We have an existing enterprise application which is running on JEE container.
Now to introduce OSGi on top of this for more security/robustness and other goodies from OSGi how much work is needed?
Does this book talk about any case studies? If yes, I would definitely need this book.
Yes, the book (OSGi in Depth) does talk about how to layer an OSGi framework on top of other frameworks (i.e. containers), such as JEE.
More importantly, it also shows you how to interact with JEE services, such as JNDI, data-source, HTTP request/response stack, etc, through OSGi.
In my mind, the reason for doing this (layering) is two-fold:
1) You will get a better modular application, and therefore more maintainable. For example, you could change parts of an application (i.e. interface) without impacting other pieces (i.e. business).
2) You will be able to support a more dynamic environment. For example, again being able to dynamically change the business part of an application without re-deploying the app.
The amount of work varies. If the application is already modular, than it may be trivial, and consist of writing a BundleActivator, for example. However, keep in mind, that interacting with JEE services through OSGi may need some re-factoring of code.