Briefing on Assignment One & RMI Programming

1. Briefing on Assignment One & RMI Programming February 13, 2007 CSIS0402

2. Lab One Organization • RMI • Introduction • A Simple Example • Recap of RMI Components • Assignment One • Overview • System Architecture • Remarks • Lab Exercise on RMI • Reference CSIS0402

3. Introduction to RMI • Often consists of 2 separate programs: a server and a client • Provide the mechanism by which the server and the client communicate and pass information back and forth. • Make the communication like making a method call inside a single process. CSIS0402

4. Client looks up the remote object by its name from the server’s registry and obtains a remote reference (i.e. the stub) of it. Server creates a remote object , registers the service to RMIRegistry and passes the object reference to the registry Server Client The stub de-marshals the return value and returns it to the client. The skeleton gets the return value back from the server object, marshals the return value and sends to the stub. The skeleton de-marshals the data and makes the method call on the actual server object. Client invokes a method on the stub The stub either creates a socket connection to the skeleton on the server or reuses a pre-existing connection. It marshals all the information associated to the method call, with name of method and arguments and sends to the skeleton. A Simple RMI Example RMIRegistry Skeleton Stub Network CSIS0402

5. Recap of RMI Components • RMIRegistry • Runs on a central server and functions like a phone book • Maps logical names to actual servers so that client programs can easily locate and use appropriate server applications • Stub • Acts as the local representative for the remote object • Implements the same remote interface as the remote object • Maintains a socket connection to the remote object’s JVM automatically • Responsible for marshalling and de-marshalling data on the client side CSIS0402

6. Skeleton • A server-side object responsible for • maintaining network connections with the stub • marshalling and de-marshaling data on the server side • Stubs and Skeletons are generated from the implementation class files by a command-line application called rmic CSIS0402

7. Assignment One Overview CSIS0402

8. A Simple File Hosting SystemOnlineDrive v1.0 • Offer a sort of "network storage" for personal backup, file access or file distribution • Support three sharing options • Personal • Can be viewed and downloaded by the file owner only. • Group • Public • In Assignment One, you only need to develop the GUI and the simplest mode of sharing: Personal. • You are required to use RMI to handle ALL communications between server and clients. CSIS0402

9. GUI • From Java.Swing: • JFrame • JSplitPane • - JTree • - JTextArea • - JButton • - JLabel • … CSIS0402

10. System Architecture • OnlineDriveServer.java • Server interface that describes the behavior of the server implements OnlineDriveServerImp.java- Class that implement the server functions OnlineDriveClientImp.java - Client application that maintains the Chatroom functionalilities Server side components Client side component CSIS0402

11. Remarks • Class names to be used… • Server class: OnlineDriveServerImp.java • Client class: OnlineDriveClientImp.java • RMIC for server • To generate stubs and skeletons • Make sure… • your server can be started by • > java <options> OnlineDriveServerImp • your client can be started by • > java <options> OnlineDriveClientImp <hostname> CSIS0402

12. Lab Exercise on RMI CountServer CSIS0402

13. CountServer Overview • A RMI application consists of • a RMI server and • a client swing application. • Client inputs a message and sends to the server. • Server receives the message, count the number of characters and return the count to the client. • Client displays the count on the GUI. CSIS0402

14. CountServer interface that describes the behavior of the server extends Class that implements the server functions System Architecture CountServer.java CountClientImp.java CountServerImp.java Swing client application that captures user’s input, sends to the server and displays server’s reply to the GUI. CSIS0402

15. CountServer.java(Interface class of the server) Exception thrown by RMI to signal that something unforeseen has happened at the network level … import java.rmi.*; public interface CountServer extends Remote { public int countMsg(String msg) throws RemoteException; } Return types of the remote method CSIS0402

16. CountServerImp.java(Implementation class of the server) Automatically relates the instance into the RMI runtime and listens for remote method calls. import java.rmi.*; import java.rmi.server.*; public class CountServerImp extends UnicastRemoteObject implements CountServer { public int countMsg(String msg) throws RemoteException { return msg.length(); } Return the string to the remote client CSIS0402

17. CountServerImp.java(2)(Implementation class of the server) public static void main( String args[] ) { … CountServerImp server = new CountServerImp();Naming.rebind( "//localhost/CountServer",server ); … } Create a CountServer object to provide services for clients Static method of the naming registry class to bind the server object to the specified host with the name ‘CountServer’ CSIS0402

18. CountClientImp.java(Implementation class of the client) Swing Application import java.rmi.*; … public class CountClientImp extends JFrame { … public CountClientImp( String hostname ) { serverLookup(); … } private void serverLookup(){ try{ server = (CountServer)Naming.lookup( "//localhost/CountServer" ); } catch(Exception e){ System.err.println(e); } } Call the static method of the Naming class to look up the remote server on the requested host and the specified server name Get a handle to the remote object CSIS0402

19. CountClientImp.java(2)(Implementation class of the client) JButton sendButton = new JButton(“Count Message"); … sendButton.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e){ sendMsgToServer(); } …private void sendMsgToServer(){ String msg = tArea.getText(); try{ Integer count = (Integer) server.countMsg(msg); msgCount = Integer.toString(count); tField.setText(msgCount); }catch(RemoteException re) { System.err.println(re); } } … Register the action listener for send button Remotely invoke the RMI Server and send the message to it CSIS0402

20. CountClientImp.java (3)(Implementation class of the client) public static void main( String args[] ) { … try{ CountClientImp client = new CountClientImp(); }catch( Exception e ){ e.printStackTrace(); } } Create a CountClientImp object CSIS0402

21. Lab Exercise - How to start • Download the lab1.zip from the course homepage • Compile the files by • javac *.java • Generate stub and skeleton • rmic CountServerImp • Start the RMI registry (keep on running) • rmiregistry CSIS0402

22. Lab Exercise - How to start(2) • Start the RMI Server in another command prompt • java CountServerImp • Start the client in another command prompt and connect to the server • java CountClientImp CSIS0402

23. Lab Exercise - How to start(3) • Test the application • Type a message in the text area on the Client GUI, click “Count Message”. • Check if the count is returned and displayed on the GUI. CSIS0402

24. Reference (1) • Swing (for the GUI) in Java Tutorial • http://java.sun.com/docs/books/tutorial/uiswing • Getting start with Swing • http://java.sun.com/docs/books/tutorial/uiswing/start/index.html • Layout Manager • http://java.sun.com/docs/books/tutorial/uiswing/layout/index.html • Event Listener • http://java.sun.com/docs/books/tutorial/uiswing/events/index.html CSIS0402

25. Reference (2) • RMI in Java Tutorial • http://java.sun.com/docs/books/tutorial/rmi/overview.html • RMI course from jGuru • http://developer.java.sun.com/developer/onlineTraining/rmi/RMI.html#JavaRMIArchitecture CSIS0402