There are two ways to connect to your Erlang code through Jinterface: messages and RPC.
RPC is documented here: http://www.erlang.org/doc/apps/jinterface/jinterface_users_guide.html#id57655
Note that it is not "non-OTP" to use messages. If you've got a gen_server, you can message it directly and receive the message in the handle_info function.