Quick answer: You don't. You can't change the interface of a core service. What you can do is to create your own service and have that delegate to UserLocalService instead.
In service.xml define your own service (or entity), e.g. "ExtendedUser", but don't give any columns - e.g. make it an empty entity.
In ExtendedUserLocalService, implement like this (pseudocode):
public class ExtendedUserLocalServiceImpl ... {
//New method
public String customMethod(long userId)
throws PortalException, SystemException {
User user = UserLocalServiceUtil.getUserById(userId);
// do something custom with user
return user.getName()
}
}
The interface UserLocalService is defined in portal-service.jar. You simply can't change it (and you wouldn't want to do it because it would introduce all kinds of compatibility and maintenance issues. Just
delegating to UserLocalService does the trick without all the negative side effects.
