Now I know the answer. Even though you can run wlserver6.1 with J2EE1.3 features, the Filter object expected by interal wlserver6.1 classes is according to non final
servlet 2.3 spec.
All you have to do is, add couple of methods in the custom Filter class:
setFilterConfig(FilterConfig config);
getFilterConfig();
init() method is never called.
Also you can't substitute an instance of HttpServletRequestWrapper when calling doFilter() on the FilterChain object if you run wlportal4.0 applications.
ApplicationHelper class in com.bea.p13n.management package expects an instance of weblogic.servlet.internal.ServletRequestImpl which is a final class.
Having said that, can anyone tell me if custom Filters can be implemented using HttpRequestWrapper in wl7.0?
Thanks.