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CS 491, 591 Networking in Java Summer 2007. 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

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establishing a simple server using stream sockets
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
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 sockets1
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 sockets2
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 sockets3
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
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 connections1

60 connection.getInetAddress().getHostName() );

63 output = new ObjectOutputStream(

64 connection.getOutputStream() );

65 output.flush();

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
client server interaction with stream socket connections2

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() );

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
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.

5 import java.io.*;

6 import java.net.*;

7 import java.awt.*;

8 import java.awt.event.*;

9 import javax.swing.*;

10

11 public class Server extends JFrame {

12 private JTextField enter;

13 private JTextArea display;

14 ObjectOutputStream output;

15 ObjectInputStream input;

16

17 public Server()

18 {

19 super( "Server" );

20

21 Container c = getContentPane();

22

23 enter = new JTextField();

24 enter.setEnabled( false );

1. Constructor

1.1 GUI components

1 2 event handler 1 3 gui 2 method runserver 2 1 serversocket

34

35 display = new JTextArea();

36 c.add( new JScrollPane( display ),

The event handlers calls method sendData, using text in JTextField as argument.

37 BorderLayout.CENTER );

38

39 setSize( 300, 150 );

40 show();

41 }

Register port 5000, server will allow 100 clients to wait in queue.

42

43 public void runServer()

44 {

45 ServerSocket server;

46 Socket connection;

47 int counter = 1;

48

49 try {

50 // Step 1: Create a ServerSocket.

51 server = new ServerSocket( 5000, 100 );

52

25 enter.addActionListener(

26 new ActionListener() {

27 public void actionPerformed( ActionEvent e )

28 {

29 sendData( e.getActionCommand() );

30 }

31 }

32 );

33 c.add( enter, BorderLayout.NORTH );

1.2 Event handler

1.3 GUI

2. Method runServer

2.1 ServerSocket

2 2 accept 2 3 gethostname 2 4 get streams 2 5 writeobject 2 6 loop

67 connection.getInputStream() );

Infinite loop to wait for connections from clients.

68 display.append( "\nGot I/O streams\n" );

69

Wait for connection (server.accept() waits indefinitely).

70 // Step 4: Process connection.

71 String message =

Display host location.

72 "SERVER>>> Connection successful";

Set up I/O streams, flush buffer (sends stream data). Send confirmation message.

73 output.writeObject( message );

74 output.flush();

Loop to get input. Set cursor to end of text.

75 enter.setEnabled( true );

76

77 do {

78 try {

79 message = (String) input.readObject();

80 display.append( "\n" + message );

81 display.setCaretPosition(

82 display.getText().length() );

83 }

53 while ( true ) {

54 // Step 2: Wait for a connection.

55 display.setText( "Waiting for connection\n" );

56 connection = server.accept();

57

58 display.append( "Connection " + counter +

59 " received from: " +

60 connection.getInetAddress().getHostName() );

61

62 // Step 3: Get input and output streams.

63 output = new ObjectOutputStream(

64 connection.getOutputStream() );

65 output.flush();

66 input = new ObjectInputStream(

2.2 accept

2.3 getHostName

2.4 Get streams

2.5 writeObject

2.6 Loop

2 6 loop 2 7 close 3 method senddata 3 1 writeobject 3 2 flush

100 catch ( EOFException eof ) {

Loop until TERMINATE string sent.

101 System.out.println( "Client terminated connection" );

102 }

103 catch ( IOException io ) {

Close connection and I/O streams.

104 io.printStackTrace();

105 }

106 }

107

Send String object to client. Flush buffer to ensure it is sent, and update server's display.

108 private void sendData( String s )

109 {

110 try {

111 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 }

88 } while ( !message.equals( "CLIENT>>> TERMINATE" ) );

89

90 // Step 5: Close connection.

91 display.append( "\nUser terminated connection" );

92 enter.setEnabled( false );

93 output.close();

94 input.close();

95 connection.close();

96

97 ++counter;

98 }

99 }

2.6 Loop

2.7 close

3. Method sendData

3.1 writeObject

3.2 flush

4 main

133

134 app.runServer();

135 }

136 }

115 catch ( IOException cnfex ) {

116 display.append(

117 "\nError writing object" );

118 }

119 }

120

121 public static void main( String args[] )

122 {

123 Server app = new Server();

124

125 app.addWindowListener(

126 new WindowAdapter() {

127 public void windowClosing( WindowEvent e )

128 {

129 System.exit( 0 );

130 }

131 }

132 );

4. main

client server interaction with stream socket connections3
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 connections4

50 client = new Socket(

51 InetAddress.getByName( "127.0.0.1" ), 5000 );

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
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.

