How to send a message from Java to Erlang?

Question

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

Answer 1

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.

Answer 2

Besides classic Java-Erlang communication via OTP jinterface you can research such methods like:

 - thrift
 - ice from zeroC (no official erlang binding)
 - maybe two http servers on both sides (I like this approach) 
 - protocol buffers (rather not, it is better for larger data transfers)

You need to learn the shape of your traffic and choose the best solution. Jinterface is not so bad, tho.. (here is official doc: http://www.erlang.org/doc/apps/jinterface/jinterface_users_guide.html)

Answer 3

I am working on an application similar to yours: C++ GUI and Erlang server. I use TCP sockets to exchange messages between the GUI and server, and Erlang server patterns for handling requests (I may have more than one GUI hooked up to the server at the same time).