There's a whole bunch of web servers out there. Tomcat, Resin, Orion, JRun... then you have application servers that also serve up
JSP's and servlets, like BEA Weblogic, Oracle 9i, Websphere,
JBoss. Some of those actually use Tomcat or some other web server within the application server, some have their own. All sorts of servers out there. That's why it is REALLY important to make your web applications portable, and not dependent on one specific implementation. Luckily,
Java makes it easy for you to do this