What is it?
Apache JSSI is Java servlet that provides support for including dynamic servlet output from within HTML documents via the <SERVLET> tag as specified by the JavaSoft Java Web Server.

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.

What does it do?
Apache JSSI parses JHTML files, executes the servlets (instructions) as specified by the <SERVLET> tag and replaces those tags with the output of the executed servlet. The <SERVLET> tag can be seen as the server side equivalent of the <APPLET> tag.

Note that SSI (Server Side Include) files for java servlets are called JHTML files in the apache context while SHTML files are usually for traditional SSI (like <!--#ECHO -->). This is a bit confusing since in the Java Web Server (SUN) context SHTML files are used for java servlet SSI files and JHTML is used for page compiled pages. Java Apache SSI does not support page compiling.

Servlets have access to the entire family of Java APIs, including the JDBC^TMAPI 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.

Apache JSSI is a servlet based on the JavaSoft Servlet API 2.0 and can be executed by any web server that can execute such servlets.

Today, servlets are a popular choice for building interactive web applications. Third-party servlet containers are available for Apache Web Server, iPlanet Web Server, Microsoft IIS, and others. Servlet containers can also be integrated with web-enabled application servers, such as BEA WebLogic Application Server, IBM WebSphere, iPlanet Application Server, and others.

Tomcat is the servlet container that is used in the official Reference Implementation for the Java Servlet and JavaServer Pages technologies. The Java Servlet and JavaServer Pages specifications are developed by Sun under the Java Community Process.

Tomcat is developed in an open and participatory environment and released under the Apache Software License. Tomcat is intended to be a collaboration of the best-of-breed developers from around the world. .

Tomcat is a free, open-source implementation of Java Servlet and JavaServer Pages technologies developed under the Jakarta project at the Apache Software Foundation. Tomcat is available for commercial use under the ASF license from the Apache web site in both binary and source versions.