rmi callback

[simranjit singh]

my client is able to use functions stored in server thru rmi.. but i am not able to make calls from server to client.. will be glad if anyone can explain this with an easy example

thnx..

[Nitesh Kant]

Originally posted by simranjit singh:
my client is able to use functions stored in server thru rmi.. but i am not able to make calls from server to client.. will be glad if anyone can explain this with an easy example

thnx..

When you say you are "not able to", it means that you get an exception or you can not figure out how to do that?
Well, if there is an exception then a stacktrace will help however, if you can not figure it out, then, the point is that the client should also expose its Remote interface for others(server) to call it.
So, in this scenario, there is no clear role separation of a client and server, both the objects act as both client and server.

[Ulf Dittmer]

... so the question becomes: Is the client set up to act as an RMI server as well?

[simranjit singh]

i can not figure out how to do that...

i tried but i landed up writing my output message on server sides cmd prompt(that according to me should have been printed on client sides cmd prmpt) and if i try putting up my that message in my client sides window,(textarea) it gives me nullpointer and for this i know why since it could not find a reference to that client window in which it should print.

server code:

package vcc;
 
imports.... 
 
public class serverRMIImpl extends javax.swing.JFrame implements Remote,serverRMIIntf {
    
     private static final int PORT = 10005;
     private static String serverIP="127.0.0.1";
     //private static serverRMIIntf rmiServer;
     private static clientRMIIntf clientrmiIntf;
     ArrayList<clientRMIIntf> clientwindows;
     public serverRMIImpl() {
        super();
        initComponents();
        clientwindows = new ArrayList<clientRMIIntf>();
    }
    
        public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new serverRMIImpl().setVisible(true);
            }
        });
        try
          {
             serverRMIIntf rmiServer = new serverRMIImpl();
             
                          
             UnicastRemoteObject.exportObject( ((serverRMIIntf)rmiServer) );
            
             Naming.rebind( "//" + serverIP + "/" + "serverRMIIntf", rmiServer );
 
             System.out.println( "Bindings Finished" );
 
             System.out.println( "Waiting for Client requests" );
 

          }
          catch ( java.rmi.UnknownHostException uhe )
          {
             System.out.println( "The host computer name you have specified, " + serverIP + " does not match your real computer ip." );
 
          }
          catch ( RemoteException re )
          {
             System.out.println( "Error starting service" );
             System.out.println( "" + re );
             re.printStackTrace();
          }
          catch ( MalformedURLException mURLe )
          {
             System.out.println( "Internal error" + mURLe );
          }
 
        
    }
    
public boolean chkDB(String username, String password) throws RemoteException {
        //checking username password request from login form
        }
    
     public boolean newUserLoggedIn(String username, String clientip) throws RemoteException {
         //inserting into database values in currentinfo(table name), a new user has logged in ---- called from login form
         // if returned true --- will open a client window          
     }
        
     public boolean sendFirstMessage(String uname, String clientip) throws RemoteException {
         // first message to serverRMIImpl and all clients currently logged in.
         // uname is username of client who is sending message to all nad clientip is its ip 
                  Iterator i = clientwindows.iterator();
int numberofClienti = clientwindows.size();
System.out.println(numberofClienti + " i was here");
                
while (i.hasNext()) {
clientRMIIntf cl = (clientRMIIntf) i.next();
                        System.out.println("doing.... ");
cl.messageReceived(uname, "New User logged in");

}
         
         return true;
     }
      
    public void registerForCallback(clientRMIIntf cl) throws RemoteException {
if (!clientwindows.contains(cl)) {
clientwindows.add(cl);
System.out.println("### New client registered.");
}
}
 

public void unregisterForCallback(clientRMIIntf cl) throws RemoteException {
if (clientwindows.remove(cl)) {
System.out.println("### Client unregistered.");
} else {
System.out.println("### Unable to unregister client.");
}
}
   
 
    
}

server Interface:

 
package vcc;
 
import java.rmi.*;
 
public interface serverRMIIntf extends Remote {
    public boolean chkDB(String username, String password) throws RemoteException;   
    public boolean newUserLoggedIn(String username, String clientip) throws RemoteException;
    public boolean sendFirstMessage(String uname, String clientip) throws RemoteException;
    public void registerForCallback(clientRMIIntf cl) throws RemoteException;
    public void unregisterForCallback(clientRMIIntf cl) throws RemoteException ;
}

client:

 
package vcc;
 
import java.io.*;
import java.net.*;
import java.rmi.server.UnicastRemoteObject;
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import java.rmi.*;
 
