Scala 2.8.1 implicitly convert to java.util.List<java.util.Map<String, Object>>

Question

I have a Scala data structure created with the following:

List(Map[String, Anyref]("a" -> someFoo, "b" -> someBar))

I would like to implicitly convert it (using scala.collection.JavaConversions or scala.collection.JavaConverters) to a java.util.List<java.util.Map<String, Object>> to be passed the a Java method that expects the latter.

Is this possible?

I have already created the following method that does it, but was wondering if it can be done automatically by the compiler?

import scala.collection.JavaConversions._
def convertToJava(listOfMaps: List[Map[String, AnyRef]]):
  java.util.List[java.util.Map[String, Object]] = {
  asJavaList(listOfMaps.map(asJavaMap(_)))
}

Landei · Accepted Answer · 2010-12-20 14:02:51Z

4

How about writing

implicit def convertToJava...

?

answered Dec 20, 2010 at 14:02

Landei

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2 Comments

Ralph Over a year ago

That makes sense, but I was hoping that Scala would do it automatically so I could save 4 lines of code :-).

Landei Over a year ago

This is a quite special case, so I think these 4 lines are okay. Generally over-the-top use of implicit conversion can lead to surprising results, so it's only sensible that the Scala library uses them with caution.

psp · Accepted Answer · 2010-12-21 05:28:39Z

4

You don't want this kind of multilevel conversion happening by magic. You can improve a little on your own conversion though, at least aesthetically.

import java.{ util => ju }
implicit def convert[K, V](xs: List[Map[K, V]]): ju.List[ju.Map[K, V]] = xs map (x => x: ju.Map[K, V])

answered Dec 21, 2010 at 5:28

psp

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3 Comments

Esko Over a year ago

I'm giving you an upvote just for the import aliasing line - didn't know one could do that!

Ralph Over a year ago

Thanks. I'll take a look at your solution.

Ralph Over a year ago

@Esko: I've started using the import aliasing to rename java.* classes: import java.lang.{Integer => JInteger} for those rare cases where I have to force autoboxing: (x: JInteger).

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