Gopi,
I too am going to be taking the SCJP soon and then want to move on to the SCWCD. One the best ways to learn is to write and
test code so you will need a good servlet engine. You can do a search on this forum or the servlet forum for links. Also, you will probably want a good book and I would recommend two books by Marty Hall. His most recent which would be most relevant to the SCWCD can be found at
moreservlets.com, but his first book has a lot of good examples for learning also and is available for free in pdf format
here.