Use Akka Streams instead of Akka Actors

[wsargent]

This PR moves the reactive stocks example to use streams instead of actors as the underlying mechanic. The underlying code is the same as the Scala version, only with some tweaks necessitated by Jackson's serialization.

One thing that was surprising is that the websocket client ignores the value set for "Origin" and instead sends the same value as serverURL. It fails because it's on a different port rather than because it's checking the header and finding a difference.

Fixes #46

Supersedes #51

Compare with playframework/play-scala-websocket-example#74 (scala version of websocket example)

[richdougherty]

It looks good to me, but you might also want to get a review from someone who knows this app and streams a bit better. :)

[richdougherty]

Delete this?

[wsargent]

Done. BTW, I lost the ability to merge PRs on the examples somewhere down the line (github status altered?)

[richdougherty]

I'll check up on your Github status for the examples. If you like you can email me if there's anything you think you should have access to that you don't and I'll sort it out. :)

[richdougherty]

@wsargent, I've now given you (and the rest of the Core team in Github) Write access to all example repos. Let me know how you get on next time you try to merge.

[marcospereira]

Will, I'm getting the following error if I close the browser tab:

[error] a.a.RepointableActorRef - Error in stage [akka.stream.scaladsl.MergeHub$$anon$2@164b5b45]: Upstream producer failed with exception, removing from MergeHub now
akka.stream.scaladsl.MergeHub$ProducerFailed: Upstream producer failed with exception, removing from MergeHub now
	at akka.stream.scaladsl.MergeHub$$anon$2$$anon$4.onUpstreamFailure(Hub.scala:261)
	at akka.stream.impl.fusing.GraphInterpreter.processEvent(GraphInterpreter.scala:485)
	at akka.stream.impl.fusing.GraphInterpreter.execute(GraphInterpreter.scala:368)
	at akka.stream.impl.fusing.GraphInterpreterShell.runBatch(ActorGraphInterpreter.scala:571)
	at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:457)
	at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:546)
	at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:725)
	at akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:740)
	at akka.actor.Actor.aroundReceive(Actor.scala:513)
	at akka.actor.Actor.aroundReceive$(Actor.scala:511)
Caused by: java.util.concurrent.TimeoutException: No demand signalled in the last 1 second.
	at akka.stream.impl.Timers$BackpressureTimeout$$anon$4.onTimer(Timers.scala:133)
	at akka.stream.stage.TimerGraphStageLogic.onInternalTimer(GraphStage.scala:1228)
	at akka.stream.stage.TimerGraphStageLogic.$anonfun$getTimerAsyncCallback$1(GraphStage.scala:1217)
	at akka.stream.stage.TimerGraphStageLogic.$anonfun$getTimerAsyncCallback$1$adapted(GraphStage.scala:1217)
	at akka.stream.impl.fusing.GraphInterpreter.runAsyncInput(GraphInterpreter.scala:443)
	at akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:453)
	at akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:546)
	at akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:725)
	at akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:740)
	at akka.actor.Actor.aroundReceive(Actor.scala:513)

We should "fail" more gracefully here, I think.

[wsargent]

From

at akka.stream.impl.Timers$BackpressureTimeout$$anon$4.onTimer(Timers.scala:133)

that is the backpressure timeout -- I removed it.