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

2. 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.

3. 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).

4. 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.

5. 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();

6. 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”);