final SimpleDateFormat ISO8601UTC = new SimpleDateFormat("yyyy-MM-dd'T'hh:mm:ss,SSS'Z'");//
24 characters
ISO8601UTC.setTimeZone(TimeZone.getTimeZone("UTC")); // UTC ==
GMT
System.out.println(ISO8601UTC.format(new Date(987654321012L)));//
2001-04-19T04:25:21,012Z
SimpleDateFormat, TimeZone, and Date are part of the standard JDK.