Question

如果我的方法返回地图的未来，如下所示

 def getFutureMap(count:Int):Future[Map[Int, String]] = {

     Future {
         val m: scala.collection.mutable.Map[Int, String] = scala.collection.mutable.Map[Int, String]()
         for (i <- 1 to count) {
            m.put(i, s"$i")
          }
         m.toMap
     }
 }

为什么说Future未完成？

scala> getFutureMap(0).map { print}
Map()res6: scala.concurrent.Future[Unit] = Future(<not completed>)

Answer 1

当我尝试映射未来的响应时，我会在scala REPL 2.11.7中获取

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

scala> import scala.concurrent.ExecutionContext
import scala.concurrent.ExecutionContext

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

scala> getFutureMap(0).map { print}
Map()res7: scala.concurrent.Future[Unit] = scala.concurrent.impl.Promise$DefaultPromise@3f92a84e

scala> getFutureMap(100).map { print}
res8: scala.concurrent.Future[Unit] = scala.concurrent.impl.Promise$DefaultPromise@574cd322
Map(69 -> 69, 88 -> 88, 5 -> 5, 10 -> 10, 56 -> 56, 42 -> 42, 24 -> 24, 37 -> 37, 25 -> 25, 52 -> 52, 14 -> 14, 20 -> 20, 46 -> 46, 93 -> 93, 57 -> 57, 78 -> 78, 29 -> 29, 84 -> 84, 61 -> 61, 89 -> 89, 1 -> 1, 74 -> 74, 6 -> 6, 60 -> 60, 85 -> 85, 28 -> 28, 38 -> 38, 70 -> 70, 21 -> 21, 33 -> 33, 92 -> 92, 65 -> 65, 97 -> 97, 9 -> 9, 53 -> 53, 77 -> 77, 96 -> 96, 13 -> 13, 41 -> 41, 73 -> 73, 2 -> 2, 32 -> 32, 34 -> 34, 45 -> 45, 64 -> 64, 17 -> 17, 22 -> 22, 44 -> 44, 59 -> 59, 27 -> 27, 71 -> 71, 12 -> 12, 54 -> 54, 49 -> 49, 86 -> 86, 81 -> 81, 76 -> 76, 7 -> 7, 39 -> 39, 98 -> 98, 91 -> 91, 66 -> 66, 3 -> 3, 80 -> 80, 35 -> 35, 48 -> 48, 63 -> 63, 18 -> 18, 95 -> 95, 50 -> 50, 67 -> 67, 16 -> 16, 31 -> 31, 11 -> 11, 72 -> 72, 43 -> 43, 99 -> 99, 87 -> 87, 40 -> 40, 26 -> 26, 55 -> 55, 23 -> 23, 8 -> 8, 75 -> 75, 58 -> 58, 82 -> 82, 36 -> 36, 30 -> 30, 51 -> 51, 19 -> 19, 4 -> 4, 79 -> 79, 94 -> 94, 47 -> 47, 15 -> 15, 68 -> 68, 62 -> 62, 90 -> 90, 83 -> 83, 100 -> 100)

这里的关键是，在未来仍然保持异步时map /或foreach，您的代码执行会向前发展。

如果您想等到将来完成，请使用onComplete with partial function。

所以，在你的情况下，它将如下，

scala> import scala.util.Success
import scala.util.Success

scala> import scala.util.Failure
import scala.util.Failure

scala> getFutureMap(0).onComplete {
     | case Success(x) => println(x)
     |  case Failure(y) => println(y)
     | }
Map()

和，

scala>  getFutureMap(5).onComplete {
     |    case Success(x) => println(x)
     |    case Failure(y) => println(y)
     |  }
Map(5 -> 5, 1 -> 1, 2 -> 2, 3 -> 3, 4 -> 4)

斯卡拉期货：用空地图回归未来会使未来未完成

1 个答案: