Creating A Model For An Air-line Reservation Using RMI

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Example:

The following example develops a simple block of an Airline Reservation System. A User Interface, captures the flight number. On clicking the 'Seat Availability' button, a method on the Server is called. This method displays the flight number on the Server's console and returns the number of seats available for the specified flight. The number is then displayed in the results text area on the User Interface at the client. If information fot the specified flight is not available, the number returned is zero.

To create the above application the following steps needs to be done:

•   Create an Access database file called 'aireline.mdb'
•   Create a table called 'Flight' within the above database file i.e. 'airline.mdb'.

The following defines the table structure for the Airline Reservation Application in access.

Table Name : Flight
Primary Key : FlightNo

Column Definition:

Diagram 23.3 Flight Table

Test Records:

Diagram 23.4 Test Records of Flight Table

  To allow the User Interface to communicate with the database, a DSN with the     name 'airline' needs to be created.

  The following classes and interfaces are needed for server application:

• AirlineInterface: Defines the methods that are remotely accessible.
• AirlineServer: Implements the methods declared in the interface that will be invoked by the remote client.
• AirlineClient: The User Interface, which captures user data calls the remote method that checks for the validation.

SERVER APPLICATION

Code for AirlineInterface.java

import java.rmi.*; public interface AirlineInterface extends Remote { public int bookSeat(String FlightNo) throws RemoteException; }

Compile the above code on the Server



This will create AirlineInterface.class.


Code for AirlineInterface.java

import java.rmi.*; import java.rmi.server.*; import java.rmi.registry.*; import java.util.*; import java.sql.*; public class AirlineServer extends UnicastRemoteObject implements AirlineInterface { String url = "jdbc:odbc:airline"; Connection conn; // Server Constructor public AirlineServer( ) throws RemoteException { System.out.println("Initializing the Server"); } // The bookSeat() method. public int bookSeat(String FlightNo) { int seatdtls=0; System.out.println("Flight is " + FlightNo); try { // Load the Driver Class.forName("sun.jdbc.odbc.JdbcOdbcDriver"); // Pass the static fields containing the data source name conn = DriverManager.getConnection(url); Statement stmt = conn.createStatement(); ResultSet rs= stmt.executeQuery("Select Seats from Flight where Flightno = '" +FlightNo+ "'"); while (rs.next()) { seatdtls = rs.getInt("Seats"); } } catch(Exception excp) {} if (seatdtls > 0 ) return seatdtls; else return 0; } //End of bookSeat() method // Implement the main() method public static void main(String args[]) { try { // create an instance of the Server object to export AirlineServer arlnServer = new AirlineServer(); Naming.rebind("airlineServ", arlnServer); /* airlineServ is the name under which the server registers itself in the RMI registry. */ System.out.println("Server Ready"); } // End of try block catch (RemoteException RemotExcp) { System.out.println("Remote Server Error: " + RemotExcp.getMessage()); System.exit(0); } catch (Exception excp) { System.out.println("Error: " + excp.getMessage()); System.exit(0); } } // End of main() method } // End of Server class

Compile the above code on the Server

This will create AirlineServer.class.

This will create the stubs and skeltons:

AirlineServer_stub.class and AirelineServer_skel.class



CLIENT APPLICATION

Code for AirlineClient.java

import java.rmi.*; import java.rmi.registry.*; import java.awt.*; import java.awt.event.*; public class AirlineClient extends Frame implements ActionListener { Button btnBookSeat = new Button("Seat Availability"); // Create Labels Label lblFlightNo = new Label("Flight No:"); Label lblResults = new Label("Results:"); // Create a text area TextArea taResults = new TextArea(); // Create Text Items TextField txtFlightNo = new TextField(20); // Constructor of the AirlineClient public AirlineClient() { super("Airline Reservation System (Remote Client - RMI)"); setLayout (null); lblFlightNo.setBounds(20,50,55,25); add(lblFlightNo); txtFlightNo.setBounds(150,50,100,25); add(txtFlightNo); lblResults.setBounds(20,155,100,25); add(lblResults); taResults.setBounds(150,155,400,200); add(taResults); btnBookSeat.setBounds(175,375,250,25); add(btnBookSeat); // Add listeners for the buttons btnBookSeat.addActionListener(this); enableEvents(AWTEvent.WINDOW_EVENT_MASK); } // End of the remote class constructor AirlineClient() public void processWindowEvent(WindowEvent winEvt) { if(winEvt.getID() == WindowEvent.WINDOW_CLOSING) { setVisible(false); dispose(); System.exit(0); } } // To trap events for each buttons public void actionPerformed(ActionEvent actEvt) { if (actEvt.getSource() == btnBookSeat) { seatcheck(); } } // End of actionPerformed() method public void seatcheck() { String Flight=txtFlightNo.getText(); int val; try { String ServerURL = "//127.0.0.1/airlineServ"; AirlineInterface alIntf = (AirlineInterface)Naming.lookup(ServerURL); val = alIntf.bookSeat(Flight); if (val == 0) { taResults.setText("No seats available for flight " + Flight); } else { taResults.setText("The seats available on flight " + Flight + " are " + val); } } catch(Exception excp) { System.out.println("Exception: "+excp); } } // AirlineClient main() method public static void main(String [] args) { // Invoke the constructor of the AirlineClient class AirlineClient rmtAirline = new AirlineClient(); rmtAirline.setVisible(true); rmtAirline.setSize(600,500); } // End of main() method } // End of AirlineClient class

Compile the above code on the Client (in a separate console window)

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This will create AirlineClient.class. Start the rmiregistry on the Server.

Execute the server program on the server.

Diagram 23.5 Output of AirlineServer (at the Console)

Execute the client program on the client

Diagram 23.6 Output of AirlineClient.class when seats are available(User Interface)

Diagram 23.7 Output of AirlineClient.class when no seats are available(User Interface)