Implementing Servers

• We're going to make a client-server program that gives us the artist of a song when we provide the song type.
• We can either run this entirely on one computer, or we can run the client on one computer and the server on another.
• We'll use three classes in this project.
• FavoriteDisco is our client GUI.  It extends JFrame and has JList, JScrollPane, JComboBox, JButton, JLabel and ClientSocket objects.
• ClientSocket is accessed by FavoriteDisco to connect to the server.
• It has host and port attributes.  It uses those to open up a connection to the server.  When it has this connection, it writes a string to the PrintWriter object, which serializes the String and sends it over the socket connection.
• Then, it patiently awaits a response from the server.  The response will be a String, which is the corresponding artist of the song passed above.  It gets this response over the BufferedReader object, and reads it in.
• It returns this response to FavoriteDisco, which displays the artist of the song.
• DiscoServer is our server object.
• It waits for a connection on port 8089.  When it gets a client connection, it reads in the data (String representing the song), decides what to send back, then sends it back.
• It uses the BufferedReader and PrintWriter objects just like our client does.
• Since the client and the server are two separate programs, how do we run them?
• It's not too difficult, actually.  We select the server first, and choose execute.  In Forte'/NetBeans, that brings us to the Running tab.  Then, we click the Editing tab again, select FavoriteDisco, and choose execute.
• This gives us two running processes in our Execution window.
• To terminate these processes, we have to right-click on them in the Execution window and click "Terminate".
• Please note, this is a simple demonstration of sockets.  By no means is it optimized.
• The screen capture:

• The Source (important changes in blue):
• FavoriteDisco

package networking;

import javax.swing.DefaultListModel;
import javax.swing.JComboBox;
import java.io.*;
import java.net.*;

/**
 *
 * @author  default
 */
public class FavoriteDisco extends javax.swing.JFrame {

    DefaultListModel model;
    ClientSocket client;
 
    /** Creates new form FavoriteDisco */
    public FavoriteDisco() {
        initComponents();
        model = new DefaultListModel();
        lstLyrics.setModel(model);
        client = new ClientSocket();
    }

    /** This method is called from within the constructor to
     * initialize the form.
     * WARNING: Do NOT modify this code. The content of this method is
     * always regenerated by the Form Editor.
     */
    private void initComponents() {
        jScrollPane1 = new javax.swing.JScrollPane();
        lstLyrics = new javax.swing.JList();
        jPanel1 = new javax.swing.JPanel();
        lblFavorite = new javax.swing.JLabel();
        String[] arrDisco = new String[5];
        arrDisco[0] = "YMCA";
        arrDisco[1] = "Yowsah, Yowsah, Yowsah";
        arrDisco[2] = "You Make Me Feel";
        arrDisco[3] = "That's The Way";
        arrDisco[4] = "Stayin Alive";
        cboDisco = new JComboBox(arrDisco);
        btnGo = new javax.swing.JButton();

        addWindowListener(new java.awt.event.WindowAdapter() {
            public void windowClosing(java.awt.event.WindowEvent evt) {
                exitForm(evt);
            }
        });

        jScrollPane1.setViewportView(lstLyrics);

        getContentPane().add(jScrollPane1, java.awt.BorderLayout.CENTER);

        lblFavorite.setText("What's your favorite disco?");
        jPanel1.add(lblFavorite);

        jPanel1.add(cboDisco);

        btnGo.setText("Go");
        btnGo.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                btnGoActionPerformed(evt);
            }
        });

        jPanel1.add(btnGo);

        getContentPane().add(jPanel1, java.awt.BorderLayout.NORTH);

        pack();
    }

    private void btnGoActionPerformed(java.awt.event.ActionEvent evt) {
        // Get the song string
        String song = (String) cboDisco.getSelectedItem();
 
        // Send this string to the server via the ClientSocket class.
        // Get back the artist.
        String artist = client.connect(song);

        // Add this to our list.
        model.addElement(song + " is performed by " + artist);
 
    }

    /** Exit the Application */
    private void exitForm(java.awt.event.WindowEvent evt) {
        System.exit(0);
    }

    /**
    * @param args the command line arguments
    */
    public static void main(String args[]) {
        new FavoriteDisco().show();
    }
 

