Networking

Introduction In this lecture –Swing GUI component JEditorPane (view HTML docs) –Socket-based communications View networking like file I/O –Stream sockets When connection in place, data flows in continuous streams TCP protocol Preferred

Reading a File on a Web Server Reading files from a web server –JEditorPane ( javax.swing ) Can display text and HTML –Applets can only read files from original server

Reading a File on a Web Server –JEditorPane Method setPage( locationString ) –Download and display page –Hyperlinks Text, images, GUI components that access another document on web Generates HyperLinkEvent, notifies HyperLinkListener s 58 contents.setPage( location ); 32 contents = new JEditorPane(); 33 contents.setEditable( false ); 34 contents.addHyperlinkListener( 35 new HyperlinkListener() { 36 public void hyperlinkUpdate( HyperlinkEvent e )

Reading a File on a Web Server –Method getEventType Inner class EventType has three types –ACTIVATED - clicked –ENTERED - mouse over hyperlink –EXITED - mouse leaves hyperlink –Method getURL - returns URL of link 36 public void hyperlinkUpdate( HyperlinkEvent e ) 37 { 38 if ( e.getEventType() == 39 HyperlinkEvent.EventType.ACTIVATED ) 40 getThePage( e.getURL().toString() ); 41 }

Reading a File on a Web Server –setCursor( Cursor ) (inherited by J Frame ) Sets mouse cursor –static method getPredefinedCursor( int cursorType ) Returns Cursor cursorType –Cursor.WAIT_CURSOR –Cursor.DEFAULT_CURSOR 54 setCursor( Cursor.getPredefinedCursor( 55 Cursor.WAIT_CURSOR ) ); 68 setCursor( Cursor.getPredefinedCursor( 69 Cursor.DEFAULT_CURSOR ) );

1. import 1.1 extends JFrame 1.2 Constructor 1// Fig. 21.2: ReadServerFile.java 2// This program uses a JEditorPane to display the 3// contents of a file on a Web server. 4import java.awt.*; 5import java.awt.event.*; 6import java.net.*; 7import java.io.*; 8import javax.swing.*; 9import javax.swing.event.*; public class ReadServerFile extends JFrame { 12 private JTextField enter; 13 private JEditorPane contents; public ReadServerFile() 16 { 17 super( "Simple Web Browser" ); Container c = getContentPane(); enter = new JTextField( "Enter file URL here" ); 22 enter.addActionListener( 23 new ActionListener() { 24 public void actionPerformed( ActionEvent e ) 25 { 26 getThePage( e.getActionCommand() ); 27 } 28 } 29 ); JFrame inherits setCursor method, which our class can now use.

JEditorPane 1.4 addHyperLink Listener 2. Method getThePage 2.1 setCursor 2.2 setPage 34 contents.addHyperlinkListener( 35 new HyperlinkListener() { 36 public void hyperlinkUpdate( HyperlinkEvent e ) 37 { 38 if ( e.getEventType() == HyperlinkEvent.EventType.ACTIVATED ) getThePage( e.getURL().toString() ); 41 } 42 } 43 ); c.add( new JScrollPane( contents ), 46 BorderLayout.CENTER ); setSize( 400, 300 ); 49 show(); 50 } private void getThePage( String location ) 53 { setCursor( Cursor.getPredefinedCursor( 55 Cursor.WAIT_CURSOR ) ); try { contents.setPage( location ); 59 enter.setText( location ); 60 } 30 c.add( enter, BorderLayout.NORTH ); contents = new JEditorPane(); 33 contents.setEditable( false ); Create JEditorPane, register event handler (HyperLinkEvent s ). Get the URL of hyperlink, call utility method getThePage. Make sure user clicked hyperlink ( ACTIVATED ). Change cursor to a waiting state (downloading file). Display new page in JEditorPane.

3. main setCursor( Cursor.getPredefinedCursor( 69 Cursor.DEFAULT_CURSOR ) ); 70 } public static void main( String args[] ) 73 { 74 ReadServerFile app = new ReadServerFile(); app.addWindowListener( 77 new WindowAdapter() { 78 public void windowClosing( WindowEvent e ) 79 { 80 System.exit( 0 ); 81 } 82 } 83 ); 84 } 85} 61 catch ( IOException io ) { 62 JOptionPane.showMessageDialog( this, 63 "Error retrieving specified URL", 64 "Bad URL", 65 JOptionPane.ERROR_MESSAGE ); 66 }

Program Output

Establishing a Simple Server (Using Stream Sockets) Creating a Java server –Create ServerSocket object ServerSocket s = new ServerSocket( port, queueLength ); Register port number and set max number of waiting clients Binds server to port, waits for clients –Server listens indefinitely (blocks) for clients Socket connection = s.accept() Connections managed by Socket objects Returns Socket when connection established

Establishing a Simple Client (Using Stream Sockets) Creating a Java server –Get I/O objects for communication OutputStream - sends info to client InputStream - gets info from client Server's input stream is client's output stream, and vice versa –Use Socket object to get references to streams connection.getInputStream() connection.getOutputStream() –Methods write and read Send individual bytes

Establishing a Simple Client (Using Stream Sockets) Creating a Java server –Chaining stream types (sending objects and data, not bytes) ObjectInputStream input = new ObjectInputStream( connection.getInputStream() ) –Processing phase Server/client communicate using InputStream and OutputStream –Termination Transmission complete Method close (of Socket ) connection.close() –Networking appears as sequential file I/O Sockets simplify networking

Establishing a Simple Client (Using Stream Sockets) Creating a Java client –Create Socket to connect to server Socket connection = new Socket( serverAddress, port ) If successful, returns Socket –Else throws subclass of IOException –Get stream objects connection.getInputStream() connection.getOutputStream() Use chaining if transmitting objects and data, not pure bytes –ObjectInputStream, ObjectOutputStream

Establishing a Simple Client (Using Stream Sockets) Creating a Java client –Processing phase Communicate using stream objects –Termination Transmission complete connection.close() (close Socket ) –Client must determine when server done read returns -1 when eof found ObjectInputStream generates EOFException

Client/Server Interaction with Stream Socket Connections Upcoming program –Simple client/server chat application –Use stream sockets –Client connects, transmit String objects do-while loop to get input Event handler calls sendData method to send output –When either sends TERMINATE, connection terminates Server waits for next client –GUI:

Client/Server Interaction with Stream Socket Connections Server –Once connection ( Socket ) established getInetAddress() - returns InetAddress object getHostName() - returns client's host name –Create ObjectOutputStream flush() –Sends stream header to client –Required by client's ObjectInputStream 63 output = new ObjectOutputStream( 64 connection.getOutputStream() ); 65 output.flush(); 60 connection.getInetAddress().getHostName() );

Client/Server Interaction with Stream Socket Connections –Send/receive data Method sendData called by event handler Buffer flushed after every transmission –Sets cursor position to end of text Allows JTextArea to scroll with text –Server processes single connection at a time More likely to have separate threads for each connection 108 private void sendData( String s ) 109 { 111 output.writeObject( "SERVER>>> " + s ); 112 output.flush(); 113 display.append( "\nSERVER>>>" + s ); 81 display.setCaretPosition( 82 display.getText().length() );

1. Constructor 1.1 GUI components 1// Fig. 21.3: Server.java 2// Set up a Server that will receive a connection 3// from a client, send a string to the client, 4// and close the connection. 5import java.io.*; 6import java.net.*; 7import java.awt.*; 8import java.awt.event.*; 9import javax.swing.*; 10 11public class Server extends JFrame { 12 private JTextField enter; 13 private JTextArea display; 14 ObjectOutputStream output; 15 ObjectInputStream input; public Server() 18 { 19 super( "Server" ); Container c = getContentPane(); enter = new JTextField(); 24 enter.setEnabled( false );

1.2 Event handler 1.3 GUI 2. Method runServer 2.1 ServerSocket display = new JTextArea(); 36 c.add( new JScrollPane( display ), 37 BorderLayout.CENTER ); setSize( 300, 150 ); 40 show(); 41 } public void runServer() 44 { 45 ServerSocket server; 46 Socket connection; 47 int counter = 1; try { 50 // Step 1: Create a ServerSocket server = new ServerSocket( 5000, 100 ); enter.addActionListener( 26 new ActionListener() { 27 public void actionPerformed( ActionEvent e ) 28 { sendData( e.getActionCommand() ); 30 } 31 } 32 ); 33 c.add( enter, BorderLayout.NORTH ); The event handlers calls method sendData, using text in JTextField as argument. Register port 5000, server will allow 100 clients to wait in queue.

2.2 accept 2.3 getHostName 2.4 Get streams 2.5 writeObject 2.6 Loop 67 connection.getInputStream() ); 68 display.append( "\nGot I/O streams\n" ); // Step 4: Process connection. 71 String message = 72 "SERVER>>> Connection successful"; 73 output.writeObject( message ); 74 output.flush(); 75 enter.setEnabled( true ); do { 78 try { 79 message = (String) input.readObject(); 80 display.append( "\n" + message ); 81 display.setCaretPosition( 82 display.getText().length() ); 83 } while ( true ) { 54 // Step 2: Wait for a connection. 55 display.setText( "Waiting for connection\n" ); connection = server.accept(); display.append( "Connection " + counter + 59 " received from: " connection.getInetAddress().getHostName() ); // Step 3: Get input and output streams output = new ObjectOutputStream( 64 connection.getOutputStream() ); 65 output.flush(); 66 input = new ObjectInputStream( Infinite loop to wait for connections from clients. Wait for connection ( server.accept() waits indefinitely). Display host location. Set up I/O streams, flush buffer (sends stream data). Send confirmation message. Loop to get input. Set cursor to end of text.

2.6 Loop 2.7 close 3. Method sendData 3.1 writeObject 3.2 flush 100 catch ( EOFException eof ) { 101 System.out.println( "Client terminated connection" ); 102 } 103 catch ( IOException io ) { 104 io.printStackTrace(); 105 } 106 } private void sendData( String s ) 109 { 110 try { output.writeObject( "SERVER>>> " + s ); 112 output.flush(); 113 display.append( "\nSERVER>>>" + s ); 114 } 84 catch ( ClassNotFoundException cnfex ) { 85 display.append( 86 "\nUnknown object type received" ); 87 } } while ( !message.equals( "CLIENT>>> TERMINATE" ) ); // Step 5: Close connection. 91 display.append( "\nUser terminated connection" ); 92 enter.setEnabled( false ); output.close(); 94 input.close(); 95 connection.close(); counter; 98 } 99 } Loop until TERMINATE string sent. Close connection and I/O streams. Send String object to client. Flush buffer to ensure it is sent, and update server's display.

4. main app.runServer(); 135 } 136} 115 catch ( IOException cnfex ) { 116 display.append( 117 "\nError writing object" ); 118 } 119 } public static void main( String args[] ) 122 { 123 Server app = new Server(); app.addWindowListener( 126 new WindowAdapter() { 127 public void windowClosing( WindowEvent e ) 128 { 129 System.exit( 0 ); 130 } 131 } 132 );

Client/Server Interaction with Stream Socket Connections Client –Similar to server –Creates same GUI –Loops to wait for input Sends output through event handler and sendData

Client/Server Interaction with Stream Socket Connections –Create Socket with two arguments Internet address of server and port number –static method getByName (Class InetAddress ) Returns InetAddress object Takes String Could have taken "localhost" or called static method getLocalHost –Create I/O objects as before Output of server is input of client 50 client = new Socket( 51 InetAddress.getByName( " " ), 5000 );

1. Constructor 1.1 GUI 1// Fig. 21.4: Client.java 2// Set up a Client that will read information sent 3// from a Server and display the information. 4import java.io.*; 5import java.net.*; 6import java.awt.*; 7import java.awt.event.*; 8import javax.swing.*; 9 10public class Client extends JFrame { 11 private JTextField enter; 12 private JTextArea display; 13 ObjectOutputStream output; 14 ObjectInputStream input; 15 String message = ""; public Client() 18 { 19 super( "Client" ); Container c = getContentPane(); enter = new JTextField(); 24 enter.setEnabled( false );

1.2 Event handler 1.3 GUI 2. Method runClient 2.1 Socket display = new JTextArea(); 36 c.add( new JScrollPane( display ), 37 BorderLayout.CENTER ); setSize( 300, 150 ); 40 show(); 41 } public void runClient() 44 { 45 Socket client; try { 48 // Step 1: Create a Socket to make connection. 49 display.setText( "Attempting connection\n" ); 50 client = new Socket( 51 InetAddress.getByName( " " ), 5000 ); enter.addActionListener( 26 new ActionListener() { 27 public void actionPerformed( ActionEvent e ) 28 { sendData( e.getActionCommand() ); 30 } 31 } 32 ); 33 c.add( enter, BorderLayout.NORTH ); Client gets text from JTextField and calls sendData. Create Socket to server, make connection.

2.2 I/O streams 2.3 flush 2.4 Loop 67 // Step 3: Process connection. 68 enter.setEnabled( true ); do { 71 try { 72 message = (String) input.readObject(); 73 display.append( "\n" + message ); 74 display.setCaretPosition( 75 display.getText().length() ); 76 } 77 catch ( ClassNotFoundException cnfex ) { 78 display.append( 79 "\nUnknown object type received" ); 80 } 81 } while ( !message.equals( "SERVER>>> TERMINATE" ) ); display.append( "Connected to: " + 57 client.getInetAddress().getHostName() ); // Step 2: Get the input and output streams. 60 output = new ObjectOutputStream( 61 client.getOutputStream() ); output.flush(); 63 input = new ObjectInputStream( 64 client.getInputStream() ); 65 display.append( "\nGot I/O streams\n" ); 66 Code similar to server. Create I/O objects, flush buffer, loop to wait for and process input.

