Question

Supposed I need to return a promise from my method, that depends on an external resource and some calculation. What I imagine is something like:

Promise<Integer> foo() {
  return WS.url(url)
    .getAsync()
    .callWhenReady(new Function<HttpResponse>(){
      Integer parse(HttpResponse response) {
        // parsing business logic 
        // ...
        int parsed = ...;
        return parsed;
      }
  });
} 

What can I use for callWhenReady? This is essentially just like jQuery.promise() behaves.

Answer 1

I think you want F.Promise.map (Play 2.0.2):

    /**
     * Maps this promise to a promise of type <code>B</code>.  The function <code>function</code> is applied as
     * soon as the promise is redeemed.
     *
     * Exceptions thrown by <code>function</code> will be wrapped in {@link java.lang.RuntimeException}, unless
     * they are <code>RuntimeException</code>'s themselves.
     *
     * @param function The function to map <code>A</code> to <code>B</code>.
     * @return A wrapped promise that maps the type from <code>A</code> to <code>B</code>.
     */
    public <B> Promise<B> map(final Function<A, B> function) {
        return new Promise<B>(
            promise.map(new scala.runtime.AbstractFunction1<A,B>() {
                public B apply(A a) {
                    try {
                        return function.apply(a);
                    } catch (RuntimeException e) {
                        throw e;
                    } catch(Throwable t) {
                        throw new RuntimeException(t);
                    }
                }
            })
        );
    }

It seems from your code that you’re using an earlier version Play, but I think you should still just be able to replace callWhenReady with map (and add an Integer type parameter to your callback function).