This week's book giveaways are in the iOS and Features new in Java 8 forums. We're giving away four copies each of Barcodes with iOS: Bringing together the digital and physical worlds and Core Java for the Impatient and have the authors on-line! See this thread and this one for details.
I assume you are talking about distributed apps since you mention different JVMs. Static variables are local to each JVM. So you cant share data between servlets on different JVMs. If you want to share data, you might consider using sessions or other mechanisms like a DB. For the same reason, you cannot even depend on static variables for storing any data. The container might decide to migrate your session to a new jvm where you will lose all you static vars values unless you take explicit steps with the HttpSessionActivationListener interface.