java调用oracle函数

/**
* 调用函数取得数据表的ID值
* @param tableName 表名
* @return
* @throws SQLException
*/
public String callFun(String tableName) throws SQLException {
Connection conn = ConnectionFactory.getConnection();
CallableStatement cstmt = null;
cstmt = conn.prepareCall("{?=call getIdBySeq(?)}");
cstmt.registerOutParameter(1, Types.VARCHAR);
cstmt.setString(2, tableName);
cstmt.execute();
return cstmt.getString(1);
}

public class ConnectionFactory {

private ConnectionFactory() {
}

private static ComboPooledDataSource ds = null;

public static synchronized Connection getConnection() {
Connection con = null;
ds = new ComboPooledDataSource();
try {
con = ds.getConnection();
} catch (SQLException e1) {
e1.printStackTrace();
}
return con;
}
}