2.5 close 3. Method sendData 100 message = s; 101 output.writeObject( "CLIENT>>> " + s ); 102 output.flush(); 103 display.append( "\nCLIENT>>>" + s ); 104 } 105 catch ( IOException cnfex ) { 106 display.append( 107 "\nError writing object" ); 108 } 109 } // Step 4: Close connection. 84 display.append( "Closing connection.\n" ); 85 input.close(); 86 output.close(); 87 client.close(); 88 } 89 catch ( EOFException eof ) { 90 System.out.println( "Server terminated connection" ); 91 } 92 catch ( IOException e ) { 93 e.printStackTrace(); 94 } 95 } private void sendData( String s ) 98 { 99 try {

4. main Program Output 111 public static void main( String args[] ) 112 { 113 Client app = new Client(); app.addWindowListener( 116 new WindowAdapter() { 117 public void windowClosing( WindowEvent e ) 118 { 119 System.exit( 0 ); 120 } 121 } 122 ); app.runClient(); 125 } 126} 127

Program Output

Connectionless Client/Server Interaction with Datagrams Connection-oriented interaction –Like phone call Have connection to other end Connection maintained for duration of call, even if not talking Connectionless interaction –Like sending postal mail –Use datagrams, packets of data –If large packet, break into smaller pieces Send separately May arrive out of order or not arrive at all Duplicates may arrive

Connectionless Client/Server Interaction with Datagrams –DatagramSocket( port ) Binds server to port –DatagramPacket( byteArray, byteArray.length ) Create DatagramPacket to store received packet byteArray stores data –Method receive( packetToStore ) Blocks until packet arrives, stores in packetToStore 27 socket = new DatagramSocket( 5000 ); 40 byte data[] = new byte[ 100 ]; 41 receivePacket = 42 new DatagramPacket( data, data.length ); 45 socket.receive( receivePacket );

Connectionless Client/Server Interaction with Datagrams –getAddress - returns InetAddress –getPort, getLength - return integers –getData - returns byte array Used in String constructor to create string 48 display.append( "\nPacket received:" + 49 "\nFrom host: " + receivePacket.getAddress() + 50 "\nHost port: " + receivePacket.getPort() + 51 "\nLength: " + receivePacket.getLength() + 52 "\nContaining:\n\t" + 53 new String( receivePacket.getData(), 0, 54 receivePacket.getLength() ) );

Connectionless Client/Server Interaction with Datagrams –Echo packet back to client DatagramPacket( byteArray, length, InetAddress, port ) Method send( packetToSend ) 58 sendPacket = 59 new DatagramPacket( receivePacket.getData(), 60 receivePacket.getLength(), 62 receivePacket.getPort() ); 63 socket.send( sendPacket ); 61 receivePacket.getAddress(),

1. Declarations 1.1 DatagramSocket 1// Fig. 21.5: Server.java 2// Set up a Server that will receive packets from a 3// client and send packets to a client. 4import java.io.*; 5import java.net.*; 6import java.awt.*; 7import java.awt.event.*; 8import javax.swing.*; 9 10public class Server extends JFrame { 11 private JTextArea display; private DatagramPacket sendPacket, receivePacket; 14 private DatagramSocket socket; public Server() 17 { 18 super( "Server" ); display = new JTextArea(); 21 getContentPane().add( new JScrollPane( display), 22 BorderLayout.CENTER ); 23 setSize( 400, 300 ); 24 show(); try { 27 socket = new DatagramSocket( 5000 ); 28 } Create new DatagramSocket, binds server to port.

2. Method waitForPackets 2.1 receivePacket 2.2 receive 2.3 Process packet 2.4 Echo packet public void waitForPackets() 36 { while ( true ) { 38 try { 39 // set up packet 40 byte data[] = new byte[ 100 ]; 41 receivePacket = new DatagramPacket( data, data.length ); // wait for packet 45 socket.receive( receivePacket ); // process packet 48 display.append( "\nPacket received:" + 49 "\nFrom host: " + receivePacket.getAddress() + 50 "\nHost port: " + receivePacket.getPort() + 51 "\nLength: " + receivePacket.getLength() + 52 "\nContaining:\n\t" new String( receivePacket.getData(), 0, 54 receivePacket.getLength() ) ); // echo information from packet back to client 57 display.append( "\n\nEcho data to client..."); 29 catch( SocketException se ) { 30 se.printStackTrace(); 31 System.exit( 1 ); 32 } 33 } sendPacket = 59 new DatagramPacket( receivePacket.getData(), Create new DatagramPacket to receive info. Gather and display packet data. Convert byte array to a String. Create packet back to client.Loop to wait for packets.

2.5 send 3. main 67 } 68 catch( IOException io ) { 69 display.append( io.toString() + "\n" ); 70 io.printStackTrace(); 71 } 72 } 73 } public static void main( String args[] ) 76 { 77 Server app = new Server(); app.addWindowListener( 80 new WindowAdapter() { 81 public void windowClosing( WindowEvent e ) 82 { 83 System.exit( 0 ); 84 } 85 } 86 ); app.waitForPackets(); 89 } 90} 60 receivePacket.getLength(), 61 receivePacket.getAddress(), 62 receivePacket.getPort() ); socket.send( sendPacket ); 64 display.append( "Packet sent\n" ); 65 display.setCaretPosition( 66 display.getText().length() ); Send packet back to client.

