How do I correctly use DI to inject a Play controller's constructor?

Question

I'm migrating a Play 2.3.x app to Play 2.5.x and am having some problems using dependency injection.

In 2.3 I had a trait HasRemoteActor which a controller would mix-in to have a reference to some remote actor based on configuration. Since this required the application's config object, it's now required that this becomes a class so the config can be injected. Here's my attempt:

/*
   Dummy controller that has environment and configuration manually injected.
*/
class ConfigurationController(env: play.api.Environment,
                              conf: play.api.Configuration) extends Controller {

}

/*
  Dummy controller that has environment and configuration manually injected, but 
  sets up a remote client.
*/ 
class RemoteActorController(env: play.api.Environment, conf: play.api.Configuration)
  extends ConfigurationController(env, conf) {

  protected val remoteActorName = "foo"
  private val remoteActorConf = conf.underlying.getConfig(remoteActorName)
  private val system = ActorSystem("HttpServerSystem", ConfigFactory.load())

  private val tcpInfo = remoteActorConf.getConfig("akka.remote.netty.tcp")
  private val hostname = tcpInfo.getString("hostname")
  private val port = tcpInfo.getString("port")

  val path = s"akka.tcp://PubSubMember@$hostname:$port/system/receptionist"

  private val initialContacts = Set(ActorPath.fromString(path))


  protected val client = system.actorOf(
    ClusterClient.props(ClusterClientSettings(system).withInitialContacts(
        initialContacts)),
    "ClusterClient"
  )
}

/*
   Actual controller whose actions correspond to endpoints in `conf/routes`.
*/
@Singleton
class BarController @Inject()(env: play.api.Environment,
                              conf: play.api.Configuration) extends
    RemoteActorController(env, conf) {

    // ...

}

However, when I start my application, I find that the actor system always fails to find to its port (even though nothing is listening on that port) irrespective of the port number.

play.api.UnexpectedException: Unexpected exception[ProvisionException: Unable to provision, see the following errors:

1) Error injecting constructor, org.jboss.netty.channel.ChannelException: Failed to bind to: /127.0.0.1:8888

There seems to be a problem with the timing of the injection, but I'm so new to DI that I'm having trouble debugging it.

I tried adding routesGenerator := InjectedRoutesGenerator to my build.sbt and prefixed my injected routes' associated controllers with @, but still find the same runtime exceptions.

Does anyone have suggestions?

"Failed to bind" often means that you already have an application using this port, try to change your configuration to use an other port. — vdebergue, Feb 14 '17 at 20:47
@vdebergue The ports aren't being used by either TCP or UDP. — erip, Feb 15 '17 at 00:59

score 1 · Accepted Answer · edited Feb 15 '17 at 14:28

1

I would not use inheritance for this. Instead, I would go for something like this (I'm going to assume you're using guice):

@Singleton
class RemoteActorAdapter @Inject() (env: Environment, conf: Configuration) {

  // all other initialization code
  val client: ActorRef = ???

}

In the controller that wants to use these things:

class MyController @Inject() (remoteAdapterProvider: Provider[RemoteActorAdapter]) extends Controller {
  def index = Action {
    remoteAdapterProvider.get.client ! Hello
  }
}

So the trick is that by using a provider, you're deferring the initialization of the binding etc. to the time until it is needed.

edited Feb 15 '17 at 14:28

erip

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answered Feb 14 '17 at 20:46

rethab

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While I like this approach more than the one I attempted, I still find that I'm getting bind errors. – erip Feb 15 '17 at 14:28
I think it's not binding the `RemoteActorAdapter` as a singleton... do you know how to bind this correctly in `Module.scala`? – erip Feb 15 '17 at 15:02
So the purpose of using a `Provider` was to defer the initialization. Does the initialization work the first time, but then fail, because it is not re-using the instance? Or does it also fail on the first attempt? In the former case, you may try something like this: `bind(classOf[RemoteActorAdapter]).to(classOf[RemoteActorAdapter]).in(new SingletonScope())`. In the latter case, I doubt this has anything to do with dependency injection. – rethab Feb 16 '17 at 06:19
I think I found the problem... it was totally disjoint from the DI. Rather, it was the `ConfigFactory.load()` call -- this was causing a problem and showing up as a bind error! – erip Feb 16 '17 at 12:32

How do I correctly use DI to inject a Play controller's constructor?

1 Answers1