4 import java.io.*;

5 import java.net.*;

6 import java.awt.*;

7 import java.awt.event.*;

8 import javax.swing.*;

9

10 public class Client extends JFrame {

11 private JTextField enter;

12 private JTextArea display;

13 ObjectOutputStream output;

14 ObjectInputStream input;

15 String message = "";

16

17 public Client()

18 {

19 super( "Client" );

20

21 Container c = getContentPane();

22

23 enter = new JTextField();

24 enter.setEnabled( false );

1. Constructor

1.1 GUI

1 2 event handler 1 3 gui 2 method runclient 2 1 socket

34

35 display = new JTextArea();

36 c.add( new JScrollPane( display ),

Client gets text from JTextField and calls sendData.

37 BorderLayout.CENTER );

38

39 setSize( 300, 150 );

40 show();

Create Socket to server, make connection.

41 }

42

43 public void runClient()

44 {

45 Socket client;

46

47 try {

48 // Step 1: Create a Socket to make connection.

49 display.setText( "Attempting connection\n" );

50 client = new Socket(

51 InetAddress.getByName( "127.0.0.1" ), 5000 );

52

53

54

55

25 enter.addActionListener(

26 new ActionListener() {

27 public void actionPerformed( ActionEvent e )

28 {

29 sendData( e.getActionCommand() );

30 }

31 }

32 );

33 c.add( enter, BorderLayout.NORTH );

1.2 Event handler

1.3 GUI

2. Method runClient

2.1 Socket

2 2 i o streams 2 3 flush 2 4 loop

67 // Step 3: Process connection.

68 enter.setEnabled( true );

69

70 do {

71 try {

Code similar to server. Create I/O objects, flush buffer, loop to wait for and process input.

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" ) );

82

56 display.append( "Connected to: " +

57 client.getInetAddress().getHostName() );

58

59 // Step 2: Get the input and output streams.

60 output = new ObjectOutputStream(

61 client.getOutputStream() );

62 output.flush();

63 input = new ObjectInputStream(

64 client.getInputStream() );

65 display.append( "\nGot I/O streams\n" );

66

2.2 I/O streams

2.3 flush

2.4 Loop

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 }

110

83 // 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 }

96

97 private void sendData( String s )

98 {

99 try {

2.5 close

3. Method sendData

4 main program output

111 public static void main( String args[] )

112 {

113 Client app = new Client();

114

115 app.addWindowListener(

116 new WindowAdapter() {

117 public void windowClosing( WindowEvent e )

118 {

119 System.exit( 0 );

120 }

121 }

122 );

123

124 app.runClient();

125 }

126 }

127

4. main

Program Output

program output
Program

Output

connectionless client server interaction with datagrams
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 datagrams1

40 byte data[] = new byte[ 100 ];

41 receivePacket =

42 new DatagramPacket( data, data.length );

45 socket.receive( receivePacket );

27 socket = new DatagramSocket( 5000 );

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
connectionless client server interaction with datagrams2

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
  • getAddress - returns InetAddress
  • getPort, getLength - return integers
  • getData - returns byte array
    • Used in String constructor to create string
connectionless client server interaction with datagrams3

58 sendPacket =

59 new DatagramPacket( receivePacket.getData(),

60 receivePacket.getLength(),

61 receivePacket.getAddress(),

62 receivePacket.getPort() );

63 socket.send( sendPacket );

Connectionless Client/Server Interaction with Datagrams
  • Echo packet back to client
    • DatagramPacket( byteArray, length, InetAddress, port )
    • Method send( packetToSend )
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.

4 import java.io.*;

5 import java.net.*;

6 import java.awt.*;

7 import java.awt.event.*;

8 import javax.swing.*;

9

Create new DatagramSocket, binds server to port.

