I have chosen to go the JEE route for a career path but I have been having a hard time determining which core technologies that I need to be most familiar with. I'm at the point I can write web apps without a problem with JSP's and regular servlets using JDBC or some basic Hibernate stuff (I know, HTML, CSS and have used MVC extensively on a number of different platforms). What I'm trying to find out is if there is some standard as far as J2EE technologies go.

When I look at most of the Job listings, occasionally you will see someone mention Struts or Spring but rarely do I see any mention of EJB's. So my question is really, are EJB's basically required by most JEE employers? Or are most of them working with POJO's? Is it a mix?

I have a hard time figuring out if I should put the majority of my time into Struts, Spring/Hibernate, EJB's, etc. And if I do need to master EJB's what version should I learn? 2.1 or 3.0. 3.0 has some obviously better features but I figure a lot of companies probably chose to write their apps in 2.1 just because it was the standard of the time and now migrating would be a big deal.

Any advice on this is greatly appreciated.