GSON - Date format

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.


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<Date> ser = new JsonSerializer<Date>() {
  @Override
  public JsonElement serialize(Date src, Type typeOfSrc, JsonSerializationContext 
             context) {
    return src == null ? null : new JsonPrimitive(src.getTime());
  }
};

JsonDeserializer<Date> deser = new JsonDeserializer<Date>() {
  @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<Date> ser = (src, typeOfSrc, context) -> src == null ? null
            : new JsonPrimitive(src.getTime());

JsonDeserializer<Date> deser = (jSon, typeOfT, context) -> jSon == null ? null : new Date(jSon.getAsLong());

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<Date> dateJsonDeserializer = 
     (json, typeOfT, context) -> json == null ? null : new Date(json.getAsLong());
Gson gson = new GsonBuilder().registerTypeAdapter(Date.class,dateJsonDeserializer).create();

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.

Tags:

Java

Gson