10 public class Server extends JFrame {

11 private JTextArea display;

12

13 private DatagramPacket sendPacket, receivePacket;

14 private DatagramSocket socket;

15

16 public Server()

17 {

18 super( "Server" );

19

20 display = new JTextArea();

21 getContentPane().add( new JScrollPane( display),

22 BorderLayout.CENTER );

23 setSize( 400, 300 );

24 show();

25

26 try {

27 socket = new DatagramSocket( 5000 );

28 }

1. Declarations

1.1 DatagramSocket

2 method waitforpackets 2 1 receivepacket 2 2 receive 2 3 process packet 2 4 echo packet

34

35 public void waitForPackets()

Loop to wait for packets.

36 {

Create new DatagramPacket to receive info.

37 while ( true ) {

38 try {

39 // set up packet

40 byte data[] = new byte[ 100 ];

Gather and display packet data. Convert byte array to a String.

41 receivePacket =

42 new DatagramPacket( data, data.length );

43

Create packet back to client.

44 // wait for packet

45 socket.receive( receivePacket );

46

47 // 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" +

53 new String( receivePacket.getData(), 0,

54 receivePacket.getLength() ) );

55

56 // echo information from packet back to client

57 display.append( "\n\nEcho data to client...");

58 sendPacket =

59 new DatagramPacket( receivePacket.getData(),

29 catch( SocketException se ) {

30 se.printStackTrace();

31 System.exit( 1 );

32 }

33 }

2. Method waitForPackets

2.1 receivePacket

2.2 receive

2.3 Process packet

2.4 Echo packet

2 5 send 3 main

67 }

68 catch( IOException io ) {

Send packet back to client.

69 display.append( io.toString() + "\n" );

70 io.printStackTrace();

71 }

72 }

73 }

74

75 public static void main( String args[] )

76 {

77 Server app = new Server();

78

79 app.addWindowListener(

80 new WindowAdapter() {

81 public void windowClosing( WindowEvent e )

82 {

83 System.exit( 0 );

84 }

85 }

86 );

87

88 app.waitForPackets();

89 }

90 }

60 receivePacket.getLength(),

61 receivePacket.getAddress(),

62 receivePacket.getPort() );

63 socket.send( sendPacket );

64 display.append( "Packet sent\n" );

65 display.setCaretPosition(

66 display.getText().length() );

2.5 send

3. main

connectionless client server interaction with datagrams4

31 socket = new DatagramSocket();

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
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.

4 import java.io.*;

5 import java.net.*;

6 import java.awt.*;

7 import java.awt.event.*;

8 import javax.swing.*;

9

10 public class Client extends JFrame implements ActionListener {

11 private JTextField enter;

12 private JTextArea display;

13

14 private DatagramPacket sendPacket, receivePacket;

15 private DatagramSocket socket;

16

17 public Client()

18 {

19 super( "Client" );

20

21 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. Constructor

1.1 GUI

1.2 Register event handler

1 3 datagramsocket 2 waitforpackets 2 1 datagrampacket 2 2 receive 2 3 process packet

34 se.printStackTrace();

No argument constructor.

35 System.exit( 1 );

36 }

37 }

Similar to server, loop to receive echoed packets.

38

39 public void waitForPackets()

40 {

41 while ( true ) {

42 try {

43 // set up packet

44 byte data[] = new byte[ 100 ];

45 receivePacket =

46 new DatagramPacket( data, data.length );

47

48 // wait for packet

49 socket.receive( receivePacket );

50

51 // 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 {

31 socket = new DatagramSocket();

32 }

33 catch( SocketException se ) {

1.3 DatagramSocket

2. waitForPackets

2.1 DatagramPacket

2.2 receive

2.3 Process packet

3 actionperformed 3 1 create packet 3 2 send

67 }

68

69 public void actionPerformed( ActionEvent e )

70 {

71 try {

Convert String to a byte array, use to initialize DatagramPacket.

72 display.append( "\nSending packet containing: " +

73 e.getActionCommand() + "\n" );

74

75 String s = e.getActionCommand();

76 byte data[] = s.getBytes();

77

78 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() );

84

85 }

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 }

3. actionPerformed

3.1 Create packet

3.2 send

program output2

100 System.exit( 0 );

101 }

102 }

103 );

104

105 app.waitForPackets();

106 }

107 }

91

92 public static void main( String args[] )

93 {

94 Client app = new Client();

95

96 app.addWindowListener(

97 new WindowAdapter() {

98 public void windowClosing( WindowEvent e )

99 {

Program Output