Getting data out of a Future in Scala

Question

I've a Future[List[Person]][1] and I want to get the List[Person] from it. How can I do it ?

import scala.concurrent.Future
val futPersons : Future[List[Person]] = .... 

Answer 1

There are multiple ways:

futPersons.map { personList =>
  ....
}

This map returns another Future composed with whatever you return from the map. The map will execute only if the future completes successfully. If you need to handle failure you can use onComplete

futPersons.onComplete {
  case Success(personList) => ...
  case Failure(exception)  =>  ... 
}

Or you can wait for the future to complete (this is blocking):

val personList: List[Person] = Await.result(futPersons, 1 minutes)

Answer 2

Blocking way (pauses your thread until you get the value back) using Await.result:

scala.concurrent.Await.result(futPersons, timeout)

Or, using a callback with onSuccess:

futPersons onSuccess {
    case persons => // do something with persons
}