1. Sockets Sockets A socket is an object that encapsulates a TCP/IP connection There is a socket on both ends of a connection, the client side and the server side.

2. A socket has two streams, one for input and one for output. In a client/server application: the client’ output stream is connected to the server’s input stream the server’s output stream is connected to the client’s output stream Typical scenerio: Server program creates a socket at a certain port and waits until a client requests a connection Client program creates a socket and attempts to make a connection Once the connection is established the client and server communicate Client closes connection.

3. A Server Program A server application waits for the client to connect on a certain port. We choose 8888 To listen for incoming connections, use a server socket To construct a server socket, provide the port number ServerSocket server = new ServerSocket(8888); Use the accept method to wait for client connection: Socket s = server.accept(); //accept() will wait until a connection is established.. Java will notify when this happens Now can open input/output to socket: s.getInputStream provides reference to the socket’s input stream

4. Client Program Client Program Syntax to create a socket in a Java program Socket s = new Socket(hostname, portnumber); Code to connect to the HTTP port of server, java.sun.com final int HTTP_PORT = 80; Socket s= new Socket("java.sun.com",HTTP_PORT ); again, now access this sockets input and output stream InputStream in = s.getInputStream() OutputSteam out = s.getOutputSTream Client socket should close when done: s.close(); s.

5. Let’s look at a Server program which ‘echo’s all text Receives until ‘goodbye’ is received. … we’ll test it with Telnet (localhost, port=55555) netSEx5.java

6. Now, a client to go with it………………