Hi Lakshmi:
Clean seperation of business rules, presentation and data access is essential for good design of a web app (n-tier design).
You can use MVC based frameworks like
Struts for this. You can use the DAO
pattern to implement data access for your application.
Depending on how you are implementing your business rules (
EJB or Java Beans), you can invoke your DAO's from there.
Look for the DAO pattern on Sun's website.
Hope this helps.