I have a single ipp printer on a Unix machine.
lpstat -v returns for me something like
device for printername: ipp://xx.xxx.xx.xx:631

Now, running several of the old image-printing 2D tests, I'm getting this exception:

 javax.print.PrintException: java.lang.ClassCastException: sun.print.IPPPrintService cannot be cast to sun.print.UnixPrintService
  at sun.print.UnixPrintJob.print(UnixPrintJob.java:418)
  at EventHandling.print(EventHandling.java:279)
  at EventHandling.start(EventHandling.java:168)
etc., because of the cast in line 413

Looking in the code, we see in UnixPrintJob.java at line 409:
                if (!(service instanceof IPPPrintService &&
                    ((IPPPrintService)service).isIPPSupportedImages(
                                                flavor.getMimeType()))) {
                    printableJob(new ImagePrinter(instream));
                    ((UnixPrintService)service).wakeNotifier();
                    return;
                }

Apparently, I have an IPP print service which doesn't support certain given mime type.