public class clientRMIImpl extends javax.swing.JFrame implements Remote,clientRMIIntf {
    String serverIP, clientIP, USERNAME;
    private serverRMIIntf serverrmiIntf;
    private static final int PORT = 10005;
    
       
    public clientRMIImpl() throws RemoteException{
        super();
    }
    
    public clientRMIImpl(String uname, String serverip, String clientip) {
        USERNAME = uname;
        serverIP = serverip;
        clientIP = clientip;
        initComponents();
        this.setVisible(true);        
                
        try
          {
             clientRMIIntf rmiClient = new clientRMIImpl();
             System.out.println( "Exporting the client" );
             UnicastRemoteObject.exportObject((clientRMIIntf)rmiClient);
             String  serverName = "rmi://" + serverip + "/serverRMIIntf" ;
             
             System.out.println( "Looking up Service at: " + serverName );
 
             try
             {
                serverrmiIntf = (serverRMIIntf)Naming.lookup( serverName );
             }
             catch ( Exception e )
             {
                System.out.println( "" + e );
                e.printStackTrace();
             }
                          
            clientRMIIntf clObject = new clientRMIImpl();
            System.out.println("m here...");
            serverrmiIntf.registerForCallback(clObject);
            System.out.println("### Registering for callback complete");
                        
            System.out.println("hello i am jus back..");
             
             boolean resultFromDB = serverrmiIntf.sendFirstMessage(USERNAME,clientip);
             if(resultFromDB==true)
             {
                 System.out.println( "We have been registered!" );
             }
             else
             {
                 System.out.println( "Sorry, Error in registering!" );
             }
 
          }
          catch ( RemoteException re )
          {
             System.out.println( "" + re );
          }
        }
        
    public void messageReceived(String fromUsername, String message)  throws RemoteException {
        System.out.println("your final message: "+fromUsername+": "+message);
        try{
            jTextArea1.append(fromUsername+": "+message);            
        }
        catch(Exception ex)
        {
            ex.printStackTrace();
        }
        
    }   
}
 

client interface file:

 
package vcc;
 
import java.rmi.*;
 
public interface clientRMIIntf extends Remote {
   public void messageReceived(String fromUsername, String message) throws RemoteException;
}
 

login file m using:

 
package vcc;
 
import java.io.*;
import java.net.*;
import java.util.*;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
import java.sql.*;
import java.rmi.*;
 
public class login extends javax.swing.JFrame {
    JFrame f = new JFrame();
    String serverip, clientip, username, password;
    boolean newUserAdded=false;
     private static final int PORT = 10005;
     serverRMIIntf serverrmiIntf;
    
    public login() {
        initComponents();
    }
    
    
    private void jButton3ActionPerformed(java.awt.event.ActionEvent evt) {
 
    jPasswordField1.setText("");
        jTextField2.requestFocusInWindow();
    }
 
    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt) {
        jTextField2.setText("");
        jPasswordField1.setText("");
        jTextField2.requestFocusInWindow();
    }
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {        username=jTextField2.getText();        
        password=jPasswordField1.getText();        
        try {
            String  serverName = "rmi://" + serverip + "/serverRMIIntf" ;
 
             System.out.println( "Looking up Service at: " + serverName );
 
             try
             {
                serverrmiIntf = (serverRMIIntf)Naming.lookup( serverName );
             }
             catch ( Exception e )
             {
                System.out.println( "" + e );
             }
            
            boolean resultFromDB = serverrmiIntf.chkDB(username, password);
            if(resultFromDB==true)
            {
                setVisible(false);
                try {
                    InetAddress addr = InetAddress.getLocalHost();
                    System.out.println(addr);
                    // Get IP Address
                   String ipAddr = addr.getHostAddress();
                    System.out.println(ipAddr);
                    clientip = ipAddr;
                    
                } catch (Exception e) {
                    System.out.println("Exception: " + e);
                }
                
                try {
                    newUserAdded = serverrmiIntf.newUserLoggedIn(username,clientip);            
                }
                catch(Exception e) {
                    System.out.println("Exception: " + e);
                }
                if(newUserAdded==true)
                {
                    clientRMIImpl newclientwindow = new clientRMIImpl(username,serverip,clientip);
                }
            }
            else
            {
                JOptionPane.showMessageDialog(f,"Login Failed, Check Username, password and then try again..","DBResult",JOptionPane.OK_OPTION);
                jTextField1.requestFocusInWindow();
            }
        }
        catch(Exception e) {
            System.out.println("Exception: " + e);
        }
    }
 
    private void formWindowOpened(java.awt.event.WindowEvent evt) {
        jTextField1.requestFocusInWindow();
    }
 
