cdm/src/main/java/ucar/nc2/units/DateFormatter.java
public String toDateTimeString( Date date) {
    if (date == null) return "Unknown";
    stdDateTimeFormat();
    return stdDateTimeFormat.format( date) +"Z";
  }
public String toDateTimeString( Date date) {
    if (date == null) return "Unknown";
    stdDateTimeFormat();
    return stdDateTimeFormat.format( date) +"Z";
  }
"standard date format" = yyyy-MM-dd HH:mm:ssZ
@param date format this date
@return date formatted as date/time