如何确定当前正在使用的远程RMI服务器端口

Question

I have a java process running (on java 7) on some remote server that I want to monitor using Java Mission Control. However, JMC is unable to connect, although I can telnet to the server using the port jmx remote port (12345 here, see below).

The remote java proces is started with

-Dcom.sun.management.jmxremote=true 
-Dcom.sun.management.jmxremote.ssl=false 
-Dcom.sun.management.jmxremote.port=12345 
-Djava.rmi.server.hostname=<some ip address>
-Dcom.sun.management.jmxremote.authenticate=false

and these seem to be correct values to me. Port 12345 has been opened on the firewall, but I suspect that the rmi server port is blocked by the firewall.

Thus, my question is: Is there any way (using netstat on the server or maybe even telnet from the client) to determine which rmi server port the java process is currently using on the server? (Using netstat, I see several ports being used by the java process. However, I don't have a clue which one is the rmi port.)

Answer 1

This should display where a JMX remote client is told to connect to (plus some internal info) possibly after timing out:

//nopackage -- move if you like
import java.rmi.Remote;
import java.rmi.registry.*;
import java.rmi.server.*;
import sun.rmi.server.UnicastRef;
import sun.rmi.transport.LiveRef;

public class JMXTarget {
    /*
     * run: java JMXTarget host port
     * where host (name or address) contains the JVM process offering JMX
     * and port (number) is the registry specified by -Dcom.sun.management.jmxremote.port 
     */
    public static void main(String[] args) throws Exception {
        Registry reg = LocateRegistry.getRegistry (args[0], Integer.parseInt(args[1]));
        Remote r = reg.lookup ("jmxrmi");
        RemoteObject ro = (RemoteObject)r; 
        RemoteRef rr = ro.getRef();
        UnicastRef ur = (UnicastRef)rr;
        LiveRef lr = ur.getLiveRef();
        System.out.println (lr);
    }
}

Note if sysprop java.rmi.server.hostname is specified as you did, its value (your "some ip address") is where the client connects. If that value is not an address of the target machine, or a name that resolves (for the client) to an address of the target machine, it won't connect. If you don't specify it, it defaults to (edit) the value determined by InetAddress.getLocalHost() which is or at least should be a valid address for that machine.

Answer 2

Adding '-Dcom.sun.management.jmxremote.rmi.port=12345' could help

See Why Java opens 3 ports when JMX is configured?