This week's book giveaway is in the Mac OS forum. We're giving away four copies of a choice of "Take Control of Upgrading to Yosemite" or "Take Control of Automating Your Mac" and have Joe Kissell on-line! See this thread for details.
That's your call, but typically when you need services provided by the container. This is an over simplistic answer; because the are alternatives to EJBs that provide the same or similar services, and often you can use container services without needing EJBs, but hopefully you can do a bit of exploring on the back of this and find out more for yourself.