We present a tutorial on socket programming in Java. This tutorial illustrates several examples on the two types of socket APIs: connectionless datagram sockets and connection-oriented stream-mode sockets.

Sockets allow communication between two different processes on the same or different machines. A socket is bound to a port number so that the transport layer can identify the application that data is destined to be sent to.

In this section we will answer the most frequently asked questions about programming sockets in Java. Then we will show some examples of how to write client and server applications.

2.7.1 Socket Programming with TCP Recall from Section 2.1 that processes running on different machines communicate with each other by sending messages into sockets. We said that each process was analogous to a house and the process’s socket is analogous to a door.

Sockets are a means of using IP to communicate between machines, so sockets are one major feature that allows Java to interoperate with legacy systems by simply talking to existing servers using their pre-defined protocol.

To connect to a different host, you must create a new Socket object. Sending and receiving data is accomplished with output and input streams. There are methods to get an input stream for a socket and an output stream for the socket. The java.net.ServerSocket class represents a server socket. It is constructed on a particular port.

The chapter introduces the java.net package containing various classes re-quired for creating sockets and message communication using two diff erent protocols. It provides several example programs demonstrating various capabilities supported by Java for creating network applications.

This tutorial will tell you what you really need to know to start using sockets effectively in your Java code. Specifically, we'll cover: If you can describe how to use the classes in the java.net package, this tutorial is probably a little basic for you, although it might be a good refresher.

What is a Socket? A socket is a method for accomplishing inter-process communication (IPC) Allows one process to communicate with another process on the same or different machine

Open Server Socket: ServerSocket server; DataOutputStream os ; DataInputStream is; server = new ServerSocket ( PORT ); 2. Wait for Client Request: Socket client = server.accept(); 3. Create I/O streams for communicating to clients is = new DataInputStream ( client.getInputStream () ); os = new DataOutputStream ( client.getOutputStream () ); 4.