Akka Remote: get autogenerated port - akka

Question

I have a Java client, which obtains an autogenerated port. After starting the actor system, I want to access the port.
Config clientConfig = ConfigFactory.parseString("akka.remote.netty.tcp.port = 0")
.withFallback(ConfigFactory.parseString("akka.remote.netty.tcp.hostname = " + serverHostName))
.withFallback(ConfigFactory.load("common"));
actorSystem = ActorSystem.create("clientActorSystem", clientConfig);
// how to access the generated port here..!?
The port must already be set since the log output after ActorSystem.create(...) is like that:
[INFO] [03/31/2016 14:11:32.042] [main] [akka.remote.Remoting] Starting remoting
[INFO] [03/31/2016 14:11:32.233] [main] [akka.remote.Remoting] Remoting started; listening on addresses :[akka.tcp://actorSystem#localhost:58735]
[INFO] [03/31/2016 14:11:32.234] [main] [akka.remote.Remoting] Remoting now listens on addresses: [akka.tcp://actorSystem#localhost:58735]
If I try to get it via the configuration with actorSystem.settings().config().getValue("akka.remote.netty.tcp.port"), I still get 0 as defined before.
Has anyone an idea how this port (58735 in the example) can be accessed?

Answer 1

Using scala you can get Option of port on which Actor system is currently running:
val port = system.provider.getDefaultAddress.port
Hope you will be able to get the same code in Java.

Answer 2

The accepted answer probably worked for older versions of Akka but as of now (version 2.5.x) you will be getting something like:
Error:(22, 18) method provider in trait ActorRefFactory cannot be accessed in akka.actor.ActorSystem
The solution would be to use akka extensions. Here is how I use it:
Example. scala
package example
import akka.actor._
class AddressExtension(system: ExtendedActorSystem) extends Extension {
val address: Address = system.provider.getDefaultAddress
}
object AddressExtension extends ExtensionId[AddressExtension] {
def createExtension(system: ExtendedActorSystem): AddressExtension = new AddressExtension(system)
def hostOf(system: ActorSystem): String = AddressExtension(system).address.host.getOrElse("")
def portOf(system: ActorSystem): Int = AddressExtension(system).address.port.getOrElse(0)
}
object Main extends App {
val system = ActorSystem("Main")
println(AddressExtension.portOf(system))
}