我怎样才能结合两个Future [JsArray]？

Question

I have two Future[JsArray] , f1 and f2 , and I need to wait that both are completed with a result.

If they both succeed, the final result should be a Success holding the sum of their contents. If at least one of then fails, the final result should be a Failure .

How can I do that?

Answer 1

You can combine futures using 'for' syntax. Something like:

val f1:Future[Int] = getF1()
val f2:Future[Int] = getF2()
val res:Future[Int] = for (
  v1 <- f1;
  v2 <- f2
) yield (v1 + v2)

Answer 2

Straight forward and simple solution

Future supports zip operation which is very handy.

val f1: Future[JsArray]
val f2: Future[JsArray]
val resultF = f1.zip(f2).map {case (a, b) =>  a ++ b}

if f1 or f2 fails, resultF will also fail with the same exception of f1 or f2 failure.

optionally you could remove parenthesis

val resultF = f1 zip f2 map { case (f1Result, f2Result) => f1Result ++ f2Result }

Answer 3

Assuming that by "summing arrays" you mean concatenating them with ++ , you are looking to do:

Future.sequence(Set(getF1,getF2)) map { _ reduce(_ ++ _)}

The sequence will succeed if and only if all futures succeed. Then we reduce the resulting Set by ++ -ing all its elements.

Answer 4

One solution

1. Define a map2 function for Future s:

    def map2[A, B, C](fa: Future[A], fb: Future[B])(g: (A, B) => C) (implicit executor: ExecutionContext): Future[C] = for { a <- fa b <- fb } yield g(a, b) 

2. Define a merge function for merging the two JsArray s (ie extracting and concatenating the elements , and use the result to create a new JsArray ):

    def merge(array1: JsArray, array2: JsArray): JsArray = JsArray(array1.elements ++ array2.elements: _*) 

   Note: you need the type ascription in order to pass the resulting Vector to JsArray 's apply method .

3. Call

    map2(f1, f2)(merge) 

Trial run in the REPL

scala> import spray.json._
import spray.json._

scala> import scala.concurrent.Future
import scala.concurrent.Future

scala> import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.ExecutionContext.Implicits.global

scala> val f1 = Future(JsArray(JsNumber(1), JsNumber(2))) 
f1: scala.concurrent.Future[spray.json.JsArray] = List()

scala> val f2 = Future(JsArray(JsNumber(3), JsNumber(4), JsNumber(5)))
f2: scala.concurrent.Future[spray.json.JsArray] = List()

scala> map2(f1, f2)(merge).onComplete(println)
Success([1,2,3,4,5])