My application is loading a custom handler class which is outside my applications WEB-INF directory. Now this class which i am trying to load is implenting a public interface(<myinterface>

present in a jar file in WEB-INF/lib directory of my application.Am getting this NoClassDefFoundError:<pkg_structure>.<myinterface> while trying to load my custom handler class.
But if i put this custom handler class which i am trying to load inside my WEB-INF its working fine.
Now what could be the problem? Somebody please help me out.This is urgent.TIA.