Trying to realize mandatory field validation on my form (outside fileUpload component), when upload button is pressed.

Since "validator" does not work yet, I use "onupload" event to intercept. Here I can do my validation and I am able to throw FacesMessage on error.

But:

The Message ist just shown shortly, then disappears and die upload is not cancelled.

Hence, the only way I see to interrupt is, throwing an exception. But throwing an exception at this time appears to be a kind of "global killer" for my whole application.

Is there any other way to tell fileUpload component not to start upload and keep FacesMessage displayed?