Program Output

Connectionless Client/Server Interaction with Datagrams Client –Similar to server –Has JTextField Sends packets with event handler for JTextField Convert String to byteArray –String.getBytes() –Have loop to receive echoed packets from server –Constructor needs no arguments Uses next available port Server gets client's port number as part of DatagramPacket 31 socket = new DatagramSocket();

1. Constructor 1.1 GUI 1.2 Register event handler 1// Fig. 21.6: Client.java 2// Set up a Client that will send packets to a 3// server and receive packets from a server. 4import java.io.*; 5import java.net.*; 6import java.awt.*; 7import java.awt.event.*; 8import javax.swing.*; 9 10public class Client extends JFrame implements ActionListener { 11 private JTextField enter; 12 private JTextArea display; private DatagramPacket sendPacket, receivePacket; 15 private DatagramSocket socket; public Client() 18 { 19 super( "Client" ); enter = new JTextField( "Type message here" ); 22 enter.addActionListener( this ); 23 getContentPane().add( enter, BorderLayout.NORTH ); 24 display = new JTextArea(); 25 getContentPane().add( new JScrollPane( display ), 26 BorderLayout.CENTER ); 27 setSize( 400, 300 ); 28 show(); 29

1.3 DatagramSocket 2. waitForPackets 2.1 DatagramPacket 2.2 receive 2.3 Process packet 34 se.printStackTrace(); 35 System.exit( 1 ); 36 } 37 } public void waitForPackets() 40 { while ( true ) { 42 try { 43 // set up packet 44 byte data[] = new byte[ 100 ]; 45 receivePacket = 46 new DatagramPacket( data, data.length ); // wait for packet 49 socket.receive( receivePacket ); // process packet 52 display.append( "\nPacket received:" + 53 "\nFrom host: " + receivePacket.getAddress() + 54 "\nHost port: " + receivePacket.getPort() + 55 "\nLength: " + receivePacket.getLength() + 56 "\nContaining:\n\t" + 57 new String( receivePacket.getData(), 0, 58 receivePacket.getLength() ) ); 30 try { socket = new DatagramSocket(); 32 } 33 catch( SocketException se ) { No argument constructor.Similar to server, loop to receive echoed packets.

3. actionPerformed 3.1 Create packet 3.2 send 67 } public void actionPerformed( ActionEvent e ) 70 { 71 try { 72 display.append( "\nSending packet containing: " + 73 e.getActionCommand() + "\n" ); String s = e.getActionCommand(); byte data[] = s.getBytes(); sendPacket = new DatagramPacket( data, data.length, 79 InetAddress.getLocalHost(), 5000 ); 80 socket.send( sendPacket ); 81 display.append( "Packet sent\n" ); 82 display.setCaretPosition( 83 display.getText().length() ); } 86 catch ( IOException exception ) { 87 display.append( exception.toString() + "\n" ); 88 exception.printStackTrace(); 89 } 90 } 59 display.setCaretPosition( 60 display.getText().length() ); 61 } 62 catch( IOException exception ) { 63 display.append( exception.toString() + "\n" ); 64 exception.printStackTrace(); 65 } 66 } Convert String to a byte array, use to initialize DatagramPacket.

Program Output 100 System.exit( 0 ); 101 } 102 } 103 ); app.waitForPackets(); 106 } 107} public static void main( String args[] ) 93 { 94 Client app = new Client(); app.addWindowListener( 97 new WindowAdapter() { 98 public void windowClosing( WindowEvent e ) 99 {

Client/Server Tic-Tac-Toe Using a Multithreaded Server Tic-Tac-Toe –Create application allowing two clients to connect to server When each client connects –Player object created in separate thread –Manages connection –Server maintains board information Byte array represents board Determines if moves are valid –Each client has own GUI Has board information

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Server creates ServerSocket Waits for two connections, creates two Player objects –Initialize Player objects Connection to respective client, reference to server, number 50 for ( int i = 0; i < players.length; i++ ) { 52 players[ i ] = 53 new Player( server.accept(), this, i ); 54 players[ i ].start(); 29 server = new ServerSocket( 5000, 2 ); 152 connection = s; 139class Player extends Thread { 148 public Player( Socket s, TicTacToeServer t, int num ) 165 control = t; 166 number = num;

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Update server ( display ) and send client their mark (X or O) –Suspend Player X Notify Player X after Player O connects Code comes after loop to initialize both Player s 183 control.display( "Player " ( number == 0 ? 'X' : 'O' ) + " connected" ); 185 output.writeChar( mark ); 197 while ( threadSuspended ) 198 wait(); 178 public void run() 192 if ( mark == 'X' ) { 196 synchronized( this ) { 64 synchronized ( players[ 0 ] ) { 65 players[ 0 ].threadSuspended = false; 66 players[ 0 ].notify();

Client/Server Tic-Tac-Toe Using a Multithreaded Server Game begins playing –run method executes while loop –Read integer representing move from client Test if valid ( control.validMove ) If so, send message to server and client 210 while ( !done ) { 211 int location = input.readInt(); 213 if ( control.validMove( location, number ) ) { 214 control.display( "loc: " + location ); 215 output.writeUTF( "Valid move." );

