Lesson: All About Sockets
URLs and
URLConnections provide
a relatively high-level mechanism for
accessing resources on the Internet. Sometimes your programs require
lower-level network communication, for example, when you want to write
a client-server application.
In client-server applications, the server provides some service,
such as processing database queries or sending out current stock prices.
The client uses the service provided by the server, either displaying
database query results to the user or making stock purchase
recommendations to an investor. The communication that occurs between
the client and the server must be reliable. That is, no data can be
dropped and it must arrive on the client side in the same order in
which the server sent it.
TCP provides a reliable, point-to-point communication channel that
client-server applications on the Internet use to communicate with each
other. To communicate over TCP, a client program and a server program
establish a connection to one another. Each program binds a socket to
its end of the connection. To communicate, the client and the server
each reads from and writes to the socket bound to the connection.
A socket is one end-point of a two-way communication link between two
programs running on the network. Socket classes are used to represent the
connection between a client program and a server program. The java.net
package provides two classes--Socket and ServerSocket--that implement the
client side of the connection and the server side of the connection,
respectively.
This page contains a small example that illustrates how a client program
can read from and write to a socket.
The previous page showed an example of how to write a client program
that interacts with an existing server via a Socket object. This
page shows you how to write a program that implements the other
side of the connection--a server program.
