Sockets A socket is an object that encapsulates

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.

• 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.

• 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 Server. Socket server = new Server. Socket(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. get. Input. Stream provides reference to the socket’s input stream

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 Input. Stream in = s. get. Input. Stream() Output. Steam out = s. get. Output. STream • Client socket should close when done: s. close(); s.

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) net. SEx 5. java

Now, a client to go with it………………