Re: help with preparedStatement.setTimestamp with Calendar

Dan Jatnieks wrote:

> 	Calendar cal = Calendar.getInstance(TimeZone.getTimeZone("EST"));
> 	Calendar utc = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
> 
> 	Date startdate = Date.valueOf("2006-01-01");
> 	cal.setTime(startdate);
> 	utc.setTime(cal.getTime());
> 
> 	String ins = "INSERT INTO t (datestamp) VALUES ( ?)";

> 		// Use the UTC Calendar to create a new timestamp and the target
> 		// Calendar to adjust it to the correct timezone and set the
> 		// timestamp value.
> 		Timestamp tstamp = new Timestamp(utc.getTimeInMillis());
> 		stmt.setTimestamp(2, tstamp, cal);


I'm pretty sure this is wrong - it will reconvert the date back to your 
timezone.  You need to specify "utc" as the last argument above, and you 
don't need to do "utc.setTime()" either:

This is also dangerous:
   Date startdate = Date.valueOf("..."); // Notice that this will also

This will parse the date in the current system timezone. Be sure to 
parse the date in the appropriate timezone first. If you meant EST, you 
need to do:

   Calendar utcCal = Calendar.getInstance(TimeZone.getTimeZone("GMT"));
   TimeZone localtz = TimeZone.getTimeZone("EST"); // or whatever

   // This is how you parse a date in a known timezone:
   SimpleDateFormat fmt = new SimpleDateFormat("yyyy-MM-dd");
   fmt.setTimeZone(localtz);
   Date startdate = fmt.parse("2006-02-01");

   // Now you need to pass that to the DB:

   PreparedStatement ps = ....;

   ps.setTimestamp(1, new Timestamp(startdate.getTime()), utcCal);

Some of this stuff can be done in advance (like setting up the 
SimpleDateFormat, though beware of sharing such a SimpleDateFormat 
between threads - either synchronize it, or make it local or thread-local).

Ditto for the utcCal object - you need to make it thread-safe yourself 
in the same way.


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