code: public void initializeConnection() throws SQLException {
      long connectionTimeoutMillis = TimeUnit.SECONDS
          .toMillis(urlParser.getOptions().validConnectionTimeout);
      lastQueryNanos = System.nanoTime();
      if (connectionTimeoutMillis > 0) {
        connectionValidationLoop.addListener(this, connectionTimeoutMillis);
      }
    }
docs: Initialize Listener. This listener will be added to the connection validation loop according to
  option value so the connection will be verified periodically. (Important for aurora, for other,
  connection pool often have this functionality)
  
  @throws SQLException if any exception occur.