private void initColumnName(ResultSet rs) throws SQLException {
		if (columnNameSet.isEmpty()) {
			synchronized (columnNameSet) {
				if (columnNameSet.isEmpty()) {
					ResultSetMetaData metaData = rs.getMetaData();
					int columnCount = metaData.getColumnCount();
					for (int i = 1; i <= columnCount; i++) {
						columnNameSet.add(metaData.getColumnName(i));
						columnClassName.put(metaData.getColumnName(i), metaData.getColumnClassName(i));
					}
				}
			}
		}

	}