Scala syntactic sugar with java listener pattern

Question

I have to use java code in my scala project. The java code encourages the usage of a listener pattern. The code is something like this:

 asyncHttpClient.prepareGet("http://www.ning.com/ ").execute(new AsyncCompletionHandler<Response>(){

    @Override
    public Response onCompleted(Response response) throws Exception{
        // Do something with the Response
        // ...
        return response;
    }

    @Override
    public void onThrowable(Throwable t){
        // Something wrong happened.
    }
});

I am wondering if it is possible to use anything better in scala with this code. I know there is a paper written by Martin Odersky saying that observer pattern is bad but I didn't go deep with the matter. Thanks

Answer 1

If you can't change the signature of your execute method, you could write a convenience method to simplify creation of the callback:

def async(f: Response => Response)(handler: Throwable => Unit) =
   new AsyncCompletionHandler[Response]() {
      @throws(classOf[Exception])
      override def onCompleted(response: Response): Response = 
         f(response)

      override def onThrowable(t: Throwable) = handler(t)
   }

Then you can write your code like

 asyncHttpClient.prepareGet("http://www.ning.com/ ").execute(async {
    response => // do something with response
 } { 
    caught => // handle failure
 }