Java's web technology has always been my fascination. This book opened up a whole new perspective on Java and JSP for me.
The book that I truly started learning JSP with is "More Servlets and Java Server Pages" by Marty Hall. That book breaks down piece by piece how it all works. It's a really great book. "Pro JSP" shows you how to exploit that knowledge to turn it into something truly useful. If you are a Java web developer you know that Java web applications can be slow and clumsy. Have you ever wondered how the sites like Amazon are written in Java and can handle millions of hits a day? Well, that book explains the technology behind those kinds of applications.
The book makes very extensive use of EL (not something I am very fond of). It shows you how far you can go with JSTL by utilizing it in creating Java Server Faces. So it doesn't just tell you how amazing JSTL is because it can connect to a MySQL db from a jsp page (I mean maybe hardcore PHP programmers would find that feature cool. I don't). As far a JSF, the book shows very clearly how to do it. And you can easily try it out on your server. Still I do not believe the book does a good job providing examples of when you would really need the JSF technology. It's pretty much up to the reader's imagination. The book does a good job breaking down the use of managed beans in the context of JSF.
I think the coolest chapter of the book is the chapter on filters. Let me tell you I still have hard time comprehending the entire filtering technology in JSP. It's a really advanced topic. I had no idea you could control users' requests to that extent. The book shows graphs on how requests to your web application travel through layers of filters. So it's really clear as to when you need a filter in your applications. And it's not hard to figure out how to optimize your application's performance using filters.
I can really go forever, so I will stop here and let you see the rest for yourself.