CODEWITHSUNDEEP
scalafutureasynchttpclient
John
John

Reputation: 5364

convert `com.ning.http.client.ListenableFuture[Any]` into `scala.concurrent.Future[Any]`

Is there any way I can convert a variable of type com.ning.http.client.ListenableFuture[A] into a type scala.concurrent.Future[A]

in other words what would be the content of the function 

def toFuture[A](a: com.ning.http.client.ListenableFuture[A]):scala.concurrent.Future[A] = ???

I am specifically in the case where A = com.ning.http.client.Response

Note that com.ning.http.client.ListenableFuture[A] is not the same as com.google.common.util.concurrent.ListenableFuture (and hence this proposed duplicate does not solve the issue)

Upvotes: 0

Views: 438

Answers (1)

Sergey
Sergey

Reputation: 2900

The idea is the same as with guava's ListenableFuture, although a little more constrained due to more constrained signature.

First, you need to get a java.util.concurrent.Executor to add a callback. Since your Scala code interacts with a Java library, I'd suggest to define your pool of scala.concurrent.ExecutorServices based on Java Executors - that way you can retain both the instance of an Executor and an ExecutorService, something like the following:

import java.util.concurrent.Executors
import scala.concurrent.ExecutionContext
val executor = Executors.newFixedThreadPool(5) // use it for Java futures
implicit val executionContext = ExecutionContext.fromExecutor(executor) // use it for Scala futures

The above steps are not needed if you want to process everything in different pools. In case you want to use an existing ExecutionContext, here's a snippet I googled.

Then, to convert the ListenableFuture into a Future, I'd do something like this (considering some exception semantics of java.util.concurrent.Future):

def toFuture[A](a: ListenableFuture[A]): Future[A] = {
  val promise = Promise[A]()
  a.addListener(new Runnable {
    def run() = {
      try {
        promise.success(a.get)
      } catch {
        case ex: ExecutionException => promise.failure(ex.getCause)
        case ex => promise.failure(ex)
      }
    }
  }, executor)
  promise.future
}

Upvotes: 1

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