.map{item => (item._1, item._2.asScala.toMap)}.toMap . toMap is to convert it to Scala's immutable map.

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