Hi Satish,
Since you are a beginner, the best option for you would be to get hold of a copy of Core Servlets by Marty Hall (or checkout
http://www.coreservlets.com for free versions), install
Tomcat as instructed and play with building simple servlets and JSP pages and get to know what the technology is about.
An advanced book would be More Servlets and JSPs by the same author (
http://www.moreservlets.com).
For certification purposes so far the best book has been the Manning publications book (by Desmukh & Malaviya)for JSP 1.2 & Servlets 2.3 specs - a more recent and most welcome addition is "Head First Servlets and JSP" by Sierra & Bates for the latest specs and latest certification exam. Note, this isn't just a certification book but a good text book too - so if you want to buy just one book - this might be the right one for you.
I personally like Marty Hall's style too and at the same time am a fan of any book by Sierra & Bates.
But, again, since you are a beginner, there is no substitute for a hands on text/tutorial book like coreservlets to give you an introduction to the subject.
Hope this helps and good luck!
- ortimuS