I have a portlet with JSR 168 specification which used to run inside UPortal (some old portal based framework for java). However, I need to take this portlet off the portal and make it as an standalone app. Now my question is if there is any way to that with existing code or do it need to create a new webapp? (obv I am sure I could reuse some of the old code but only some)
Portlets are managed to live inside a Portlet Container and cannot be deplyed on a straightforward Servlet Container, whereas a webapp which is a set of routed Servlets thus only needs a Servlet Container (Except if you will be shipped Entreprise Beans)
So you guessed right, there will parts to rewrite such as web application deployment descriptor (web.xml), pages handling, styles... But if you have managed to have a solid base design for your portlet application, I guess you will be able to keep almost the major part of your sources since they will be in separate layers.