public static DatabaseSourceDriver getDatabaseSourceDriver(String userName, String passWd){
		try{
			 Class.forName(prefetchDriverClassName);
			 Class.forName(writeDriverClassName);
			 //System.out.print("get mysql source Driver~");
			 return new MysqlDatabaseSourceDriver(prefetchConnectionString, writeConnectionString, userName, passWd);
		 } catch(Exception ex){
			 logger.log(Level.SEVERE, "get database source:", ex);
		 }
		 return null;
	}