How to send a message from Java to Erlang?

I'm making a application in Erlang, with a GUI in Java. I've managed to establish a connection between the to languages, but now i need to (i guess) send a message from Java to Erlang, every time I e.g press a button.

Is that the right way to go?

How would such a message look?

I've found a few good sites about this form of integration, but I feel like im not getting everything.

http://www.trapexit.org/How_to_communicate_java_and_erlang

If jinterface is too complicated you might just use the packet option on open_port and use

byte[] in_buf = new byte[256];
byte[] out_buf = new byte[256];
int in_count = System.in.read ();
int offset = 0; 
do
    {
        int c = System.in.read (in_buf, offset, in_count-offset);
        offset += c;
    }
while (offset < in_count);

To read packets from erlang and to write use:

System.out.write(out_count);
System.out.write(out_buf, 0, out_count);

On the erlang side this would match with

open_port({spawn, "<path-to-java> -cp <classpath> your-java-prog", 
          [{packet, 1}]).

If you need larger packets use {packet, 2} or {packet, 4} and adapt the java. Inside the packets you can run whatever protocol you like on both sides.