Client == server - problems with callbacks

Question

Hi everyone!
I'm having trouble establishing bidirectional communication between a client and a server (code samples are below).
Both classes (client & server) extend UnicastRemoteObject and implement Interfaces that are extending Remote. Now the client looks up the server and tries to register itself at the server by calling a method like this:
remote_server.setClient(this);
as long as I execute both programs in the same LAN this method-call works fine, but when client and server connect through internet I'm getting the following exception:
---------------------- Exception ------------------------>
java.rmi.ServerException: RemoteException occurred in server thread; nested exception is:
     java.rmi.ConnectException: Connection refused to host: 192.168.0.3; nested exception is:
     java.net.ConnectException: Connection timed out
     at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:292)
<---------------------- Exception ------------------------
maybe helpful:
- 192.168.0.3 is the client's LAN-IP
- I am directly connected to the internet via ADSL-modem (no router)
I searched the forums for several hours now, I read through the following tutorial,
http://developer.java.sun.com/developer/onlineTraining/rmi/exercises/RMICallback/index.html
but still I didn't find a solution.
I already spent a lot of time developing this and I start to get desperate, so I hope someone of you out there can help me!
pilord
==================== Codesamples =======================>
public class ServerImpl extends UnicastRemoteObject implements Server {
Client client;
public ServerImpl() {
LocateRegistry.getRegistry(1096).rebind("test",this);
/* specified in Remote-Interface: Server*/
public void setClient(Client client) {
this.client = client;
public class ClientImpl extends UnicastRemoteObject implements Client {
public ClientImpl() {
Server s = Naming.lookup("rmi://***.***.***.***:1096/test");
s.setClient(this); // HERE is the trouble.
<==================== Codesamples =======================

Answer 1

Don't feel lost, crumb. Http tunnelling is not as complex as it seems. I just started using RMI at my new job here and in a couple of weeks I've already picked up on alot of what I needed to know. (I just posted a question myself on the same topic.) Basically what you have to do is set up a web server for RMI to talk to at the server side. It will work if the webserver is listening on port 80 with the rmiservlet.ServletHandler registered to respond to any path request of cgi-bin/java-rmi.cgi. In other words "cgi-bin/java-rmi.cgi" should be the servlet-mapping of the ServletHandler. The servlet merly acts as a proxy on behalf of the RMI client and fowards the request to the desired port on the server. If you know how to set up a servlet as the default web app then it is really a breeze. On the client side you only need to set the http.proxyHost and http.proxyPort system properties to the appropriate values for your proxy server. (I mistyped these property names in my prior post use what I have here as I just read it out of the RMI book.) Do a search on HTTP tunnelling and you should turn up dozens of hits. I have the source to the servlet if you need it. I've already modified it for my own purposes though it should still work for you. If you forego http tunnelling then you'll have to do a complete app rewrite to use another protocol because RMI just doesn't work through firewalls without it. Alternatively you can get down and dirty with some low level sockets coding (this is what I'm thinking I'll end up doing eventually) to get it working without standard RMI/HTTP but that's way more complex. Unfortunately it looks like your callback code will need to be rewritten unless you either go commercial or do the socket stuff. (There does seem to be a shareware product called rmi doves that would help you here.) I'll be happy to assits you in any way as you need help.
Cliff