Although I can just about imagine an application with a Swing UI that also serves HTTP requests, it does not really make sense to do both these functions in a single class.
Apart from anything else, the great majority of
Servlets extend from GenericServlet or HttpServlet, and thus cannot also extend from JPanel. While you could get round this by implementing the basic javax.servlet.Servlet interface in your JPanel class, it would be very weird indeed to have a JPanel created and managed by a web server.
Can you explain a bit more about what you are trying to achieve by doing this?