scala.concurrent.Future wrapper for java.util.concurrent.Future

Question

I'm using Play Framework 2.1.1 with an external java library that produces a java.util.concurrent.Future result. I'm using the scala future's as opposed to Akka which I think is the right thing to do as of Play 2.1. How can I wrap the java.util.concurrent.Future up into a scala.concurrent.Future while still keeping the code non-blocking?

def geConnection() : Connection = {
  // blocking with get
  connectionPool.getConnectionAsync().get(30000, TimeUnit.MILLISECONDS)
}

The above code returns a connection but uses a get so it becomes blocking

def getConnectionFuture() : Future[Connection] = {
  future {
    // how to remove blocking get and return a scala future?
    connectionPool.getConnectionAsync().get(30000, TimeUnit.MILLISECONDS)
  }
}

Ideally I want a scala function that returns the connection as a future like the code above but without the code blocking via the get. What else do I need to put into the function to make it non blocking.

Any pointers would be great.

Answer 1

import java.util.concurrent.{Future => JFuture}
import scala.concurrent.{Future => SFuture}

You can't wrap JFuture with SFuture without blocking since there is a callback in SFuture (onComplete) and there is only blocking get in JFuture.

All you can do is to create additional thread and block it with get, then complete Promise with result of get.

val jfuture: JFuture[T] = ???
val promise = Promise[T]()
new Thread(new Runnable { def run() { promise.complete(Try{ jfuture.get }) }}).start
val future = promise.future

You could check isDone in endless loop, but I don't think it is better then blocking.