public List<Person> getMemberList( int group_id ){
		if( !handler_group.initialize() || !handler_person.initialize() ){
			System.out.println( "GroupServer : failed to initialize group and person hander!" );
			return null;
		}
		List<Person> list = handler_group.getMemberList( group_id );
		if( list == null ){
			handler_group.close();
			handler_person.close();
			return null;
		}
		for( Person person : list ){
			person.name = handler_person.getNameById( person.id );
		}
		handler_group.close();
		handler_person.close();
		return list;
	}