1026: Mainline

Clients and servers communicate with each other via a registry running on the server computer.

The registry needs to be informed about instance that are to be accessed by clients. Thus, to create a RatingServer instance that is ready to receive method calls from a client computer, you must establish a connection with the server computer's running registry program.

The connection is done via a class method, rebind, of the Naming class, which connects a name with a remotely accessible instance. The rebind method takes two arguments: one is a host identifier, combined with a name of your choice. The second is the remotely accessible instance.

The host identifier is a specification, such as whitney.ai.mit.edu, that specifies the computer on which the registry runs. Typically, this computer is the same one on which the server runs, in which case the host identifier is localhost. The client uses a name of your choice—such as ratingService—to tell the registry what the client seeks.

Because both rebind and the RatingServer constructor throw exceptions, both the rebind call and the RatingServer construction must appear in a try–catch combination.

import java.rmi.*;
import java.rmi.server.*;
public class RatingServer extends UnicastRemoteObject
                          implements RatingServerInterface {
 public RatingServer () throws RemoteException {
  super();
 }
 public int serverRating (MovieInterface m) throws RemoteException {
  System.out.println("RatingServer asked for a rating");
  int s = m.getScript();
  int a = m.getActing();
  int d = m.getDirection();
  return 3 * Math.max(Math.max(s, a), d);
 }
 public static void main(String[] args) {
  try {
   Naming.rebind("//localhost/ratingService", new RatingServer()); 
   System.out.println("Rating server connected to server"); 
  } 
  catch (Exception e) { 
   System.err.println("RatingServer exception: " + e.getMessage()); 
   e.printStackTrace();  
  } 
 } 
}