GSON - Date format

Question

I m trying to have a custom date format in Gson output  but  setDateFormat DateFormat FULL  doesn t seem to work and it the same with  registerTypeAdapter Date class  new DateSerializer      It s like Gson doesn t care about the object  Date  and print it in its way   How can I change that   Thanks  EDIT     Entity public class AdviceSheet     public Date lastModif           public void method      Gson gson   new GsonBuilder   setDateFormat DateFormat LONG  create       System out println gson toJson adviceSheet       I always use java util Date  setDateFormat   doesn t work

User · Answer

As M L  pointed out  JsonSerializer works here  However  if you are formatting database entities  use java sql Date to register you serializer  Deserializer is not needed   Gson gson   new GsonBuilder       registerTypeAdapter java sql Date class  ser  create      This bug report might be related  http   code google com p google-gson issues detail id 230  I use version 1 7 2 though

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I m on Gson 2 8 6 and discovered this bug today   My approach allows all our existing clients  mobile web etc  to continue functioning as they were  but adds some handling for those using 24h formats and allows millis too  for good measure   Gson rawGson   new Gson    SimpleDateFormat fmt   new SimpleDateFormat  MMM d  yyyy HH mm ss   private class DateDeserializer implements JsonDeserializer lt Date gt         Override     public Date deserialize JsonElement json  Type typeOfT  JsonDeserializationContext context              throws JsonParseException           try               return new rawGson fromJson json  Date class             catch  JsonSyntaxException e             String timeString   json getAsString            log warning  Standard date deserialization didn t work     timeString           try               return fmt parse timeString             catch  ParseException e             log warning  Parsing as json 24 didn t work     timeString           return new Date json getAsLong              Gson gson   new GsonBuilder        registerTypeAdapter Date class  new DateDeserializer         create      I kept serialization the same as all clients understand the standard json date format   Ordinarily  I don t think it s good practice to use try catch blocks  but this should be a fairly rare case

User · Answer

This won t really work at all  There is no date type in JSON  I would recommend to serialize to ISO8601 back and forth  for format agnostics and JS compat   Consider that you have to know which fields contain dates

User · Answer

In case if you hate Inner classes  by taking the advantage of functional interface you can write less code in Java 8 with a lambda expression   JsonDeserializer lt Date gt  dateJsonDeserializer          json  typeOfT  context  - gt  json    null   null   new Date json getAsLong     Gson gson   new GsonBuilder   registerTypeAdapter Date class dateJsonDeserializer  create

User · Answer

You can specify you format Gson gson   builder setDateFormat  yyyy-MM-dd   create       in this method instead of yyyy-MM-dd you can use anyother formats    GsonBuilder builder   new GsonBuilder                            builder registerTypeAdapter Date class  new JsonDeserializer lt Date gt                                  public Date deserialize JsonElement json  Type typeOfT  JsonDeserializationContext context  throws JsonParseException                                   return new Date json getAsJsonPrimitive   getAsLong                                                                                        Gson gson   builder setDateFormat  yyyy-MM-dd   create

User · Answer

This is a bug  Currently you either have to set a timeStyle as well or use one of the alternatives described in the other answers

User · Answer

It seems that you need to define formats for both date and time part or use String-based formatting  For example   Gson gson   new GsonBuilder       setDateFormat  EEE  dd MMM yyyy HH mm ss zzz   create      or using java text DateFormat  Gson gson   new GsonBuilder       setDateFormat DateFormat FULL  DateFormat FULL  create      or do it with serializers   I believe that formatters cannot produce timestamps  but this serializer deserializer-pair seems to work  JsonSerializer lt Date gt  ser   new JsonSerializer lt Date gt         Override   public JsonElement serialize Date src  Type typeOfSrc  JsonSerializationContext               context        return src    null   null   new JsonPrimitive src getTime             JsonDeserializer lt Date gt  deser   new JsonDeserializer lt Date gt         Override   public Date deserialize JsonElement json  Type typeOfT         JsonDeserializationContext context  throws JsonParseException       return json    null   null   new Date json getAsLong             Gson gson   new GsonBuilder       registerTypeAdapter Date class  ser      registerTypeAdapter Date class  deser  create      If using Java 8 or above you should use the above serializers deserializers like so   JsonSerializer lt Date gt  ser    src  typeOfSrc  context  - gt  src    null   null               new JsonPrimitive src getTime      JsonDeserializer lt Date gt  deser    jSon  typeOfT  context  - gt  jSon    null   null   new Date jSon getAsLong

User · Answer

Gson gson   new GsonBuilder   setDateFormat  yyyy-MM-dd T HH mm ss SSSZ   create      Above format seems better to me as it has precision up to millis

[java] GSON - Date format

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