Java – generic Dao and service layer

I will design a Dao layer for my application My focus is that services only call Dao, which is independent of the underlying implementation

public interface GenericSearchDao{
        List getAll();
        List getByQuery(String query);
}

public class UserJdbcSearch implements GenericSearchDao{

        public List getAll(){
                // Get all users;
        }

        List getByQuery(String query){
                // Get users by query;
        }

}

public class UserFileSystemSearch implements GenericSearchDao{

        public List getAll(){
                // Get all users from file system;
        }


        List getByQuery(String query){
                // Get users by query[this leads to invalid operation];
        }
}

public userService {

        private GenericSearchDao dao = new UserFileSystemSearch();

        public List getUsers(){
                rturn dao.getAll();
        }

         public List getByQuery(String query){
               return  dao.getByQuery(query);
        }
}

Need help:

What should I do to get rid of the specific implementation of 'getbyquery', because the data storage can be RDBMS, file system, FTP, etc

How should I design my Dao layer?

If anyone says "delete getbyquery () from genericsearchdao", what should I do when I need data specific to business operations: for example, users with roles, users with products, etc

Solution

You may find this method very useful http://www.bejug.org/confluenceBeJUG/display/BeJUG/Generic +DAO+example