LAB 1 CSIS0402 1

Briefing on

Assignment One & RMI Programming

February 13, 2007

LAB 1 CSIS0402 2

Lab One Organization

RMI Introduction A Simple Example Recap of RMI Components

Assignment One Overview System Architecture Remarks

Lab Exercise on RMIReference

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Introduction to RMI

Often consists of 2 separate programs: a server and a clientProvide 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.

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A Simple RMI Example

Skeleton Stub

ClientServer

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.

Network

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.

The skeleton de-marshals the data and makes the method call on the actual server object.

The skeleton gets the return value back from the server object, marshals the return value and sends to the stub.

RMIRegistry

Server creates a remote object , registers the service to RMIRegistry and passes the object reference to the registry

Client invokes a method on the stub

The stub de-marshals the return value and returns it to the client.

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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

StubActs as the local representative for the remote objectImplements the same remote interface as the remote objectMaintains a socket connection to the remote object’s JVM automaticallyResponsible for marshalling and de-marshalling data on the client side

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SkeletonA 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

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Assignment One

Overview

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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

PersonalCan be viewed and downloaded by the file owner only.

GroupPublic

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.

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GUI

From Java.Swing:

- JFrame

- JSplitPane

- JTree

- JTextArea

- JButton

- JLabel

…

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System Architecture

OnlineDriveServer.java

-Server interface that describes the behavior of the server

OnlineDriveServerImp.java- Class that implement the server functions

OnlineDriveClientImp.java- Client application that maintains the Chatroom functionalilities

implements

Server side components Client side component

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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>

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Lab Exercise on RMI

CountServer

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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.

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System Architecture

CountServerImp.java

CountServer.java

CountClientImp.java

extends

CountServer interface that describes the behavior of the server

Class that implements the server functions Swing client

application that captures user’s input, sends to the server and displays server’s reply to the GUI.

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CountServer.java(Interface class of the server)

…

import java.rmi.*;

public interface CountServer extends Remote {

public int countMsg(String msg) throws RemoteException; }

Return types of the remote method

Exception thrown by RMI to signal that something unforeseen has happened at the network level

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CountServerImp.java(Implementation class of the server)

import java.rmi.*;import java.rmi.server.*;

public class CountServerImp extends UnicastRemoteObject implements CountServer {

public int countMsg(String msg) throws RemoteException {return msg.length();

}

Automatically relates the instance into the RMI runtime and listens for remote method calls.

Return the string to the remote client

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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’

CountServerImp.java(2)(Implementation class of the server)

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CountClientImp.java(Implementation class of the client)

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);}

}

Swing Application

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

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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);

} }

…

Remotely invoke the RMI Server and send the message to it

Register the action listener for send button

CountClientImp.java(2)(Implementation class of the client)

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public static void main( String args[] ) {…

try{CountClientImp client = new CountClientImp();

}catch( Exception e ){e.printStackTrace();

}}

Create a CountClientImp object

CountClientImp.java (3)(Implementation class of the client)

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Lab Exercise - How to start

Download the lab1.zip from the course homepageCompile the files by

javac *.java

Generate stub and skeletonrmic CountServerImp

Start the RMI registry (keep on running)rmiregistry

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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

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Lab Exercise - How to start(3)

Test the applicationType a message in the text area on the Client GUI, click “Count Message”.

Check if the count is returned and displayed on the GUI.

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Reference (1)

Swing (for the GUI) in Java Tutorialhttp://java.sun.com/docs/books/tutorial/uiswing

Getting start with Swinghttp://java.sun.com/docs/books/tutorial/uiswing/start/index.html

Layout Managerhttp://java.sun.com/docs/books/tutorial/uiswing/layout/index.html

Event Listenerhttp://java.sun.com/docs/books/tutorial/uiswing/events/index.html

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Reference (2)

RMI in Java Tutorialhttp://java.sun.com/docs/books/tutorial/rmi/overview.html

RMI course from jGuruhttp://developer.java.sun.com/developer/onlineTraining/rmi/RMI.html#JavaRMIArchitecture