You don’t have a Date, you have a String representation of a date. You should convert the String into a Date and then obtain the milliseconds. To convert a String into a Date and vice versa you should use SimpleDateFormat class.
Here’s an example of what you want/need to do (assuming time zone is not involved here):
String myDate = "2014/10/29 18:10:45";
SimpleDateFormat sdf = new SimpleDateFormat("yyyy/MM/dd HH:mm:ss");
Date date = sdf.parse(myDate);
long millis = date.getTime();
Still, be careful because in Java the milliseconds obtained are the milliseconds between the desired epoch and 1970-01-01 00:00:00.
Using the new Date/Time API available since Java 8:
String myDate = "2014/10/29 18:10:45";
LocalDateTime localDateTime = LocalDateTime.parse(myDate,
DateTimeFormatter.ofPattern("yyyy/MM/dd HH:mm:ss") );
/*
With this new Date/Time API, when using a date, you need to
specify the Zone where the date/time will be used. For your case,
seems that you want/need to use the default zone of your system.
Check which zone you need to use for specific behaviour e.g.
CET or America/Lima
*/
long millis = localDateTime
.atZone(ZoneId.systemDefault())
.toInstant().toEpochMilli();
