CODEWITHSUNDEEP
javagwt
quarks
quarks

Reputation: 35276

Create ISO 8601 date String with GWT

Here's my code:

public static String getStringFormat(Date inputDate, String timeZone){
        String strFormat = null;
        try{
            final TimeZone computedTimeZone = TimeZone.createTimeZone(TimeZoneInfo.buildTimeZoneData(timeZone));
            DateTimeFormat dateTimeFormat = DateTimeFormat.getFormat(DateTimeFormat.PredefinedFormat.ISO_8601);
            strFormat = dateTimeFormat.format(inputDate, computedTimeZone);
            Date d = new Date(strFormat);
            strFormat = dateTimeFormat.format(d, TimeZone.createTimeZone(0));
            String[] s = strFormat.split("\\+");
            strFormat = s[0];
        }catch(Exception e){
            Console.log(e.getMessage());
        }
        return strFormat;
    }

For input, new Date() and Etc/GMT+3 this function returns null. What could be wrong?

Error

Error: NullPointerException: undefined
    at NBF_g$.QBF_g$ [as createError_0_g$] (NullPointerException.java:40)
    at NBF_g$.ub_g$ [as initializeBackingError_0_g$] (Throwable.java:113)
    at NBF_g$.bb_g$ (Throwable.java:61)
    at NBF_g$.Ib_g$ (Exception.java:25)
    at NBF_g$.avq_g$ (RuntimeException.java:25)
    at NBF_g$.gfs_g$ (JsException.java:34)
    at new NBF_g$ (NullPointerException.java:27)
    at new wou_g$ (JSONString.java:43)

Upvotes: 0

Views: 311

Answers (1)

Colin Alworth
Colin Alworth

Reputation: 18331

The method TimeZoneInfo.buildTimeZoneData(String tzJSON) doesn't accept the name of the zone, but needs a JSON string full of the details of how that zone works. It turns out that the browser doesn't come to you with all of the details of how all time zones work, so your app has to already be prepared to handle them.

GWT ships with all of the timezones (though they are currently a little out of date, and should be updated in this next release), but you have to tell the compiler which ones you want, or it will compile them out. The full list of all possible timezones and their offsets, etc is not small, so I would encourage you to limit the list.

These are stored in the constants interface TimeZoneConstants. Here is how you might use it: 

TimeZoneConstants constants = GWT.create(TimeZoneConstants.class);

// This is the shorthand for TimeZone.createTimeZone(TimeZoneInfo.buildTimeZoneData(...))
TimeZone computedTimeZone = TimeZone.createTimeZone(constants.americaAdak());
//...

If you want to use the timezone string instead, say, passed from the server, you could build a map of the possible timezones that are supported. Be aware though that the full map is very large (200KB just for the timezones in the "America/..." group).

computedTimeZone = TimeZone.createTimeZone(constants.americaAdak());
zones.put(computedTimeZone.getID(), computedTimeZone);
computedTimeZone = TimeZone.createTimeZone(constants.americaAnchorage());
zones.put(computedTimeZone.getID(), computedTimeZone);
computedTimeZone = TimeZone.createTimeZone(constants.americaAnguilla());
zones.put(computedTimeZone.getID(), computedTimeZone);
//...

Then you can read out a specific item from the map as needed:

String tzName = Window.prompt("Enter a timezone name", "America/Chicago");

DateTimeFormat dateTimeFormat = DateTimeFormat.getFormat(DateTimeFormat.PredefinedFormat.ISO_8601);
String strFormat = dateTimeFormat.format(inputDate, zones.get(tzName));
//...

In your comment, you clarified the question, that you only need to deal with offsets, not the full TimeZone string format, i.e. Etc/GMT+3, meaning "Offset of +3 hours from GMT". This is easier to handle - simply parse out the +3 into a number, and use the TimeZone.createTimeZone(int timeZoneOffsetInMinutes) method. This will not understand daylight savings time, but that wouldn't be possible without the full name of the timezone or list of offsets, etc (which gets to why that JSON is so large).

//TODO, implement parse(), don't forget about negative numbers
int offsetInHours = parse(timeZone);
TimeZone computedTimeZone = TimeZone.createTimeZone(60 * offsetInHours);
//...

Upvotes: 1

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