code: public void close(String line, DispatchCallback callback) {
      // close file writer
      if (sqlLine.getRecordOutputFile() != null) {
        // instead of line could be any string
        stopRecording(line, callback);
      }
  
      DatabaseConnection databaseConnection = sqlLine.getDatabaseConnection();
      if (databaseConnection == null) {
        callback.setToFailure();
        return;
      }
  
      try {
        Connection connection = databaseConnection.getConnection();
        if (connection != null && !connection.isClosed()) {
          sqlLine.info(
              sqlLine.loc("closing", connection.getClass().getName()));
          connection.close();
        } else {
          sqlLine.info(sqlLine.loc("already-closed"));
        }
      } catch (Exception e) {
        callback.setToFailure();
        sqlLine.error(e);
        return;
      }
  
      sqlLine.getDatabaseConnections().remove();
      callback.setToSuccess();
    }
docs: Closes the current connection.
  Closes the current file writer.
  
  @param line Command line
  @param callback Callback for command status