Play Framework 2.1 - Cannot find an implicit ExecutionContext

Question

I am calling a webservice like this:

WS
  .url(url)
  .get
  .map { response => // error occurs on this line
    response.status match {
      case 200 => Right(response.json)
      case status => Left(s"Problem accessing api, status '$status'")
  }
}

The complete error: Error: Cannot find an implicit ExecutionContext, either require one yourself or import ExecutionContext.Implicits.global

Broider

Answer 1

According to this issue, it is fixed in the documentation. I needed to add the following import:

import play.api.libs.concurrent.Execution.Implicits._

Broider

About the execution context. Some people think it's the same thing as the Scala global context. It however is not. Execution.scala is pointing to Invoker.scala So it actually is the execution context of the Play actor system. This allows you to change behavior using the application.conf – Broider

The "This issue" link is broken now. There is an archive on the web.archive though: web.archive.org/web/20140222113140/http://… – Washbasin

@Washbasin Thank you, I have adjusted the link – Broider

link broken again – Fettling

@Fettling Thanks for reporting. Too bad the internet does not have persistent links. – Broider

I'd say it's more correct to inject it from the injection framework as indicated below. particularly given that this is the way the example apps manage it. – Lex

Since play 2.6 you should use Guice dependency injection #14962208 – Allysonalma

Answer 2

Since Play 2.6 it's recommended to use guice dependency injection for execution context.

Default execution context injection:

Foo.scala

class Foo @Inject()()(implicit ec:ExecutionContext) {

def bar() = {
   WS.url(url)
     .get
     .map { response => // error occurs on this line
       response.status match {
         case 200 => Right(response.json)
         case status => Left(s"Problem accessing api, status '$status'")
     }
   }
}

Custom execution context injection:

application.conf

# db connections = ((physical_core_count * 2) + effective_spindle_count)
fixedConnectionPool = 9

database.dispatcher {
  executor = "thread-pool-executor"
  throughput = 1
  thread-pool-executor {
    fixed-pool-size = ${fixedConnectionPool}
  }
}

DatabaseExecutionContext.scala

@Singleton 
class DatabaseExecutionContext @Inject()(system: ActorSystem) extends CustomExecutionContext(system,"database.dispatcher")

Foo.scala

class Foo @Inject()(implicit executionContext: DatabaseExecutionContext ) {   ...    }

More info at:

https://www.playframework.com/documentation/2.6.x/Migration26#play.api.libs.concurrent.Execution-is-deprecated https://www.playframework.com/documentation/2.6.x/Highlights26#CustomExecutionContext-and-Thread-Pool-Sizing

Allysonalma

Your code does not inject the execution context. It still uses implicit resolution to get the execution context. – Broider

As per Play documentation (at least 2.6), @mgosk's answer is the standard; see: playframework.com/documentation/2.6.x/… – Glassman

There is, however, more to it. You can extend/define CustomExecutionContext too. See: playframework.com/documentation/2.6.x/… and playframework.com/documentation/2.6.x/… – Glassman