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Method validMove synchronized - one move at a time –If player not currentPlayer, put in wait state When other player moves, notify 79 public synchronized boolean validMove( int loc, 80 int player ) 86 while ( player != currentPlayer ) { 88 wait();

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Checks if location occupied If not, updates byte array, currentPlayer otherPlayerMoved - informs other client of move Notify waiting client Return true (valid move) 100 notify(); // tell waiting player to continue 101 return true; 95 if ( !isOccupied( loc ) ) { 96 board[ loc ] = 97 (byte) ( currentPlayer == 0 ? 'X' : 'O' ); 98 currentPlayer = ( currentPlayer + 1 ) % 2; 99 players[ currentPlayer ].otherPlayerMoved( loc );

1. Constructor 1.1 Initialization 1.2 ServerSocket 1// Fig. 21.7: TicTacToeServer.java 2// This class maintains a game of Tic-Tac-Toe for two 3// client applets. 4import java.awt.*; 5import java.awt.event.*; 6import java.net.*; 7import java.io.*; 8import javax.swing.*; 9 10public class TicTacToeServer extends JFrame { 11 private byte board[]; 12 private boolean xMove; 13 private JTextArea output; 14 private Player players[]; 15 private ServerSocket server; 16 private int currentPlayer; public TicTacToeServer() 19 { 20 super( "Tic-Tac-Toe Server" ); board = new byte[ 9 ]; 23 xMove = true; 24 players = new Player[ 2 ]; 25 currentPlayer = 0; // set up ServerSocket 28 try { server = new ServerSocket( 5000, 2 ); 30 } Server creates ServerSocket to get connections. Use nine element byte array to represent board. Create Player array.

1.3 GUI 2. Method execute 2.1 Initialize players 34 catch( IOException e ) { 35 e.printStackTrace(); 36 System.exit( 1 ); 37 } output = new JTextArea(); 40 getContentPane().add( output, BorderLayout.CENTER ); 41 output.setText( "Server awaiting connections\n" ); setSize( 300, 300 ); 44 show(); 45 } // wait for two connections so game can be played 48 public void execute() 49 { 50 for ( int i = 0; i < players.length; i++ ) { 51 try { 52 players[ i ] = new Player( server.accept(), this, i ); 54 players[ i ].start(); 55 } 56 catch( IOException e ) { 57 e.printStackTrace(); 58 System.exit( 1 ); 59 } 60 } Initialize Player objects with client connection. Player X begins in wait state.

2.2 notify player X 3. Method display 4. Method validMove ( synchronized ) 67 } } public void display( String s ) 72 { 73 output.append( s + "\n" ); 74 } // Determine if a move is valid. 77 // This method is synchronized because only one move can be 78 // made at a time. 79 public synchronized boolean validMove( int loc, 80 int player ) 81 { 82 boolean moveDone = false; while ( player != currentPlayer ) { 87 try { 88 wait(); 89 } // Player X is suspended until Player O connects. 63 // Resume player X now. 64 synchronized ( players[ 0 ] ) { 65 players[ 0 ].threadSuspended = false; players[ 0 ].notify(); Notify player X to resume execution. Allow only one move at a time.If player is not the current player, send to wait state.

4.1 Update information 5. isOccupied 6. gameOver 100 notify(); // tell waiting player to continue 101 return true; 102 } 103 else 104 return false; 105 } public boolean isOccupied( int loc ) 108 { 109 if ( board[ loc ] == 'X' || board [ loc ] == 'O' ) 110 return true; 111 else 112 return false; 113 } public boolean gameOver() 116 { 117 // Place code here to test for a winner of the game 118 return false; 119 } 90 catch( InterruptedException e ) { 91 e.printStackTrace(); 92 } 93 } if ( !isOccupied( loc ) ) { 96 board[ loc ] = 97 (byte) ( currentPlayer == 0 ? 'X' : 'O' ); 98 currentPlayer = ( currentPlayer + 1 ) % 2; 99 players[ currentPlayer ].otherPlayerMoved( loc ); If location unoccupied, update current player, inform other player of move, board, and notify waiting players.

7. main 8. Class Player 133 game.execute(); 134 } 135} // Player class to manage each Player as a thread 139class Player extends Thread { 140 private Socket connection; 141 private DataInputStream input; 142 private DataOutputStream output; 143 private TicTacToeServer control; 144 private int number; 145 private char mark; 146 protected boolean threadSuspended = true; public static void main( String args[] ) 122 { 123 TicTacToeServer game = new TicTacToeServer(); game.addWindowListener( new WindowAdapter() { 126 public void windowClosing( WindowEvent e ) 127 { 128 System.exit( 0 ); 129 } 130 } 131 ); 132

8.1 Constructor 8.2 I/O streams 8.3 otherPlayerMoved 165 control = t; 166 number = num; 167 } public void otherPlayerMoved( int loc ) 170 { 171 try { output.writeUTF( "Opponent moved" ); 173 output.writeInt( loc ); 174 } 175 catch ( IOException e ) { e.printStackTrace(); } 176 } public Player( Socket s, TicTacToeServer t, int num ) 149 { 150 mark = ( num == 0 ? 'X' : 'O' ); connection = s; try { 155 input = new DataInputStream( 156 connection.getInputStream() ); 157 output = new DataOutputStream( 158 connection.getOutputStream() ); 159 } 160 catch( IOException e ) { 161 e.printStackTrace(); 162 System.exit( 1 ); 163 } 164 Initialize with client connection, reference to server object, and player number. Inform Player of other's move.

