If this is off-topic, my apologies, not sure where else to post it.
I'd like my commercial Java application to call a GPL application. Merely calling it is legal. However, I'd like to do more than that. I'd like to send information from my application to a (modified) GPL application in real time. How can I do it, legally?
For instance, what if I modify the GPL app to listen to a socket or standard input, can I then use it from my commercial app?
The modified GPL application will of course remain GPL; I just want to avoid having to GPL my entire work, simply because of this one little piece.