Java Network Programming, Second Edition

The Socket Class

The java.net.Socket class is Java’s fundamental class for performing client-side TCP operations. Other client-oriented classes that make TCP network connections, such as URL, URLConnection, Applet, and JEditorPane, all ultimately end up invoking the methods of this class. This class itself uses native code to communicate with the local TCP stack of the host operating system. The methods of the Socket class set up and tear down connections and set as various socket options. Because TCP sockets are more or less reliable connections, the interface that the Socket class provides to the programmer is streams. The actual reading and writing of data over the socket is accomplished via the familiar stream classes.

The Constructors

The four nondeprecated public Socket constructors are simple. Each lets you specify the host and the port you want to connect to. Hosts may be specified as an InetAddress or a String. Ports are always specified as int values from to 65,535. Two of the constructors also specify the local address and local port from which data will be sent. You might need to do this when you want to select one particular network interface from which to send data on a multihomed host.

In Java 1.1 and later, the Socket class also has two protected constructors. Network clients and servers will probably never need to use these; they become important if you’re creating a subclass of Socket (perhaps to implement a new type of socket that automatically performs encryption, ...