[akka-http] java completeWith mapping future

[Benoit Guillon]

Hi,

I'm using akka http with Java DSL and I'm trying to handle a get request with an actor and map my actor's response to the HTTP response as follows:

private Route getTasksRoute(){

   return path("tasks").route(pathEndOrSingleSlash().route(get(this.handleWith(

          (ctx) -> ctx.completeWith(handleGetTask(ctx))

   ))));

}

private Future<RouteResult> handleGetTask(RequestContext ctx){

   return Patterns.ask(actorSystem.actorFor("myActor"), buildMessage(), 1000)

       .map(o -> ctx.completeAs(Jackson.json(), o), ctx.executionContext());

}

This code does not compile in Java 8 because the API enforces to use scala futures

Error:(74, 17) java: method map in interface scala.concurrent.Future<T> cannot be applied to given types;

  required: scala.Function1<java.lang.Object,S>,scala.concurrent.ExecutionContext

  found: (o)->ctx.c[...]), o),scala.concurrent.ExecutionContext

  reason: cannot infer type-variable(s) S

    (argument mismatch; scala.Function1 is not a functional interface

      multiple non-overriding abstract methods found in interface scala.Function1)

I could not find any relevant code example illustrating this use case in java.

Can you suggest a code pattern to illustrate how the completeWith method is intended to be used in Java 8 in conjonction with actors' ask pattern ?

Thanks for your help.

Benoit

[André]

Hi Benoit,

you should take a look at http://doc.akka.io/docs/akka/snapshot/java/futures.html#Future_is_a_Monad.

Mapper should solve your Problem.

Cheers

André

[Benoit Guillon]

Hi André,

Thanks for your reply, using Mapper works fine (a bit more verbose than the scala implementation)

For those who have the same issue: here is the solution:

private Future<RouteResult> handleGetTask(RequestContext ctx){

    return Patterns.ask(actorSystem.actorFor("myActor"), buildMessage(), 1000)

            .map(new Mapper<Object, RouteResult>(){

                public RouteResult apply(Object o) {

                    return ctx.completeAs(Jackson.json(), o);

                }

          }, ctx.executionContext());

}

Thanks

Benoit

[Patrik Nordwall]

The Scala Future API is rather clunky for Java when you get used to Java8 lambas. You can try the scala-java8-compat library and work with CompletionStage instead.

Cheers,

Patrik

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[Erik Frister]

Thanks Benoit for posting the explicit solution, that saved my some headaches!

For anyone having similar issues like me: be aware that you need to import the scala Future for the return type of the "handleGetTask" method, not the Java future! Otherwise you'll get compilation errors regarding incorrect mapping of types.

import scala.concurrent.Future;

Furthermore, André's code can be slightly simplified by using "handleWithAsync" and Java 8 method references. Instead of:

private Route getTasksRoute(){

   return path("tasks").route(pathEndOrSingleSlash().route(get(this.handleWith(

          (ctx) -> ctx.completeWith(handleGetTask(ctx))

   ))));

}

You can just write:

private Route getTasksRoute(){

   return path("tasks").route(pathEndOrSingleSlash().route(get(handleWithAsync(

          this::handleGetTask

   ))));

}

Hope that helps anyone.

Cheers

Erik