Hello Hdi,
The SCWCD exam depends on the
SCJP (
Java Programmer) exam. You must have passed the SCJP before attempting the SCWCD.
I can give you advice on studying for the SCWCD, but I'm a bit biased so I hope others will chime-in with their opinions. I would recommend a three-fold strategy: (a) read Head First
Servlets and JSPs and do all of the exercises and mock exams, (b) write a fairly rich webapp from scratch, and (c) read the specifications for topics that you still do not understand after doing steps (a) and (b).
Cheers,
Bryan (co-author of HFSJ ;-)