RMI Example – Message, illustrates retrieving a message from an object located on a remote server. Requires the following classes

Rem.java  Establishes which methods the client can access in the remote object. 





import java.rmi.*;

/** The RMI client will use this interface directly. The RMI
 *  server will make a real remote object that implements this,
 *  then register an instance of it with some URL.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public interface Rem extends Remote {
  public String getMessage() throws RemoteException;
}


RemClient.java  The client application which communicates to the remote object and retrieves the message. 

import java.rmi.*; // For Naming, RemoteException, etc.
import java.net.*; // For MalformedURLException
import java.io.*;  // For Serializable interface

/** Get a Rem object from the specified remote host.
 *  Use its methods as though it were a local object.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemClient {
  public static void main(String[] args) {
    try {
      String host =
        (args.length > 0) ? args[0] : "localhost";
      // Get the remote object and store it in remObject:
      Rem remObject =
        (Rem)Naming.lookup("rmi://" + host + "/Rem");
      // Call methods in remObject:
      System.out.println(remObject.getMessage());
    } catch(RemoteException re) {
      System.out.println("RemoteException: " + re);
    } catch(NotBoundException nbe) {
      System.out.println("NotBoundException: " + nbe);
    } catch(MalformedURLException mfe) {
      System.out.println("MalformedURLException: " + mfe);
    }
  }
}


RemImpl.java  The concrete, remote object that implements the methods in Rem.java. 

import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

/** This is the actual implementation of Rem that the RMI
 *  server uses. The server builds an instance of this, then
 *  registers it with a URL. The client accesses the URL and
 *  binds the result to a Rem (not a RemImpl; it doesn't
 *  have this).
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemImpl extends UnicastRemoteObject
                     implements Rem {
  public RemImpl() throws RemoteException {}

  public String getMessage() throws RemoteException {
    return("Here is a remote message.");
  }
}


RemServer.java  Creates an instance of RemImpl on the remote server and binds the object in the registry for lookup by the client. 

import java.rmi.*;
import java.net.*;

/** The server creates a RemImpl (which implements the Rem
 *  interface), then registers it with the URL Rem, where
 *  clients can access it.
 *
 *  Taken from Core Web Programming from
 *  Prentice Hall and Sun Microsystems Press,
 *  .
 *  © 2001 Marty Hall and Larry Brown;
 *  may be freely used or adapted.
 */

public class RemServer {
  public static void main(String[] args) {
    try {
      RemImpl localObject = new RemImpl();
      Naming.rebind("rmi:///Rem", localObject);
    } catch(RemoteException re) {
      System.out.println("RemoteException: " + re);
    } catch(MalformedURLException mfe) {
      System.out.println("MalformedURLException: " + mfe);
    }
  }
}