1. Socket Communication
Sockets provide an abstraction of two-point communication
The two sides only read/write without concern for how data is
translated (encoded) and transmitted
Socket is a pair (address, port)
address: turing.cc.gettysburg.edu,
port: 21 (ftp), 22 (ssh), 23 (telnet), 80 (http), 101 (pop mail)

2. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
client ( )
web server listen
on port 80

3. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
request web page
turing.cc…:80
client ( )
socket
:1234
web server listen
on port 80

4. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
request web page
turing.cc…:80
client ( )
socket
:1234
accept request
socket
tuing.cc…..:5789
web server listen
on port 80

5. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
client ( )
socket
tuing.cc…..:5789
socket
:1234
web server listen
on port 80

6. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
client ( )
socket
tuing.cc…..:5789
socket
:1234
request web page
turing.cc…:80
client ( )
web server listen
on port 80
socket
:1024

7. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
client ( )
socket
tuing.cc…..:5789
socket
:1234
request web page
turing.cc…:80
client ( )
web server listen
on port 80
socket
:1024
accept request
socket
tuing.cc…..:8019

8. Socket Communication web server listen on port 80
server (turing.cc.gettysburg.edu)
client ( )
socket
tuing.cc…..:5789
socket
:1234
client ( )
web server listen
on port 80
socket
tuing.cc…..:8019
socket
:1024

9. Multi-Threaded Server
client ( )
request web page
turing.cc…:80
server socket (addr : port)
turing.cc.gettysburg.edu : 80
socket (addr : port)
: 1234
socket
tuing.cc…..:5789
request web page
turing.cc…:80
client ( )
socket (addr : port)
: 1234
socket
tuing.cc…..:8019
listening thread
(wait for connect)

10. Simple Server (one client)
Open the Server Socket
ServerSocket server = new ServerSocket(5678);
Wait for Client Request
Socket connection = server.accept();
Create Streams for Communication
OutputStream os = connection.getOutputStream();
DataOutputStream output = new DataOutputStream (os);
Carry Out Communication
output.writeUTF("Hi there");
Close Communication
output.close(); os.close();
connection.close(); server.close();

11. Simple Server (one client)
public static void main(String[] args) {
// Register service on port 1234
ServerSocket server = new ServerSocket(1234);
// Wait and accept a connection
Socket connection = server.accept();
// Get a communication stream associated with the socket
OutputStream os = connection.getOutputStream();
DataOutputStream output = new DataOutputStream(os);
// Send a string!
output.writeUTF("Hi there");
// Close the connection
output.close(); os.close();
connection.close(); server.close(); }

12. Multi-Threaded Server
Open the Server Socket
ServerSocket server = new ServerSocket(5678);
Wait for Client Request
Socket connection = server.accept();
Spawn a client thread (give the connection)
Create Streams for Communication
OutputStream os = connection.getOutputStream();
DataOutputStream output = new DataOutputStream (os);
Carry Out Communication
output.writeUTF("Hi there");
Close Communication
output.close(); os.close();
connection.close(); server.close();

13. Simple Server (one client)
public static void main(String[] args) {
// Register service on port 1234
ServerSocket server = new ServerSocket(1234);
// Wait and accept a connection
while (true) {
Socket connection = server.accept();
Thread client = new ClientThread(connection); }
Code for ClientThread:
// get communication channel associated with the socket
OutputStream os = connection.getOutputStream();
DataOutputStream output = new DataOutputStream (os);
output.writeUTF("Hi there"); // communicate
os.close(); output.close(); // close resources
connection.close();

14. Simple Client MIDlet (no change)
Create a Socket Connection
SocketConnection connection =
(SocketConnection)Connector.open("socket://gbcs10:5678");
Create Streams for Communication
InputStream is = connection.openInputStream();
DataInputStream input = new DataInputStream(is);
Carry Out Communication
String data = new String (input.readUTF());
Close Communication
is.close(); input.close(); connection.close();

15. Simple Client MIDlet (no change)
try {
SocketConnection connection =
(SocketConnection) Connector.open("socket://gbcs10:1234");
InputStream is = connection.openInputStream();
DataInputStream input = new DataInputStream(is);
String data = new String (input.readUTF());
is.close(); input.close(); connection.close(); }
catch (. . .) {

16. Synchronous Multi-Threaded Chat Server
Lab Exercise
Synchronous Multi-Threaded Chat Server