Is tomcat not an official part of Java EE?

[Varuna Seneviratna]

The Web Application part of Java EE Tutorial(https://docs.oracle.com/javaee/7/tutorial/webapp.htm#BNADR) does not list Tomcat as part of Java EE. Why is it so?

[K. Tsang]

Tomcat is not part of Java EE platform. It is a web container that implements Java EE stack (servlet & JSP, no EJB)

The Java EE tutorial use Glassfish which is a reference implementation of the full Java EE stack.

[Jeanne Boyarsky]

Also, there are other servers such as WebSphere and JBoss that implement Java EE. They aren't part of the Java EE either.

[Tim Holloway]

Java EE is the specification. Tomcat is simply one (partial) implementation of that specification. But then again, so is jetty. Glassfish, JBoss/Wildfly, WebLogic Server, IBM's WebSphere, the JoNaS server, all implementations. The spec is strictly documentation, not products. Unlike Microsoft's Office suite, where the specification is ultimately dependent on an implementation (Microsoft's own products).

Sun/Oracles does provide what's known as reference implementations of their specs. For example, Mojarra for JavaServer Faces. I understand that Tomcat served as the reference implementation for the servlet/JSP spart of the J2EE spec, but was supposedly abandoned in favor of Glassfish.

A reference implementation isn't all that special. What it means is basically that that is the platform that Sun/Oracle uses to proof/demonstrate the specification implementation. the Java specs are the final definition, even about the reference implementation. Oracle will quite cheerfully apply a battery of validation tests to any implementation of that spec - for a fee, of course - and if the product in question passes, will certify it.