Lab 6: Introduction to Sockets (Web Programming – Part 1) Reference: Head First Java (2 nd Edition) by Kathy Sierra & Bert Bates

Connecting with the outside world Your Java program can reach out and communicate with a program on another machine. All the low-level networking details are taken care of by classes in the java.net library. One of Java’s big benefits is that sending and receiving data over a network is just I/O with a slightly different connection stream at the end of the chain. We are going to learn how to connect to the outside world by creating client and server sockets.

What is a Socket? To connect to another machine, we need a Socket connection. A Socket is an object that represents a network connection between two machines. A connection is a relationship between two machines, where two pieces of software know about each other and, most importantly, they know how to communicate with each other. To make a Socket connection, you need to know two things about the server first: 1. Who it is (IP Address). 2. Which port it’s running on (Port number).

Getting the client to work 1. Client connects to the server by establishing a Socket connection. 2. Client sends a message to the server. 3. Client gets a message from the server.

Reading from a Socket To read data from a Socket, we use a BufferedReader. 1. Make a Socket connection to the Server. Socket gameSocket = new Socket(IPaddress, PortNumber); 2. Make an InputStreamReader chained to the Socket’s low-level (connection) input stream. InputStreamReader stream = new InputStreamReader(gameSocket.getInputStream()); 3. Make the BufferedReader and read! BufferedReader = new BufferedReader(stream); String message = reader.readLine();

Writing to a Socket To write data to a Socket, we use a PrintWriter. 1. Make a Socket connection to the Server. Socket gameSocket = new Socket(IPaddress, PortNumber); 2. Make a PrintWriter chained to the Socket’s low-level (connection) output stream. PrintWriter writer = new PrintWriter(gameSocket.getInputStream()); 3. Write (print) something! writer.println(“message to send”);