Convert a Java Future to a Scala Future
For those reading this question now, if you're using Scala 2.13 and above, use:
import scala.jdk.FutureConverters._
And convert using completableFuture.asScala
If you're using Scala 2.12 and below, use
import scala.compat.java8.FutureConverters._
And convert using: toScala(completableFuture)
or completableFuture.toScala
Also, in Scala 2.12 make sure you're using the correct artifact:
org.scala-lang.modules:scala-java8-compat_2.12:0.9.0
Now, if for some reason what you have is actually a Future
and not CompletableFuture
, which should be a rare case nowadays, please follow first one of those answers: Transform Java Future into a CompletableFuture
Starting Scala 2.13
, the standard library includes scala.jdk.FutureConverters
which provides Java to Scala CompletableFuture/Future
implicit conversions:
import scala.jdk.FutureConverters._
// val javaFuture = java.util.concurrent.CompletableFuture.completedFuture(12)
val scalaFuture = javaFuture.asScala
// scalaFuture: scala.concurrent.Future[Int] = Future(Success(12))
How about just wrapping it (I'm assuming there's an implicit ExecutionContext here):
val scalaFuture = Future {
javaFuture.get
}
EDIT:
A simple polling strategy could look like this (java.util.Future => F):
def pollForResult[T](f: F[T]): Future[T] = Future {
Thread.sleep(500)
f
}.flatMap(f => if (f.isDone) Future { f.get } else pollForResult(f))
This will check if the Java future is done every 500ms. Obviously the total blocking time is the same as above (rounded up to the nearest 500ms) but this solution will allow other tasks to be interleaved in the same thread of the ExecutionContext
.