Java Sockets under the hood

Summary Before we start coding:

• An Endpoint is a combination of Port and IP address, so every TCP connection can be identified by a pair of Endpoints
• Server waits listening to the socket (which is identified by a server local port and its IP address) for a client to make a connection request
• Client tries to rendezvous with the server’s machine and port

After this brief introduction we will introduce some classes that implements the tools which will need to make two systems or more communicating data between each other.

Let’s see a little bit under the hood:

The java.net package provides the class “Socket” which implements one side of the bidirectional connection, by the way, one of the provided constructors of this class takes as input: the remote IP address and port. The class “Socket” is called also client socket, it sits on top of a platform-dependent implementation, hiding the details of any particular system from your Java program. By using the java.net.Socket class instead of relying on native code, your Java programs can communicate over the network in a platform-independent fashion.

Additionally, java.net includes the ServerSocket class, which implements the server-side socket, which servers can use to listen for and accept connections to clients. Later on, we will see how to use the Socket and ServerSocket classes in sample code.

There are some other classes which provide other features, like connecting to a remote web server, the related classes are (URLConnection, URLEncoder), these classes are probably more appropriate than the socket classes. In fact, URLs are a relatively high-level connection to the Web and use sockets as part of the underlying implementation, in the next chapters we will see how to deal with those classes.