rmi - ConnectException

Question

This is my first time that I am using RMI, basically I manage to run the following RMI example locally on my PC but not via two separate Linux machines.

The server interface:

public interface PowerService extends Remote{
public BigInteger square ( int number )
    throws RemoteException;

public BigInteger power  ( int num1, int num2) 
    throws RemoteException;
}

The server:

public class PowerServiceServer extends UnicastRemoteObject implements
    PowerService {

public PowerServiceServer() throws RemoteException {
    super();
}

public BigInteger square(int number) throws RemoteException {
    imp .....
    return (bi);
}

public BigInteger power(int num1, int num2) throws RemoteException {
    imp .....
    return bi;
}

public static void main(String[] args) throws Exception {

    PowerServiceServer svr = new PowerServiceServer();
    // ... and bind it with the RMI Registry
    Naming.bind("PowerService", svr);
    System.out.println("Service bound....");
}
}

The client:

public class PowerServiceClient {
public static void main(String args[]) throws Exception {
    // Call registry for PowerService
    PowerService service = (PowerService) Naming.lookup("rmi://" + args[0]
            + "/PowerService");
    DataInputStream din = new DataInputStream(System.in);
    for (;;) {
        System.out.println("1 - Calculate square");
        System.out.println("2 - Calculate power");
        System.out.println("3 - Exit");
        System.out.println();
        System.out.print("Choice : ");

        String line = din.readLine();
        Integer choice = new Integer(line);

        int value = choice.intValue();

        switch (value) {
        case 1:
            // Call remote method
            ....................
            break;
        case 2:
            // Call remote method
            ....................
            break;
        case 3:
            System.exit(0);
        default:
            System.out.println("Invalid option");
            break;
        }
    }
}

and the client interfaces is the same like the server

This is what I did in order to run the rmi example:

1) On the server side I created the stub

2) Run rmiregisrty

3) Run the server

4) I copy the stub from the server side to the client side in to the same package

5) Run the client

After running the client I got the following error message:

Exception in thread "main" java.rmi.ConnectException: Connection refused to host: 127.0.0.1; nested exception is: java.net.ConnectException: Connection refused at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:601) at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:198) at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:184) at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:110) at compute.PowerServiceServer_Stub.square(Unknown Source)

is possible that due to some firewall I can’t connect or perhaps I am doing something wrong ??

Thanks

Is 127.0.0.1 the IP address you expected to be connecting to? In other words, is the client running on the same host as the server? NB your remote method implementations don't have to be declared as throwing RemoteException unless the compiler insist, which only happens if they call remote methods of their own, which is pretty uncommon. — user207421
no ip 127.0.0.1 is not the one i was expecting to see since the client is on a different machine (ip) — angus

user207421 user207421 · Accepted Answer · 2013-01-10T20:28:25

This is the problem addressed by java.rmi.server.hostname. See item A.1 in the RMI FAQ. You need to either fix the /etc/hosts misconfiguration that causes it, or set the system property java.rmi.server.hostname in the server JVM to the correct IP address of the server, before exporting any remote objects.

rmi - ConnectException

1 Answers