We have an application (developed before 4 years) written using JSP, Servlets and JDBC (Informix database.)

We have decided to use Hibernate to replace the old style JDBC Connection & SQL query's. We are not able to decide if we should keep the JSP/Servlets or write it again in Struts.

Here is a question I would like to ask you.

a) Are there any special advantages (in addition to the ones we have if we use Hiberante and Struts separately) of using struts and Hibernate together ?

I have a similar setup (Hibernate + Struts + other bits).

I am tempted to answer 'no' to your question. Hibernate and Struts are each pretty much totally oblivious of the other.

Each is a tremendous piece of software, and they happen to work well together. But I think if you choose to go for Struts, you'll do so on Struts's own merits, regardless of Hibernate.

(Given your pre-existing setup, I would be tempted to suggest you give a serious look at Spring, which is completely modular. You start by using Spring's ORM component along with Hibernate, and as you go, either Struts provides the MVC framework or Spring does. Only thing with Spring: steel yourself for a flourish of acronyms and lots of talk about "Aspect programming"...)

Now, I am fairly novice with all those questions: only four months of experience. So, don't rely on my comment only! Good luck!