找不到隐式 ExecutionContext。你可能会通过spray scala
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Cannot find an implicit ExecutionContext. You might pass spray scala
提问by kam kimo
I have this two erros:
我有这两个错误：
Error:(39, 20) Cannot find an implicit ExecutionContext. You might pass
an (implicit ec: ExecutionContext) parameter to your method
or import scala.concurrent.ExecutionContext.Implicits.global.
val pipeline = sendReceive
^
Error:(39, 20) not enough arguments for method sendReceive: (implicit refFactory: akka.actor.ActorRefFactory, implicit executionContext: scala.concurrent.ExecutionContext, implicit futureTimeout: akka.util.Timeout)spray.client.pipelining.SendReceive.
Unspecified value parameter executionContext.
val pipeline = sendReceive
^
My Code is:
我的代码是：
import scala.util.{Success, Failure}
import scala.concurrent.duration._
import akka.actor.ActorSystem
import akka.pattern.ask
import akka.event.Logging
import akka.io.IO
import spray.can.Http
import spray.client.pipelining._
import spray.util._
import argonaut._, Argonaut._
object test {
case class Elevation(location: Location, elevation: Double)
case class Location(lat: Double, lng: Double)
case class GoogleApiResult(status: String, results: List[Elevation])
implicit def locationFormat: CodecJson[Location] = casecodec2(Location.apply, Location.unapply)("lat", "lng")
implicit def elevationFormat: CodecJson[Elevation] = casecodec2(Elevation.apply, Elevation.unapply)("location", "elevation")
implicit def googleApiResultFormat: CodecJson[GoogleApiResult] = casecodec2(GoogleApiResult.apply, GoogleApiResult.unapply)("status", "results")
object Main extends App {
// we need an ActorSystem to host our application in
implicit val system = ActorSystem("simple-spray-client")
// execution context for futures below
val log = Logging(system, getClass)
log.info("Requesting the elevation of Mt. Everest from Googles Elevation API...")
val pipeline = sendReceive
val responseFuture= pipeline {
Get("http://maps.googleapis.com/maps/api/elevation/json?locations=27.988056,86.925278&sensor=false")
}
responseFuture.onComplete {
case Success(result) =>
println(result)
log.info("The elevation of Mt.Everest is: {} m", result.toString.decodeOption[Elevation].get)
shutdown()
case Failure(error) =>
log.error(error, "Couldn't get elevation")
shutdown()
}
def shutdown(): Unit = {
IO(Http).ask(Http.CloseAll)(1.second).await
system.shutdown()
}
}
}`
回答by Fatih Donmez
You need to import scala.concurrent.ExecutionContext.Implicits.globalas error specify.
您需要import scala.concurrent.ExecutionContext.Implicits.global作为错误指定。
You see sendReceivemethod has implicit executionContext: scala.concurrent.ExecutionContextparameter.
你看到sendReceive方法有implicit executionContext: scala.concurrent.ExecutionContext参数。
--edit--
- 编辑 -
This answer is getting lots of view so I want to update it. As you see this is default global execution context, declared like;
这个答案得到了很多关注，所以我想更新它。如您所见，这是默认的全局执行上下文，声明如下；
/**
* The implicit global `ExecutionContext`. Import `global` when you want to provide the global
* `ExecutionContext` implicitly.
*
* The default `ExecutionContext` implementation is backed by a work-stealing thread pool. By default,
* the thread pool uses a target number of worker threads equal to the number of
* [[https://docs.oracle.com/javase/8/docs/api/java/lang/Runtime.html#availableProcessors-- available processors]].
*/
implicit lazy val global: ExecutionContextExecutor = impl.ExecutionContextImpl.fromExecutor(null: Executor)
It uses default work stealing pool. So you may need to provide different kind of execution context for different kind of concurrency need.
它使用默认的工作窃取池。因此，您可能需要为不同类型的并发需求提供不同类型的执行上下文。
