Although JSP has a tiny fraction of the installed base of PHP and ASP, and numbers of specialist servlet web servers are completely dwarfed by Apache and Microsoft-IIS, Java related technology has a much bigger impact on the Web than the raw site numbers suggest. Over the last year JSP has been the fastest growing scripting technology after ASP.NET. JSP sites are often bigger, more complex, and better funded and run by larger organisations than sites using the more common scripting technologies.
The higher investment on these sites makes them attractive targets for hosting and site development companies, while the relatively large number of players in the application server market means that they are likely recipients of competitive upgrade offers. With Windows 2003 launching later on this month and providing some application server functionality out of the box, it is also likely that Java based sites will be strenuously encouraged to evaluate the .Net Framework.
Tracking sites using Java based application servers is not straightforward, and often requires inspection of the site content. In particular, sites using Microsoft-IIS or Netscape-Enterprise as a web server may be running servlet engines that do not provide a signature in the HTTP server header and tracking these servers has to be done through analysis of the site content.
With the proviso that a better and more accurate view can be had by taking more content from the site, and that sites using Servlet Engines with Apache, Microsoft and SunONE web servers would be not be included by this view, it is still possible to take a quick and simple view of what is going on from the HTTP server headers.
From the table, Resin, Tomcat, IBM and Oracle are popular choices for those websites that support Java-based web applications.
This is not an exhaustive list of servlet engines - for example some older engines, such as Apache JServ, still have a wide presence across the net, but are now deprecated in favour of newer implementations.
(*) The high ratio of sites per address for JRun are caused by two hosts that support many thousands of sites.