public Connection getConnectionInternal() {
    try {
      if (conn == null) {
        Class.forName(driverClass);
        conn = DriverManager.getConnection(connectionString, username.orNull(), password.orNull());
      } else if (isExpired() || conn.isClosed()) {
        resetConnection();
      }
      updateExpiration();
      return conn;
    } catch (Exception e) { //IOEx., SQLEx.
      throw new RuntimeException(e);
    }
  }