code: @Override
      public ListServersResult listServers(ListServersRequest request) {
          request = beforeClientExecution(request);
          return executeListServers(request);
      }
docs: <p>
  Lists the Secure File Transfer Protocol (SFTP) servers that are associated with your AWS account.
  </p>
  
  @param listServersRequest
  @return Result of the ListServers operation returned by the service.
  @throws ServiceUnavailableException
  The request has failed because the AWS Transfer for SFTP service is not available.
  @throws InternalServiceErrorException
  This exception is thrown when an error occurs in the AWS Transfer for SFTP service.
  @throws InvalidNextTokenException
  The <code>NextToken</code> parameter that was passed is invalid.
  @throws InvalidRequestException
  This exception is thrown when the client submits a malformed request.
  @sample AWSTransfer.ListServers
  @see <a href="http://docs.aws.amazon.com/goto/WebAPI/transfer-2018-11-05/ListServers" target="_top">AWS API
  Documentation</a>