Play framework async I/O gotchas

PlayAsyncIOGotchas.java

public class AsyncTest extends Controller
{
  public static void gotchas()
  {
    params.put("foo", "bar");      // Check if changes to params survive the request being suspended
    renderArgs.put("foo", "bar");  // Check if changes to renderArgs survive the request being suspended
    final String foo = "bar";      // Must be declared final to use in the callback

    F.Promise<WS.HttpResponse> remoteCall1 = WS.url("http://www.remote-service.com/data/1").getAsync();
    F.Promise<WS.HttpResponse> remoteCall2 = WS.url("http://www.remote-service.com/data/2").getAsync();
    F.Promise<WS.HttpResponse> remoteCall3 = WS.url("http://www.remote-service.com/data/3").getAsync();
 
    F.Promise<List<WS.HttpResponse>> promises = F.Promise.waitAll(remoteCall1, remoteCall2, remoteCall3);

    await(promises, new F.Action<List<WS.HttpResponse>>()   // request gets suspended here
    {
      public void invoke(List<WS.HttpResponse> httpResponses)
      {
        System.out.println(params.get("foo"));      // prints "bar"
        System.out.println(renderArgs.get("foo"));  // prints null
        System.out.println(foo);                    // prints "bar"

        render(httpResponses);
      }
    });

    System.out.println("End");                      // never called
  }
}

See Play framework and async I/O for more information.