    // Variables declaration - do not modify
    private javax.swing.JList lstLyrics;
    private javax.swing.JButton btnGo;
    private javax.swing.JComboBox cboDisco;
    private javax.swing.JLabel lblFavorite;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JPanel jPanel1;
    // End of variables declaration

}
 

• ClientSocket

package networking;

import java.io.*;
import java.net.*;

/**
 *
 * @author  default
 */
public class ClientSocket {

    String host = "127.0.0.1";
    int port = 8089;
 
    /** Creates a new instance of ClientSocket */
    public ClientSocket() {
    }
 
    public ClientSocket(String host, int port) {
        this.host = host;
        this.port = port;
    }
 
    public String connect(String song) {
        // The StringBuffer will contain our result that we will change to a String and return.
        StringBuffer result = new StringBuffer();
        try {
            // Create a socket.
            Socket socket = new Socket(host, port);
 
            // Create a PrintWriter to send our song title to the server.
            PrintWriter out = new PrintWriter(socket.getOutputStream());
            out.print(song);
            out.print("\r\n");
            // Tell it to go ahead and send.
            out.flush();
 
            // Create a buffered reader and input stream to read the response.
            // We can get the input stream from the socket, and we can pass that to the buffered reader
            // constructor.
            BufferedReader in = new BufferedReader(new InputStreamReader(socket.getInputStream()));
            boolean moreData = true;
 
            // Read while we have information to read.
            while(moreData) {
                // Read a line from the buffered reader.
                String line = in.readLine();
 
                // Read the data, or let the loop know we're finished.
                if (line == null) {
                    moreData = false;
                } else {
                    if (line.equals("Connected.")) { /* just digreguard this. */ }
                    result.append(line);
                } // end if.
            } // end for.
        // Handle exceptions.
        } catch (NumberFormatException e) {
            System.out.println("Enter the port as a number, please.  Message: " + e.getMessage());
            e.printStackTrace();
        } catch (IOException e) {
            System.out.println("IOException caught while attempting connection.  Message: " + e.getMessage());
            e.printStackTrace();
        }
        return result.toString();
    }
 
    public static void main(String args[]) {
 
    }

}
 

• DiscoServer

package networking;

import java.io.*;
import java.net.*;

/**
 *
 * @author  default
 */
public class DiscoServer {

    /** Creates a new instance of DiscoServer */
    public DiscoServer() {
    }
 
    public static void main(String args[]) {
        String artist = "invalid";
        try {
            // establish server socket on port 8089.
            ServerSocket s = new ServerSocket(8089);

            // A continuous loop to accept connections.
            boolean blnMore = true;
            while (blnMore) {
                    // Wait for connection from client.
                    // When we have a connection from a client, this will return a socket object.
                    Socket incoming = s.accept();

                    System.out.println("Socket Accepted");

                    // Get the buffered reader.
                    BufferedReader in = new BufferedReader(new     InputStreamReader(incoming.getInputStream()));

                    // Get a print writer to send output.
                    PrintWriter out = new PrintWriter(incoming.getOutputStream(), true);

                    // out.println("Connected.");
 
                    // Get data from the client.
                    boolean complete = false;
                    String line =  in.readLine();
                    if (line == null) {
                        // we're finished.
                        complete = true;
                        artist = "Complete";
                    } else {
                            System.out.println("Line: " + line);
                            // pardon my if test.
                            if(line.equals("YMCA")) {
                                artist = "Village People";
                            } else if (line.equals("Yowsah, Yowsah, Yowsah")) {
                                artist = "Chic";
                            } else if (line.equals("You Make Me Feel")) {
                                artist = "Sylvester";
                            } else if (line.equals("That's The Way")) {
                                artist = "K.C. and the Sunshine Band";
                            } else if (line.equals("Stayin Alive")) {
                                artist = "Bee Gees";
                            } else if (line.equalsIgnoreCase("stop")) {
                                blnMore = false;
                            } else {
                                artist = "Connected";
                            }
 

                    }

                    // Send the response.
                    out.print(artist);
                    out.print("\r\n");
                    out.flush();

                    // Close the connection.
                    incoming.close();

            }
 
        } catch (Exception e) {
            e.printStackTrace();
        }
 
        // Call it again.
        DiscoServer.main(args);
    }
 

}

Sending e-mail

Created by:  Brandan Jones December 17, 2001