Hi venkatesh,
Welcome to Javaranch.
What you're trying to do is very common.
Search this, our HTML/Javascript forum, and/or Google for
'cascading select lists' or dependent 'select lists' and
you should find plenty of solutions.
This is commonly done using AJAX (which is discussed in our HTML forum).
One thing to keep in mind when asking or searching about this is that HTML (and thus
JSP) does not
have a
'combo box' control.
It does have a select list which is commonly called a dropdown list.
-Ben
[ April 25, 2008: Message edited by: Ben Souther ]