8.4 run Inform server Send mark Player X waits 197 while ( threadSuspended ) 198 wait(); 199 } 200 } 201 catch ( InterruptedException e ) { 202 e.printStackTrace(); 203 } output.writeUTF( 206 "Other player connected. Your move." ); 207 } public void run() 179 { 180 boolean done = false; try { control.display( "Player " ( number == 0 ? 'X' : 'O' ) + " connected" ); 185 output.writeChar( mark ); 186 output.writeUTF( "Player " ( number == 0 ? "X connected\n" : 188 "O connected, please wait\n" ) ); // wait for another player to arrive 192 if ( mark == 'X' ) { 193 output.writeUTF( "Waiting for another player" ); try { synchronized( this ) { Server displays connected client. Mark (X or O) sent to client. Player X waits (so Player O can connect). Once Player O connects, X can move.

8.5 Loop for input 8.6 validMove 227 e.printStackTrace(); 228 System.exit( 1 ); 229 } 230 } 231} 209 // Play game 210 while ( !done ) { 211 int location = input.readInt(); if ( control.validMove( location, number ) ) { 214 control.display( "loc: " + location ); 215 output.writeUTF( "Valid move." ); 216 } 217 else 218 output.writeUTF( "Invalid move, try again" ); if ( control.gameOver() ) 221 done = true; 222 } connection.close(); 225 } 226 catch( IOException e ) { Loop and get input. Check validity, and inform server and client.

Program Output

Client/Server Tic-Tac-Toe Using a Multithreaded Server Client –Creates GUI Uses nine Square objects (extend JPanel ) –start method Connects to server Gets I/O streams

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Implements interface Runnable, so separate thread can execute read input Executes run method, which loops and reads input 85 outputThread = new Thread( this ); 86 outputThread.start(); 11public class TicTacToeClient extends JApplet 12 implements Runnable {

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Method run handles input Sets player's mark Loops, gets input, calls processMessage 107 while ( true ) { 109 String s = input.readUTF(); 110 processMessage( s ); 114 } 94 public void run() 95 { 98 myMark = input.readChar();

Client/Server Tic-Tac-Toe Using a Multithreaded Server –Method processMessage Perform actions depending on String received –Listen for MouseEvent s If Square clicked, setCurrentSquare 119 public void processMessage( String s ) 121 if ( s.equals( "Valid move." ) ) { 126 else if ( s.equals( "Invalid move, try again" ) ) { 130 else if ( s.equals( "Opponent moved" ) ) { display.append( "Valid move, please wait.\n" ); 123 currentSquare.setMark( myMark ); 124 currentSquare.repaint(); 125 }

1. implements Runnable 1.1 Declarations 1.2 GUI 1// Fig. 21.8: TicTacToeClient.java 2// Client for the TicTacToe program 3import java.awt.*; 4import java.awt.event.*; 5import java.net.*; 6import java.io.*; 7import javax.swing.*; 8 9// Client class to let a user play Tic-Tac-Toe with 10// another user across a network. 11public class TicTacToeClient extends JApplet 12 implements Runnable { 13 private JTextField id; 14 private JTextArea display; 15 private JPanel boardPanel, panel2; 16 private Square board[][], currentSquare; 17 private Socket connection; 18 private DataInputStream input; 19 private DataOutputStream output; 20 private Thread outputThread; 21 private char myMark; 22 private boolean myTurn; // Set up user-interface and board 25 public void init() 26 { 27 display = new JTextArea( 4, 30 ); 28 display.setEditable( false ); 29 getContentPane().add( new JScrollPane( display ), 30 BorderLayout.SOUTH ); Allows applet to create a thread, used to get input.

1.3 GUI 1.4 Event handlers 34 boardPanel.setLayout( layout ); board = new Square[ 3 ][ 3 ]; // When creating a Square, the location argument to the 40 // constructor is a value from 0 to 8 indicating the 41 // position of the Square on the board. Values 0, 1, 42 // and 2 are the first row, values 3, 4, and 5 are the 43 // second row. Values 6, 7, and 8 are the third row. 44 for ( int row = 0; row < board.length; row++ ) 45 { 46 for ( int col = 0; 47 col < board[ row ].length; col++ ) { 48 board[ row ][ col ] = 49 new Square( ' ', row * 3 + col ); board[ row ][ col ].addMouseListener( 51 new SquareListener( 52 this, board[ row ][ col ] ) ); boardPanel.add( board[ row ][ col ] ); 55 } 56 } id = new JTextField(); 59 id.setEditable( false ); boardPanel = new JPanel(); 33 GridLayout layout = new GridLayout( 3, 3, 0, 0 ); Register event handlers for each Square.

