You can probably get up to speed faster in storage administration faster than you can in programming, if you're more interested in the operations side of things. Just because people use fewer mainframes doesn't mean that the same old problems don't exist as far as tying up expensive online storage with data that doesn't need to be online - if it should even continue to exist as all. The main difference is that in our new, more "efficient" world, you probably wouldn't get a position solely as a storage administrator, you'd probably have a dozen other duties as well. Welcome to the 21st Century.
If you had to narrow your focus, I'd recommend bypassing EJB, although learn JPA, since it's the way to go for both EJB and Hibernate now. Struts has plenty of current openings, but a lot of them are in maintenance positions. I personally dropped Struts several years back because
JSF made me more productive. Plus it's an integral part of JEE 5 and up.
Incidentally, I come from a mainframe background myself, and I spent a few years doing storage administration as well as other things like maintaining the source code management system, administering ROSCOE, and various odds and ends. The only real downside is that I developed the habit of striving for reliability instead of hack-em-out solutions a la PCs, where if a program goes awry people just reboot. Mainframes don't re-IPL just because of a wayward app. At least we'll hope not. Unfortunately, the demand these days is mostly to "Git-R-Dun", not get it right. Gotta turn 'em out fast. And cheap. Lower Prices, Always.
