Is the GWT TimeZone offset backwards?

Question

I'm using com.google.gwt.i18n.client.timezone to try and display a date (as at the server), but GWT automatically adds the current timezone to the date when formatting it, meaning The wrong date is shown in different timezones.

To combat this, I'm sending the server's timezone offset to the client and using that when formatting.

I live in Australia and the current timezone is +11 GMT/UTC, but the default timezone being displayed when I format the date is -11 GMT.

The offset from the server is +11 hours (as it should be), but when I try and format the date with this offset, I get the wrong date, and so I need to use the negative offset instead.

Why is the default timezone wrong?

Answer 1

When you are getting a date (particularly if you're parsing a date) make sure you specify the timezone. GWT's DateTimeFormat.parse only supports "RFC format" timezones, something like -0800 for Pacific time. If your server is sending dates in strings to the client, make sure it includes the timezone in this format.

Then when you convert the date to a string to present it to the user, make sure you use the overload of DateTimeFormat.format that specifies a TimeZone and pass the timezone that you want the date to be presented in (the timezone of the server, in your case.)

By default dates are presented in the timezone that the user's system is set to. Setting the default timezone in GWT (so you can ignore timezones and do everything in the server's timezone) is an open issue (3489) at the time I write this.