RMI CallBack

import java.rmi.*; import java.rmi.server.*; import java.util.Vector; /** * This class implements the remote interface * CallbackServerInterface. * @author M. L. Liu */ public class CallbackServerImpl extends UnicastRemoteObject implements CallbackServerInterface { private Vector clientList; public CallbackServerImpl() throws RemoteException { super( ); clientList = new Vector(); } public String sayHello( ) throws java.rmi.RemoteException { return("hello"); } public synchronized void registerForCallback( CallbackClientInterface callbackClientObject) throws java.rmi.RemoteException{ // store the callback object into the vector if (!(clientList.contains(callbackClientObject))) { clientList.addElement(callbackClientObject); System.out.println("Registered new client "); doCallbacks(); } // end if } // This remote method allows an object client to // cancel its registration for callback // @param id is an ID for the client; to be used by // the server to uniquely identify the registered client. public synchronized void unregisterForCallback( CallbackClientInterface callbackClientObject) throws java.rmi.RemoteException{ if (clientList.removeElement(callbackClientObject)) { System.out.println("Unregistered client "); } else { System.out.println( "unregister: clientwasn't registered."); } } private synchronized void doCallbacks( ) throws java.rmi.RemoteException{ // make callback to each registered client System.out.println( "**************************************\n" + "Callbacks initiated ---"); for (int i = 0; i < clientList.size(); i++){ System.out.println("doing "+ i +"-th callback\n"); // convert the vector object to a callback object CallbackClientInterface nextClient = (CallbackClientInterface)clientList.elementAt(i); // invoke the callback method nextClient.notifyMe("Number of registered clients=" + clientList.size()); }// end for System.out.println("********************************\n" + "Server completed callbacks ---"); } // doCallbacks }// end CallbackServerImpl class