    private void jPasswordField1KeyPressed(java.awt.event.KeyEvent evt) {//GEN-FIRST:event_jPasswordField1KeyPressed
        int m=evt.getKeyCode();
        if(m==evt.VK_ENTER) {
            jButton1.doClick();
        }
    }//GEN-LAST:event_jPasswordField1KeyPressed
 
    private void jTextField2KeyPressed(java.awt.event.KeyEvent evt) {//GEN-FIRST:event_jTextField2KeyPressed
         int m=evt.getKeyCode();
         if(m==evt.VK_ENTER) {            
            jPasswordField1.requestFocusInWindow();            
        }
    }//GEN-LAST:event_jTextField2KeyPressed
 
    private void jTextField1KeyPressed(java.awt.event.KeyEvent evt) {//GEN-FIRST:event_jTextField1KeyPressed
        int m=evt.getKeyCode();
        if(m==evt.VK_ENTER && !jTextField1.getText().isEmpty()) {
            serverip = jTextField1.getText(); 
            jTextField2.setEnabled(true);
            jPasswordField1.setEnabled(true);
            jButton1.setEnabled(true);
            jButton2.setEnabled(true);
            jButton3.setEnabled(true);
            jTextField2.requestFocusInWindow();
        }
    }//GEN-LAST:event_jTextField1KeyPressed
    
   public static void main(String args[]) {
        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new login().setVisible(true);
            }
        });
    }
   }
 

will be glad if you people can tellme where i am going wrong or what i can do to correct my code..

thanks

[Nitesh Kant]

I am not very sure whether this code runs with the client and server running in two different JVMs.
Well, i do not have any idea about Swing, but i am very skeptical about this code:

 
 
            clientRMIIntf rmiClient = new clientRMIImpl(); // Instance 1
            System.out.println( "Exporting the client" );
            UnicastRemoteObject.exportObject((clientRMIIntf)rmiClient);
            /*Code removed for readability */                          
            clientRMIIntf clObject = new clientRMIImpl(); // Instance 2
            System.out.println("m here...");
            serverrmiIntf.registerForCallback(clObject);

What you are doing is that you are exporting a different object (Instance 1)and registering a different object with the server(Instance 2).
This can only work when, the client and server are running in the same jvm when the actual instance of the client is passed to the server instead of the stub. Otherwise, it should give a Marshalling exception.
Anyways, i think if you pass instance 1 in the registerForCallback method, it should work.
I leave it to you to find out as to why, the message you expected to print on the client was printing on the server(assuming they run on same JVM)

[simranjit singh]

//clientRMIIntf clObject = new clientRMIImpl();
            System.out.println("m here...");
            serverrmiIntf.registerForCallback(rmiClient);
            System.out.println("### Registering for callback complete");    

used this.. again the null pointer exception.. i cannot figure out where i am going wrong..


this jtextArea is giving error

 public void messageReceived(String fromUsername, String message)  throws RemoteException {
        System.out.println("your final message: "+fromUsername+": "+message);
        try{
            jTextArea1.append(fromUsername+": "+message);            
        }
        catch(Exception ex)
        {
            ex.printStackTrace();
        }
        
    }

Stacktrace :

java.lang.NullPointerException
        at vcc.clientRMIImpl.messageReceived(clientRMIImpl.java:238)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:305)
        at sun.rmi.transport.Transport$1.run(Transport.java:159)
        at java.security.AccessController.doPrivileged(Native Method)
        at sun.rmi.transport.Transport.serviceCall(Transport.java:155)
We have been registered!
        at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:535)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:790)
        at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:649)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:885)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:907)
        at java.lang.Thread.run(Thread.java:619)
 

problem of getting that message on server window has been solved.. thanks alot..
will be glad if this nullpointer can also be removed..

[Nitesh Kant]

Firstly, adding to my previous post, since JFrame is Serializable, so the rmi call succeeded even if the server and client were on different JVMs. The newly created ClientImpl was serialized and sent across to the server JVM.
Ok, now for the null pointer exception.
From the stack trace, i can hardly make out anything since i dont have the line numbers in the code. However, the messageReceived() method does not have anything but a system.out and jtextArea1.append(). I am curious as to where jtextarea1 is defined/initialized. The only source of an NPE can be that jtextarea1 is null.(Assuming that fromUsername and message are not null)
Excuse me if i am missing out something related to swing in the above as swing is latin and greek to me

[simranjit singh]

jTextArea is defined / initialized when initcomponents() method in clientRMIImpl is called. i am developing my project in netbeans 5.5, jdk 1.6

initcomponents i guess you can see in the clientRMIImpl.java code in the code above..

what can i do to pass a reference of that window to this jtextArea when i get that reply from server?
System.out.print just above is working just fine.