2. start 2.1 Socket 2.2 Thread // Make connection to server and get associated streams. 69 // Start separate thread to allow this applet to 70 // continually update its output in text area display. 71 public void start() 72 { 73 try { 74 connection = new Socket( InetAddress.getByName( " " ), 5000 ); 76 input = new DataInputStream( 77 connection.getInputStream() ); 78 output = new DataOutputStream( 79 connection.getOutputStream() ); 80 } 81 catch ( IOException e ) { 82 e.printStackTrace(); 83 } outputThread = new Thread( this ); 86 outputThread.start(); 87 } getContentPane().add( id, BorderLayout.NORTH ); panel2 = new JPanel(); 64 panel2.add( boardPanel, BorderLayout.CENTER ); 65 getContentPane().add( panel2, BorderLayout.CENTER ); 66 } Get connection to server.Create new thread, which executes method run.

3. run 3.1 Get mark 3.2 Loop for input 100 myTurn = ( myMark == 'X' ? true : false ); 101 } 102 catch ( IOException e ) { 103 e.printStackTrace(); 104 } // Receive messages sent to client 107 while ( true ) { 108 try { 109 String s = input.readUTF(); 110 processMessage( s ); 111 } 112 catch ( IOException e ) { 113 e.printStackTrace(); 114 } 115 } 116 } // Control thread that allows continuous update of the 93 // text area display. 94 public void run() 95 { 96 // First get player's mark (X or O) 97 try { myMark = input.readChar(); 99 id.setText( "You are player \"" + myMark + "\"" ); Get player's mark (first data sent) then loop for more input.

4. processMessage 4.1 setMark board[ loc / 3 ][ loc % 3 ].setMark( 135 ( myMark == 'X' ? 'O' : 'X' ) ); 136 board[ loc / 3 ][ loc % 3 ].repaint(); display.append( 139 "Opponent moved. Your turn.\n" ); 140 myTurn = true; 141 } catch ( IOException e ) { 144 e.printStackTrace(); 145 } 146 } 118 // Process messages sent to client 119 public void processMessage( String s ) 120 { 121 if ( s.equals( "Valid move." ) ) { 122 display.append( "Valid move, please wait.\n" ); currentSquare.setMark( myMark ); 124 currentSquare.repaint(); 125 } 126 else if ( s.equals( "Invalid move, try again" ) ) { 127 display.append( s + "\n" ); 128 myTurn = true; 129 } 130 else if ( s.equals( "Opponent moved" ) ) { 131 try { 132 int loc = input.readInt(); Process string. If valid move, update current square with mark. If opponent moved, update appropriate square (in board array).

5. sendClickedSquare 6. setCurrentSquare 7. Class Square public void setCurrentSquare( Square s ) 167 { 168 currentSquare = s; 169 } 170} // Maintains one square on the board 173class Square extends JPanel { 174 private char mark; 175 private int location; else 148 display.append( s + "\n" ); display.setCaretPosition( 151 display.getText().length() ); 152 } public void sendClickedSquare( int loc ) 155 { 156 if ( myTurn ) 157 try { 158 output.writeInt( loc ); 159 myTurn = false; 160 } 161 catch ( IOException ie ) { 162 ie.printStackTrace(); 163 } 164 }

7. Class Square public void paintComponent( Graphics g ) 199 { 200 super.paintComponent( g ); 201 g.drawRect( 0, 0, 29, 29 ); 202 g.drawString( String.valueOf( mark ), 11, 20 ); 203 } 204} 177 public Square( char m, int loc) 178 { 179 mark = m; 180 location = loc; 181 setSize ( 30, 30 ); setVisible(true); 184 } public Dimension getPreferredSize() { 187 return ( new Dimension( 30, 30 ) ); 188 } public Dimension getMinimumSize() { 191 return ( getPreferredSize() ); 192 } public void setMark( char c ) { mark = c; } public int getSquareLocation() { return location; }

8. Event handler class SquareListener extends MouseAdapter { 207 private TicTacToeClient applet; 208 private Square square; public SquareListener( TicTacToeClient t, Square s ) 211 { 212 applet = t; 213 square = s; 214 } public void mouseReleased( MouseEvent e ) 217 { 218 applet.setCurrentSquare( square ); 219 applet.sendClickedSquare( square.getSquareLocation() ); 220 } 221}

Program Output

Program Output

Security and the Network Security –Many Web browsers prevent file processing by applets (by default) Malicious applets could be a security risk Applets can usually only talk with the machine that downloaded it and its server Trusted source –Browsers can determine if applet came from trusted source –If so, can be given more access