Java Timestamp - How can I create a Timestamp with the date 23/09/2007?

What about this?

java.sql.Timestamp timestamp = java.sql.Timestamp.valueOf("2007-09-23 10:10:10.0");

By Timestamp, I presume you mean java.sql.Timestamp. You will notice that this class has a constructor that accepts a long argument. You can parse this using the DateFormat class:

DateFormat dateFormat = new SimpleDateFormat("dd/MM/yyyy");
Date date = dateFormat.parse("23/09/2007");
long time = date.getTime();
new Timestamp(time);

What do you mean timestamp? If you mean milliseconds since the Unix epoch:

GregorianCalendar cal = new GregorianCalendar(2007, 9 - 1, 23);
long millis = cal.getTimeInMillis();

If you want an actual java.sql.Timestamp object:

Timestamp ts = new Timestamp(millis);