code: @Override
      public void appendTimestamp(StringBuffer buffer, Date datetime) {
          SimpleDateFormat formatter = new SimpleDateFormat(SyslogConstants.SYSLOG_DATEFORMAT_RFC5424);
          Calendar calendar = Calendar.getInstance();
          calendar.setTimeInMillis(datetime.getTime());
          String formatedTimestamp = formatter.format(calendar.getTime());
          buffer.append(formatedTimestamp);	
          buffer.append(' ');
      }
docs: /* (non-Javadoc)
  @see org.graylog2.syslog4j.impl.message.processor.AbstractSyslogMessageProcessor#appendTimestamp(java.lang.StringBuffer, java.util.Date)
  
  This is compatible with RFC5424 protocol.