public static String formatPeriod(final long startMillis,final long endMillis,final String format){
  return formatPeriod(startMillis,endMillis,format,true,TimeZone.getDefault());
}

public static String formatPeriod ( final long startMillis , final long endMillis , final String format ) { return formatPeriod ( startMillis , endMillis , format , true , TimeZone . getDefault ( ) ) ; }
< p > formats the time gap as a string , using the specified format . padding the left hand side of numbers with zeroes is optional .
