Java Date to UTC using gson

Question

I can't seem to get gson to convert a Date to UTC time in java.... Here is my code...

Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'").create(); //This is the format I want, which according to the ISO8601 standard - Z specifies UTC - 'Zulu' time  Date now=new Date();           System.out.println(now);        System.out.println(now.getTimezoneOffset()); System.out.println(gson.toJson(now)); 

Here is my Output

Thu Sep 25 18:21:42 BST 2014           // Time now - in British Summer Time  -60                                    // As expected : offset is 1hour from UTC     "2014-09-25T18:21:42.026Z"             // Uhhhh this is not UTC ??? Its still BST !! 

The gson result I want and what I was expecting

"2014-09-25T17:21:42.026Z" 

I can clearly just subtract 1hr before the call toJson but this seems to be a hack. How can I configure gson to always convert to UTC ?

Answer 1

After some further research, it appears this is a known issue. The gson default serializer always defaults to your local timezone, and doesn't allow you to specify the timezone. See the following link.....

https://code.google.com/p/google-gson/issues/detail?id=281

The solution is to create a custom gson type adaptor as demonstrated in the link:

// this class can't be static public class GsonUTCDateAdapter implements JsonSerializer<Date>,JsonDeserializer<Date> {      private final DateFormat dateFormat;      public GsonUTCDateAdapter() {       dateFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SSS'Z'", Locale.US);      //This is the format I need       dateFormat.setTimeZone(TimeZone.getTimeZone("UTC"));                               //This is the key line which converts the date to UTC which cannot be accessed with the default serializer     }      @Override public synchronized JsonElement serialize(Date date,Type type,JsonSerializationContext jsonSerializationContext) {         return new JsonPrimitive(dateFormat.format(date));     }      @Override public synchronized Date deserialize(JsonElement jsonElement,Type type,JsonDeserializationContext jsonDeserializationContext) {       try {         return dateFormat.parse(jsonElement.getAsString());       } catch (ParseException e) {         throw new JsonParseException(e);       }     } } 

Then register it as follows :

  Gson gson = new GsonBuilder().registerTypeAdapter(Date.class, new GsonUTCDateAdapter()).create();   Date now=new Date();   System.out.println(gson.toJson(now)); 

This now correctly outputs the Date in UTC

"2014-09-25T17:21:42.026Z" 

Thanks go to the link author.