Consuming a service using WS in Play - scala

Question

I was hoping someone can briefly go over the various ways of consuming a service (this one just returns a string, normally it would be JSON but I just want to understand the concepts here).
My service:
def ping = Action {
Ok("pong")
}
Now in my Play (2.3.x) application, I want to call my client and display the response.
When working with Futures, I want to display the value.
I am a bit confused, what are all the ways I could call this method i.e. there are some ways I see that use Success/Failure,
val futureResponse: Future[String] = WS.url(url + "/ping").get().map { response =>
response.body
}
var resp = ""
futureResponse.onComplete {
case Success(str) => {
Logger.trace(s"future success $str")
resp = str
}
case Failure(ex) => {
Logger.trace(s"future failed")
resp = ex.toString
}
}
Ok(resp)
I can see the trace in STDOUT for success/failure, but my controller action just returns "" to my browser.
I understand that this is because it returns a FUTURE and my action finishes before the future returns.
How can I force it to wait?
What options do I have with error handling?

Answer 1

If you really want to block until feature is completed look at the Future.ready() and Future.result() methods. But you shouldn't.
The point about Future is that you can tell it how to use the result once it arrived, and then go on, no blocks required.
Future can be the result of an Action, in this case framework takes care of it:
def index = Action.async {
WS.url(url + "/ping").get()
.map(response => Ok("Got result: " + response.body))
}
Look at the documentation, it describes the topic very well.
As for the error-handling, you can use Future.recover() method. You should tell it what to return in case of error and it gives you new Future that you should return from your action.
def index = Action.async {
WS.url(url + "/ping").get()
.map(response => Ok("Got result: " + response.body))
.recover{ case e: Exception => InternalServerError(e.getMessage) }
}
So the basic way you consume service is to get result Future, transform it in the way you want by using monadic methods(the methods that return new transformed Future, like map, recover, etc..) and return it as a result of an Action.
You may want to look at Play 2.2 -Scala - How to chain Futures in Controller Action and Dealing with failed futures questions.