public int port() {
        if (!serverChannel.isOpen()) {
            return -1;
        }
        return serverChannel.socket().getLocalPort();
    }
Obtain the local port number this Acceptor is listening to. If
this Acceptor is no longer listening (it has been shut down),
-1 will be returned.

@return listening port, or -1 if not listening
jrt/src/com/yahoo/jrt/Acceptor.java