ListenableFuture to scala Future

future, scala

Solution

The second option is best, it keeps everything asynchronous. but... you can do one better and abstract the solution into a reusable pattern:

implicit class RichListenableFuture[T](lf: ListenableFuture[T]) {
  def asScala: Future[T] = {
    val p = Promise[T]()
    Futures.addCallback(lf, new FutureCallback[T] {
      def onFailure(t: Throwable): Unit = p failure t
      def onSuccess(result: T): Unit    = p success result
    })
    p.future
  }    
}

You can then simply call:

executor.asyncExecute(query).asScala

Problem

I am in the process of writing a small scala wrapper around a java library. The java library has an object QueryExecutor exposing 2 methods: - execute(query): Result - asyncExecute(query): ListenableFuture[Result] ListenableFuture in this context is the one from the guava library. I want my scala wrapper to return a Future[Result] instead of the java object, but I am not sure what is the best way to implement that. Here are 2 solutions I came up with: ``` future { executor.execute(query) } ``` and ``` val p = promise[Result] val guavaFuture = executor.asyncExecute(query) Futures.addCallback(guavaFuture, new FutureCallback[Result] { def onFailure(t: Throwable) { p.failure(t) } def onSuccess(result: Result) { p.success(result) } }) p.future ``` I am wondering which method is the best. My intuition is that the first one, while returning a Future, will still block a thread while the call to execute waits for a response, the second one looks like it should be really non blocking. Any comment on the pros/cons of each method ?

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