Java – “when creating a simple RMI application,” ClassCastException: $proxy0 cannot be converted “error

I am creating my first very simple RMI client - server application

This is the code:

Interface "communication"

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";
    }

}

This is my main server class "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'.");

    }

}

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 I try to run it:

>I use the terminal to navigate to the bin directory of my project. From there, I run rmiresistry > I run my communicationserver from a new terminal window (it prints out messages to make it seem to work) > I open the third terminal window. When I try to run my communicationclient, it throws an exception

So far, I've tried to fix it by using RMIC to create a stub of a "communicationimpl" object, but now instead of '$proxy0', the error refers to 'communicationimpl'_ Stub’：

At this point, I don't know what to look for Can anyone give me any advice?

Solution

replace

CommunicationImpl comm = (CommunicationImpl) Naming.lookup(url);

with

ICommunication comm = (ICommunication) Naming.lookup(url);

Communicationimpl is the server implementation of icommunication The client neither knows nor cares about the implementation, only the interface