Pushing Data from the RMI Server

[Vinodh Sa]

Hi All,

I m totally new to RMI. I started learning RMI yesterday only, when i came through the RMI chapter in J2EE Bible.

I m facing one problem when i m using the concept of "Pushing Data from the RMI server".

I m getting the "Access denied" exception in client side when i try to call a method of server side code, inspite of having the security.policy file.

Can anyone help me in this ?

Code:

[b] [u]File : FlightServer2.java[/u][/b]   
          import java.rmi.*;
          public interface FlightServer2 extends java.rmi.Remote
          {
	public void registerClient(RefreshScreen client)throws java.rmi.RemoteException;
	public String getDepartureTime(String flightNo)throws java.rmi.RemoteException;
	public String getArrivalTime(String flightNo)throws java.rmi.RemoteException;
          }

[b][u]File : FlightServerImpl2 [/u][/b]

import java.rmi.*;
import java.rmi.server.*;
import java.util.Hashtable;
public class FlightServerImpl2 extends UnicastRemoteObject implements FlightServer2
{
	private Hashtable arrivals = new Hashtable();
	private Hashtable departures = new Hashtable();

	public FlightServerImpl2() throws RemoteException
	{
		super();
		arrivals.put("C01208","3:20PM");
		arrivals.put("C01331","8:00PM");
		arrivals.put("C03450","6:05PM");
		departures.put("C01209","4:20PM");
		departures.put("C01200","9:15PM");
		departures.put("C00456","10:05PM");
	}

	private RefreshScreen client;

	public void registerClient(RefreshScreen client)throws java.rmi.RemoteException
	{
		System.out.println("In RegisterClient()");
		this.client = client;
		System.out.println("Calling startClientUpdates()");
		startClientUpdates();
	}

	private void startClientUpdates() throws java.rmi.RemoteException
	{
		System.out.println("In startClientUpdates()");
		while(true)
		{
			try
			{
				Thread.sleep(10000);
			}
			catch(InterruptedException e)
			{
				e.printStackTrace();
			}
			client.updateFlightInfo(arrivals);
		}
	}

	public String getArrivalTime(String flightNo)throws RemoteException
	{
		String arrTime = null;
		arrTime = (String) arrivals.get(flightNo);
		return arrTime;
	}

	public String getDepartureTime(String flightNo)throws RemoteException
	{
		String deptTime = null;
		deptTime = (String) departures.get(flightNo);
		return deptTime;
	}
}



[b][u]File : FlightClient2 [/u][/b]

import java.util.Date;
import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;
import java.util.Hashtable;
import java.util.Vector;
import java.io.Serializable;

public class FlightClient2 implements RefreshScreen
{
	public void updateFlightInfo(Hashtable flightInfo)
	{
		System.out.println("Flight data as of " + new Date() + ": "+flightInfo);
	}

	public static void main(String args[])
	{
		FlightClient2 fc = new FlightClient2();

		try
		{
			if(null == System.getSecurityManager())
			{
				System.setSecurityManager(new RMISecurityManager());
			}
			System.out.println("Exporting Client Object");
			UnicastRemoteObject.exportObject(fc);
			System.out.println("Lookup Server Object");
			FlightServer2 myServer = (FlightServer2) Naming.lookup("rmi://172.26.199.45:6000/FlightService2");
			System.out.println("Registering Client");
			myServer.getArrivalTime("C01208");
			myServer.registerClient(fc);
			System.out.println("All Done");
		}
		catch(Exception e)
		{
			System.out.println(e.getMessage());
		}

		System.out.println("Flight Client 2 is waiting for the flight info updates from the server...");
		while(true){}//Keep the Client alive
	}
}


[b][u]File : RefreshScreen.java [/u][/b]

import java.rmi.*;
import java.util.Hashtable;
public interface RefreshScreen extends java.rmi.Remote
{
	void updateFlightInfo(Hashtable flightsInfo) throws RemoteException;
}

[b][u]File : StartFlightServer2.java[/u][/b]
import java.rmi.*;
import java.rmi.registry.LocateRegistry;
public class StartFlightServer2
{
	public static void main(String args[])
	{
		try
		{
			FlightServerImpl2 fsi = new FlightServerImpl2();
			Naming.rebind("rmi://172.26.199.45:6000/FlightService2", fsi);
			System.out.println("Flight Service 2 is waiting for the requests on port 6000 ...... ");
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
	}
}

[b][u]File : security.policy[/u][/b]
grant
{
	permission java.net.SocketPermission "*:1024-", "connect";
};
            

After starting the rmi registry and the FlightServer2, i m running the flight client2 using the following command

java -Djava.security.policy=security.policy FlightClient2

But i m getting, "Access Denied" exception after abt 30 seconds.....

Any one please help......

[miguel roxo]

hi Vinodh,
why are you exporting the client?
"UnicastRemoteObject.exportObject(fc); " in line 102;

I'm guessing you're trying to do something asynchronous with your RMI app, but to do that you just have to use a callback in the client and pass the reference to the server and it will notify the client when it's done; you can Google more info about callback easily;
But usually RMI works in a direct way:
-client request the server reply an object;

And the server is the one who as to be exported not the client;

You may do one of these:
- if your server extends UnicastRemoteObject, you don't need to export it;
- or else:
server = new ClassServer();
RemoteInterfaceExtendedByServerClass stub=(RemoteInterfaceExtendedByServerClass) UnicastRemoteObject.exportObjct(server);

This code is follows one of the options above.
Registry registry =LocateRegistry.createRegistry(port_where_your_server_will_listen_for_requests);
registry.rebind("the_name_of_the_RMI_service",server);
while(true){
Thread.currentThread();
Thread.sleep(100);
}

Now the server is registed in the service names and binded to a port;

In the client you just have to do this:

RemoteInterfaceExtendedByServerClass client = null;
Registry registry = LocateRegistry.getRegistry("your_server_ip or name, if same machine then localhost",port_where_your_server_will_listen_for_requests);
client = (RemoteInterfaceExtendedByServerClass) registry.lookup(RemoteInterfaceExtendedByServerClass);

and after this you can call any function in your RemoteInterfaceExtendedByServerClass interface;

Regards, hope this helps you.
Miguel Roxo