Servlets are a special kind of "server-side" Java application. While Java applets are special Java programs that are downloaded from a webserver and run by the web client, a servlet is a piece of Java software that is run by the server itself on behalf of the client. A servlet is a generic server extension--a Java class that can be loaded dynamically to expand the functionality of a server. Servlets most are commonly used with web servers, where they can take the place of CGI scripts.

Servlets are most commonly known as replacements for the older (but still current) technique of CGI scripts, and have advantages over CGIs, the most obvious being that since Java is a fully functional programming language while a CGI is created using a basic scripting language like Perl, a Java servlet has the full power of an application program, and can be used...