public StringBuffer format(Calendar calendar, StringBuffer buf) {
        if (mTimeZone != null) {
            calendar = (Calendar)calendar.clone();
            calendar.setTimeZone(mTimeZone);
        }
        return applyRules(calendar, buf);
    }
@param pattern {@link java.text.SimpleDateFormat} compatible pattern
@param timeZone optional time zone, overrides time zone of formatted
date
@param locale optional locale, overrides system locale
@param symbols optional date format symbols, overrides symbols for
provided locale
xmppserver/src/main/java/org/jivesoftware/util/FastDateFormat.java