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Java Servlets
A Java program that runs as part of a network service, typically an HTTP server and responds to requests from clients. The most common use for a servlet is to extend a web server by generating web content dynamically. For example, a client may need information from a database; a servlet can be written that receives the request, gets and processes the data as needed by the client and then returns the result to the client.

Applets are also written in Java but run inside the JVM of a HTML browser on the client. Servlets and applets allow the server and client to be extended in a modular way by dynamically loading code which communicates with the main program via a standard programming interface.

Servlets are more flexible than CGI scripts and, being written in Java, more portable.

Java Servlet technology provides Web developers with a simple, consistent mechanism for extending the functionality of a Web server and for accessing existing business systems. A servlet can almost be thought of as an applet that runs on the server side -- without a face. Java servlets have made many Web applications possible.

Servlets are the Java platform technology of choice for extending and enhancing Web servers. Servlets provide a component-based, platform-independent method for building Web-based applications, without the performance limitations of CGI programs. And unlike proprietary server extension mechanisms (such as the Netscape Server API or Apache modules), servlets are server- and platform-independent. This leaves you free to select a "best of breed" strategy for your servers, platforms, and tools.

Servlets have access to the entire family of Java APIs, including the JDBC API to access enterprise databases. Servlets can also access a library of HTTP-specific calls and receive all the benefits of the mature Java language, including portability, performance, reusability, and crash protection.