Question

I have a date stored as a java.sql.Timestamp in a database. The date is “2010-01-20T19:10:35.000Z” and is equivalent to 1264014635743 ms.

Somehow, the date is formatted differently on the prod machine compared to the dev machine.

The code to format the date is:

private final static String DATE_FORMAT = "yyyy-MM-dd";
public final static SimpleDateFormat APP_DATE_FORMATER = new SimpleDateFormat(DATE_FORMAT);
private static final TimeZone UTC_TIMEZONE = TimeZone.getTimeZone("Etc/UTC");
APP_DATE_FORMATER.setTimeZone(UTC_TIMEZONE);
DateTimeZone.setDefault(DateTimeZone.UTC);

String output = APP_DATE_FORMATER.format(date)

The generated output in dev is the correct “2010-01-20”. But in prod I have “2010-01-21”, one day later!

Of course, since the error occurs on the prod server, I’m limited in my debugging options…

I have double checked, and both server have the same time and timezone. Both clock are synchronized with an ntp server.

---

[UPDATE] The database in prod has the value: “10-01-20 19:10:35,743000000” for the date field

Answer 1

My first thought is that this is a concurrency issue. SimpleDateFormat is not thread-safe, yet you’re sharing a static instance. If you need to use java.text formatters in a multi-threaded environment, you should use a ThreadLocal to hold them:

private static ThreadLocal<DateFormat> _datetimeFormatter = new ThreadLocal<DateFormat>();

private static DateFormat getDatetimeFormatter()
{
    DateFormat format = _datetimeFormatter.get();
    if (format == null)
    {
        format = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss");
        format.setTimeZone(TimeZone.getTimeZone("GMT"));
        _datetimeFormatter.set(format);
    }
    return format;
}

public static String formatDatetime(Date date)
{
    return getDatetimeFormatter().format(date);
}

It’s also possible (but unlikely) that “Etc/UTC” is not found on the server. Do you log the value from getTimeZone()?

And the third option is, to paraphrase Inigo Montoya, “you are not running the code that you think that you are running.” It could be because your presentation code didn’t properly unload on the server, or there’s another date formatter floating around.