I am creating my first, very simple RMI client-server application.
Here is the code:
Interface "ICommunication"
package itu.exercies.RMI.server;
import java.rmi.Remote;
import java.rmi.RemoteException;
public interface ICommunication extends Remote
{
public String doCommunicate(String name) throws RemoteException;
}
Interface implementation "CommunicationImpl":
package itu.exercies.RMI.server;
import java.rmi.RemoteException;
import java.rmi.server.UnicastRemoteObject;
public class CommunicationImpl extends UnicastRemoteObject implements ICommunication {
/**
*
*/
private static final long serialVersionUID = 1L;
public CommunicationImpl() throws RemoteException {
super();
}
@Override
public String doCommunicate(String name) throws RemoteException {
return "Hello this is server , whats up " +name+ " ?!\n";
}
}
Here is my main class of the server "CommunicationServer":
package itu.exercies.RMI.server;
import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.RemoteException;
public class CommunicationServer {
/**
* @param args
* @throws RemoteException
* @throws MalformedURLException
*/
public static void main(String[] args) throws RemoteException, MalformedURLException {
CommunicationImpl imp = new CommunicationImpl();
Naming.rebind("CommunicationImpl", imp);
System.out.println("Server started...");
System.out.println("Object successfully registered. It is bound to the name 'CommunicationImpl'.");
}
}
And this is my client "CommunicationClient":
package itu.exercies.RMI.client;
import java.net.MalformedURLException;
import java.rmi.Naming;
import java.rmi.NotBoundException;
import java.rmi.RemoteException;
import itu.exercies.RMI.server.CommunicationImpl;
public class CommunicationClient {
public static void main(String[] args) throws MalformedURLException, RemoteException, NotBoundException {
String url = new String("rmi://localhost/CommunicationImpl");
CommunicationImpl comm = (CommunicationImpl)Naming.lookup(url);
String reply = comm.doCommunicate("Wiktor");
System.out.println(reply);
}
}
Now when I try to run it:
java itu.exercies.RMI.client.CommunicationClientException in thread "main" java.lang.ClassCastException: $Proxy0 cannot be cast to itu.exercies.RMI.server.CommunicationImpl at itu.exercies.RMI.client.CommunicationClient.main(CommunicationClient.java:14)
So far I have tried to fix it by creating a stub of 'CommunicationImpl' object using rmic but now instead of '$Proxy0' the error refers to 'CommunicationImpl_Stub':
Exception in thread "main" java.lang.ClassCastException: itu.exercies.RMI.server.CommunicationImpl_Stub cannot be cast to itu.exercies.RMI.server.CommunicationImpl at itu.exercies.RMI.client.CommunicationClient.main(CommunicationClient.java:14)
At this point I have no idea were to look for errors. Can anybody give me any suggestions?
Replace
CommunicationImpl comm = (CommunicationImpl) Naming.lookup(url);
with
ICommunication comm = (ICommunication) Naming.lookup(url);
CommunicationImpl
is the server implementation of the ICommunication
. The client neither knows nor cares about the implementation, only the interface.
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