Since you have been using declarative security already, you are familiar with both the advantages and disadvantrages of it. JAAS is a nice alternative, although there are other, just as good ways to implement security.
JAAS is not terribly difficult to learn, but you need to start with understanding the underlying functionality of it. Here is a
very good introduction to JAAS. It is a couple years old, but is still extremely informative. Give it a read, and then let me know what questions you can have and I can try and help out.
“Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning.” - Rich Cook