Does GlassFish servlet container use that catalina?

I am running the same servlet application in both Apache Tomcat and GlassFish servers.
I wanted to see the ServletConfig and ServletContext implementation class names.
Surprisingly, I found that GlassFish is also using from Apache Tomcat’s catalina classes. Is my observation correct? If yes, why isn’t GlassFish using its own servlet implementation classes?

Running a Servlet in Apache Tomcat server

[Running a Servlet in GlassFish Server2

Answer

According to this FAQ entry the Glassfish web container is a fork of Tomcat 5.5. Therefore it uses the same package names, although Tomcat’s code has evolved a lot since the fork.