Post on 21-Jan-2016
description
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
• 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.
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 );
1.2 Event handler
1.3 GUI
2. Method runServer
2.1 ServerSocket
34
35 display = new JTextArea();
36 c.add( new JScrollPane( display ),
37 BorderLayout.CENTER );
38
39 setSize( 300, 150 );
40 show();
41 }
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.
5151 server = new ServerSocket( 5000, 100 );
52
25 enter.addActionListener(
26 new ActionListener() {
27 public void actionPerformed( ActionEvent e )
28 {
2929 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" );69 70 // Step 4: Process connection.71 String message =72 "SERVER>>> Connection successful";73 output.writeObject( message );74 output.flush();75 enter.setEnabled( true );767777 do {78 try {79 message = (String) input.readObject();80 display.append( "\n" + message );81 display.setCaretPosition(82 display.getText().length() );83 }
5353 while ( true ) {54 // Step 2: Wait for a connection.55 display.setText( "Waiting for connection\n" );5656 connection = server.accept();57 58 display.append( "Connection " + counter +59 " received from: " +6060 connection.getInetAddress().getHostName() );6162 // Step 3: Get input and output streams.6363 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 flush100 catch ( EOFException eof ) {101 System.out.println( "Client terminated connection" );102 }103 catch ( IOException io ) {104 io.printStackTrace();105 }106 }107108 private void sendData( String s )109 {110 try {111111 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 }8888 } while ( !message.equals( "CLIENT>>> TERMINATE" ) );8990 // Step 5: Close connection.91 display.append( "\nUser terminated connection" );92 enter.setEnabled( false );9393 output.close();94 input.close();95 connection.close();9697 ++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
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 );
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( "127.0.0.1" ), 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.
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 );
1.2 Event handler
1.3 GUI
2. Method runClient
2.1 Socket
3435 display = new JTextArea();36 c.add( new JScrollPane( display ),37 BorderLayout.CENTER );3839 setSize( 300, 150 );40 show();41 }4243 public void runClient() 44 {45 Socket client;4647 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 );52535455
25 enter.addActionListener(26 new ActionListener() {27 public void actionPerformed( ActionEvent e )28 {2929 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 );
69
70 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" ) );
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() );
6262 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 }
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 }9697 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();
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
ProgramOutput
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.
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 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 }
Create new DatagramSocket, binds server to port.
2. Method waitForPackets
2.1 receivePacket
2.2 receive
2.3 Process packet
2.4 Echo packet
3435 public void waitForPackets()36 {3737 while ( true ) {38 try {39 // set up packet40 byte data[] = new byte[ 100 ];41 receivePacket =4242 new DatagramPacket( data, data.length );4344 // wait for packet45 socket.receive( receivePacket );46 47 // process packet48 display.append( "\nPacket received:" +49 "\nFrom host: " + receivePacket.getAddress() +50 "\nHost port: " + receivePacket.getPort() +51 "\nLength: " + receivePacket.getLength() +52 "\nContaining:\n\t" +5353 new String( receivePacket.getData(), 0,54 receivePacket.getLength() ) );5556 // echo information from packet back to client57 display.append( "\n\nEcho data to client...");
29 catch( SocketException se ) {30 se.printStackTrace();31 System.exit( 1 );32 }33 }
5858 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. main67 }68 catch( IOException io ) {69 display.append( io.toString() + "\n" );70 io.printStackTrace();71 }72 }73 }7475 public static void main( String args[] )76 {77 Server app = new Server();7879 app.addWindowListener(80 new WindowAdapter() {81 public void windowClosing( WindowEvent e )82 {83 System.exit( 0 );84 }85 }86 );8788 app.waitForPackets();89 }90 }
60 receivePacket.getLength(),
61 receivePacket.getAddress(),
62 receivePacket.getPort() );
6363 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.
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
1.3 DatagramSocket
2. waitForPackets
2.1 DatagramPacket
2.2 receive
2.3 Process packet
34 se.printStackTrace();
35 System.exit( 1 );
36 }
37 }
38
39 public void waitForPackets()
40 {
4141 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 {
3131 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 }6869 public void actionPerformed( ActionEvent e )70 {71 try {72 display.append( "\nSending packet containing: " +73 e.getActionCommand() + "\n" );7475 String s = e.getActionCommand();7676 byte data[] = s.getBytes();7778 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() );8485 }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 );
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 {