I've been using SQLJ for some time now, and there's no question SQLJ is going to be THE way to access an Oracle database using Java - SQLJ is a lot easier to use than JDBC.
This book introduces the subject of SQLJ and Oracle in a well organized manner, and also covers the advances features like including SQLJ in Enterprise JavaBeans. This book even covers the new Oracle9i features.
Up to this point, I was frustrated by the lack of decent books on SQLJ. One of the things I really liked about this book is that the programs and database scripts actually work!
If you want to learn SQLJ, this is the ONLY book worth buying.