public static String format(Date date) {
        return FAST_FORMAT.format(date.toInstant());
    }
Formats a Date object to String as defined in XEP-0082.

The resulting String will have the timezone set to UTC ('Z') and includes milliseconds: 
CCYY-MM-DDThh:mm:ss.sssZ

@param date the date to format
@return the formatted date
xmppserver/src/main/java/org/jivesoftware/util/XMPPDateTimeFormat.java