The book is written as an introduction to java and OOP. I then cover the WebSphere (and non-WebSphere - like basic Windows concepts) technologies needed to create and implement client and server based apps. No real coverage of performance (Well, I discuss the adv/disadv to precompiling JSPs and why nested if are more efficient - basics). It more like learning how to drive a car not tune it. I show how to install to WAS not how WAS works internally. Re: the JDKs. I develop against the RAD JDK but install client based apps to the Oracle JDK. I've never had a problem but I'm not using any real advanced java features. If I was going to install to WAS I would develop using the RAD/IBM JDK in case there were some differences. Hope that helps.
subject: Question to Bob Janson -- Which Java to use with Websphere?