How to respond with the result of an actor call?

Question

We are looking at using Akka-HTTP Java API - using Routing DSL.

It's not clear how to use the Routing functionality to respond to an HttpRequest; using an Untyped Akka Actor. For example, upon matching a Route path, how do we hand off the request to a "handler" ActorRef, which will then respond with a HttpResponse in a asynchronous way?

A similar question was posted on Akka-User mailing list, but with no followup solutions as such - https://groups.google.com/d/msg/akka-user/qHe3Ko7EVvg/KC-aKz_o5aoJ.

Answer 1

This can be accomplished with a combination of the onComplete directive and the ask pattern.

In the below example the RequestHandlerActor actor is used to create a HttpResponse based on the HttpRequest. This Actor is asked from within the route.

I have never used Java for routing code so my response is in Scala.

import scala.concurrent.duration._
import akka.actor.ActorSystem
import akka.http.scaladsl.model.HttpResponse
import akka.http.scaladsl.model.HttpRequest
import akka.actor.Actor
import akka.http.scaladsl.server.Directives._
import akka.actor.Props
import akka.pattern.ask
import akka.util.Timeout
import scala.util.{Success, Failure}
import akka.http.scaladsl.model.StatusCodes.InternalServerError

class RequestHandlerActor extends Actor {
  override def receive = {
    case httpRequest : HttpRequest =>
      sender() ! HttpResponse(entity = "actor responds nicely")
  }
}

implicit val actorSystem = ActorSystem()
implicit val timeout = Timeout(5 seconds)

val requestRef = actorSystem actorOf Props[RequestHandlerActor]

val route = 
  extractRequest { request =>
    onComplete((requestRef ? request).mapTo[HttpResponse]) {
      case Success(response) => complete(response)
      case Failure(ex) => 
        complete((InternalServerError, s"Actor not playing nice: ${ex.getMessage}"))
    } 
  }

This route can then be used passed into the bindAndHandle method like any other Flow.