Java can build XML documents(building) or can extract data form XML
documents(This is called parsing). The bottom line is that Java manipulates the
data in the XML documents.

Actually where is XML used and how is it used from a java  programmer point of
view in JSP, Servlets and struts.

Can u tell me any good site, also from interview point of view.Generally what
are the questions that are asked in an interview for an experienced person about
XML.

the main purpose of XML is to act as a deployment descriptor for web
applications which is comprised of JSP and servlet so that you need not to
hardcode the values is the code.

one good site is www.w3schools.com

See chapter 2 at: http://java.sun.com/j2ee/1.4/docs/tutorial/doc/