Java on the Server Side
As useful as applets can be,
they are just one half of the client/server equation. Not long after the
initial release of Java, it became obvious that Java would also be useful on
the server side. The result was the servlet.
A servlet is a small program that executes on the server. Just as applets
dynamically extend the functionality of a web browser, servlets dynamically
extend the functionality of a web server. Thus, with the advent of the servlet,
Java spanned both sides of the client/server connection.
Servlets are used to create
dynamically generated content that is then served to the client. For example,
an online store might use a servlet to look up the price for an item in a
database. The price information is then used to dynamically generate a web page
that is sent to the browser. Although dynamically generated content is
available through mechanisms such as CGI (Common Gateway Interface), the
servlet offers several advantages, including increased performance.
Because servlets (like all
Java programs) are compiled into bytecode and executed by the JVM, they are
highly portable. Thus, the same servlet can be used in a variety of different
server environments. The only requirements are that the server support the JVM
and a servlet container.