Re: RMI & connection refused

Nigel Wade <>
Mon, 03 Aug 2009 16:25:58 +0100
Matt Humphrey wrote:

"Nigel Wade" <> wrote in message

That is one of the joys of this type of networking. Usually you have to
open all
high ports (1024 up) incoming from the client. I imagine that RMI has any
in way of opening ports (it would hardly be portable, and Java should be
portable). Offhand I can't remember whether RMI allows a server to listen
on a
specific port and then register that port with rmiregistry. If it did at
you'd only have to open one port.

You can use RMI without a registry and declare the port your service is
accessed on and you can open just that one in your firewall.

Ok, I wasn't aware of that. I've only used RMI with the rmiregisty to handle
port numbers for the client. I generally only use RMI on the one host
(client=server=registry), and only have ports open to my development machine
and blocked to all other systems. I couldn't see anything in the RMI API which
allowed you to specify the RMI server port number.

If your server
happens to create additional remote objects, each will get its own port. You
don't have to know or handle the port number, but a firewall will block
access. Similarly, remote objects instantiated on the client (RMI
callbacks) will open a server socket on the client and the server's remote
proxy will attempt to connect to that port. Again, you don't have to know
any of the port numbers for this to work, I'd rather not open ports on the

If you don't use the rmiregistry, and you don't know or handle the port numbers,
how does the client determine the port number on which the server is listening?

Nigel Wade

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