Ah, this is a very good question.
Let me say a few things to help people figure out whether this book is going to be helpful to them.
This book was written to be the best possible guide to using the
Java Persistence API (JPA) part of the spec. In order to make the book a decent size (big enough to contain in-depth information but not so big that it was onerous to carry around) we could not spend time on the component portion of the spec. We did give an overview chapter on it so that readers got an introduction to that part, but the book is really focused on JPA. We tried to keep it free from other distracting content so that it can be used as a good JPA reference. As such, we believe it is the most detailed and helpful book on JPA that is available.
The Enterprise JavaBeans 3.0 contains more general information about the spec and I believe contains EJB 2.1 content as well. If you do not know EJB 2.1 and want a reference book that includes EJB 2.1 as well then this book will likely be a better one for you. Bill Burke did most of the writing of this book, I believe, and he was also with me on the spec group (and contributed quite a lot of work on the spec, for which we are thankful!) so he knows his stuff as well. It will also contain useful info on using such component technologies as interceptors, etc, so I would recommend his book as a companion to ours.
The Mastering EJB book is frankly a book that I do not know much about. It was not written by anyone on the specification group, so I guess they must have just read the spec and written about it. As far as I am concerned if they do not have any more insight on the spec than anyone else I don't see as much value in such a book, but that may just be me. I would rather read a book written by the people that wrote the spec and know it the best. Like I say, though, I don't know the book or the authors at all, so I can't comment on its content.
Hope this helps a little, though.
-Mike
