Java midi api: direct connection between external midi devices

I'm trying to connect two external MIDI devices to each other, in order to press a button on one piano and play a sound on the other one. So far I'm able to receive midi data and sending it to my own receiver which basically just prints out the received information into the console, and I'm able to send a sequence to my external synth. But I can't seem to connect both. Is there someone that has done something similar and maybe can point me to a piece of code that could help me? Thanks, FlyingV