RMI Registry and UnicastRemoteOb jects - sharing ports

[Alexandr Molochnikov]

Hello group,

I am trying to cut down the number of ports that must be opened in a
firewall to let the client talk to the protected server. The server runs its
own registry process by calling LocateRegistry. createRegistry( port), and the
same port is used when UnicastRemoteOb jects are exported. This way, I can
tell the firewall admin to open only one hole in the firewall, instead of
two.

It all works, until I attempt to use a custom socket factory for the
registry (the factory explicitly sets the IP address to which the registry
binds - important for the multi-homed servers). If I set the socket factory
to the registry only:

LocateRegistry. createRegistry( port, null, mySocketFactory )

and leave the exported objects to their default factory settings, I get a
"port already in use" exception. If I set the same instance of the socket
factory to the UnicastRemoteOb jects, this is what happens:

1. The first UnicastRemoteOb jects exports normally and responds to the
remote calls.
2. Any other UnicastRemoteOb ject to be exported on the same port with the
same instance of the socket factory throws the same old "port already in
use" exception.

What am I missing in my version of the socket factory that the default
implementation has and what lets it bind multiple objects to the same port
without blowing up?

Here is the source code for the socket factory:

public class RegistrySocketF actory extends RMISocketFactor y implements
Serializable
{
private InetAddress ipInterface = null;
private static RegistrySocketF actory instance = null; // turn this
class into a singleton
public RegistrySocketF actory(InetAddr ess ipInterface)
{
this.ipInterfac e = ipInterface;
instance = this;
}
public static RegistrySocketF actory getInstance()
{
return (instance);
}
public ServerSocket createServerSoc ket(int port)
{
ServerSocket serverSocket = null;
try
{
serverSocket = new ServerSocket(po rt, 50, ipInterface);
}
catch (Exception e)
{
System.out.prin tln(e);
}
return (serverSocket);
}
public Socket createSocket(St ring ipInterface, int port) throws
IOException
{
Socket socket= new Socket(ipInterf ace, port);
return socket;
}
}

And this is the snippet of the context in which it is used:

RegistrySocketF actory socketFactory = new RegistrySocketF actory(address) ;
LocateRegistry. createRegistry( 6541, null, socketFactory);
proxy = new Proxy(6541); // this works
proxyHook = new ProxyHook(this) ; // this throws "port in use"
exception

public Proxy(int port) throws RemoteException
{
super(6541, null, RegistrySocketF actory.getInsta nce());
}

public ProxyHook(Proxy controller) throws RemoteException
{
super(6541, null, RegistrySocketF actory.getInsta nce());
}