我正在尝试进行大量外部服务调用,每个调用都跟进异常处理和有条件的进一步处理。我认为在内部使用 .onComplete 来扩展这个不错的 ( Asynchronous IO in Scala with futures ) 示例会很容易,但似乎我对范围界定和/或 Futures 不了解。谁能指出我正确的方向?
#!/bin/bash
scala -feature $0 $@
exit
!#
import scala.concurrent.{future, blocking, Future, Await}
import scala.concurrent.ExecutionContext.Implicits.global
import scala.concurrent.duration._
import scala.util.{Success, Failure}
import scala.language.postfixOps
val keylist = List("key1", "key2")
val myFuts: List[Future[String]] = keylist.map {
myid => future {
// this line simulates an external call which returns a future (retrieval from S3)
val myfut = future { Thread.sleep(1); "START " + myid}
var mystr = "This should have been overwritten"
myfut.onComplete {
case Failure(ex) => {
println (s"failed with error: $ex")
mystr = "FAILED"
}
case Success(myval) => {
mystr = s"SUCCESS $myid: $myval"
println (mystr)
}
}
mystr
}
}
val futset: Future[List[String]] = Future.sequence(myFuts)
println (Await.result(futset, 10 seconds))
在我的电脑(Scala 2.10.4)上,打印出:
SUCCESS key2: START key2
SUCCESS key1: START key1
List(This should have been overwritten, This should have been overwritten)
我想要(顺序不重要):
SUCCESS key2: START key2
SUCCESS key1: START key1
List(SUCCESS key2: START key2, SUCCESS key1: START key1)
最佳答案
我会避免使用 onComplete
并尝试使用它对可变变量执行副作用逻辑。相反,我会映射 future 并将失败案例处理为返回不同的值。这是您的代码的一个稍微修改的版本,在 Future
上使用 map
(通过 for comprehension),然后使用 recover
来处理失败情况.希望这就是您要找的:
val keylist = List("key1", "key2")
val myFuts: List[Future[String]] = keylist.map {myid =>
// this line simulates an external call which returns a future (retrieval from S3)
val myfut = future { Thread.sleep(1); "START " + myid}
val result = for (myval <- myfut) yield {
val res = s"SUCCESS $myid: $myval"
println(res)
res
}
result.recover{
case ex =>
println (s"failed with error: $ex")
"FAILED"
}
}
val futset: Future[List[String]] = Future.sequence(myFuts)
println (Await.result(futset, 10 seconds))
关于scala - 使用带有 onComplete 的 Scala future 列表进行异步处理以进行异常处理,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/23358204/