Gson - Date Format

GSON - Date format

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());

GSON to JSON conversion - long format and simple date format yyyy-MM-dd'T'HH:mm'Z'

Please try following code:

public class Main {

    static final String DATE_FORMAT = "yyyy-MM-dd'T'HH:mm'Z'";
    static final Calendar calendar = Calendar.getInstance();

    static class LongUtil {
        static boolean isLong(String longValue) {
            try {
                Long.parseLong(longValue);
                return true;
            } catch (RuntimeException e) {
                return false;
            }

        }
    }

    static class DateDeserializer implements JsonDeserializer<Date> {

        final SimpleDateFormat simpleDateFormat = new SimpleDateFormat(DATE_FORMAT);

        @Override
        public Date deserialize(JsonElement jsonElement, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {
            System.out.println(type.getTypeName());
            System.out.println(jsonElement.getAsJsonPrimitive());
            if (jsonElement.getAsJsonPrimitive() != null) {
                final String expectedDateValue = jsonElement.getAsJsonPrimitive().getAsString();
                if (LongUtil.isLong(expectedDateValue)) {
                    System.out.println("It is long value hence parsing it to long");

                    calendar.setTimeInMillis(Long.parseLong(expectedDateValue));
                    return calendar.getTime();
                } else {
                    System.out.println("It is dateformat value hence parsing it to dateformat");
                    try {
                        return simpleDateFormat.parse(expectedDateValue);
                    } catch (ParseException e) {
                        throw new JsonParseException("Invalud dateFormat while parsing");
                    }
                }
            } else {
                throw new JsonParseException("JSOn Premitive Exception null");
            }
        }
    }

    public static void main(String[] args) throws IOException {
        GsonBuilder builder = new GsonBuilder();
        builder.registerTypeAdapter(Date.class, new DateDeserializer());
        Gson gson = builder.create();
        Type userListType = new TypeToken<ArrayList<Wrapper>>() {
        }.getType();
        File file = new File("response.json");
        System.out.println("file exists : " + file.exists());
        JsonReader jsonReader = new JsonReader(new FileReader(file));

        List<Wrapper> wrapper = gson.fromJson(jsonReader, userListType);

        System.out.println(wrapper);
    }

    class Wrapper {
        User instance;

        @Override
        public String toString() {
            return "Wrapper{" +
                    "instance=" + instance +
                    '}';
        }
    }

    class User {
        Location location;
        Date timeAtLocation;

        @Override
        public String toString() {
            return "User{" +
                    "location=" + location +
                    ", timeAtLocation='" + timeAtLocation + '\'' +
                    '}';
        }
    }

    class Location {
        String lat;
        String lon;
        Date timestamp;

        @Override
        public String toString() {
            return "Location{" +
                    "lat='" + lat + '\'' +
                    ", lon='" + lon + '\'' +
                    ", timestamp='" + timestamp + '\'' +
                    '}';
        }
    }
}

Explaination:

While deserializing i am checking if the input string is either in dateformat or in long and based on that I create the calendar instance, then i set long and finally get date object date otherwise just use the string and format it based on date formatter.

Output:

file exists : true
It is long value hence parsing it to long
It is dateformat value hence parsing it to dateformat
It is long value hence parsing it to long
It is dateformat value hence parsing it to dateformat
[Wrapper{instance=User{location=Location{lat='31.522291', lon='-96.532816', timestamp='Fri May 01 13:49:08 IST 2020'}, timeAtLocation='Thu Apr 23 04:59:00 IST 2020'}}, Wrapper{instance=User{location=Location{lat='31.522291', lon='-96.532816', timestamp='Fri Jan 24 10:12:00 IST 2025'}, timeAtLocation='Mon Dec 23 04:59:00 IST 2019'}}]

GSON: Is there any way to return 2 different date formats while marshalling

If you define a "date" a java.util.Date where hours, minutes and seconds are equal to zero, and "date with time" a Date where they are not. You coud do something like that:

    GsonBuilder builder = new GsonBuilder();
    builder.registerTypeAdapter(Date.class, new CustomDateJsonSerializer());

with CustomDateJsonSerializer define like this:

public class CustomDateJsonSerializer implements JsonSerializer<Date>, JsonDeserializer<Date> {
    private static final TimeZone UTC_TIME_ZONE = TimeZone.getTimeZone("UTC");
    private static final Pattern DATE_PATTERN = Pattern.compile("\\d{4}-\\d{2}-\\d{2}");
    private static final Pattern DATE_TIME_PATTERN = Pattern.compile("\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}:\\d{2}");

    public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        String asString = json.getAsString();
        try {
            if (DATE_PATTERN.matcher(asString).matches()) {
                return getDateFormat().parse(asString);
            } else if (DATE_TIME_PATTERN.matcher(asString).matches()) {
                return getDateTimeFormat().parse(asString);
            } else {
                throw new JsonParseException("Could not parse to date: " + json);
            }
        } catch (ParseException e) {
            throw new JsonParseException("Could not parse to date: " + json, e);
        }
    }

    private static DateFormat getDateFormat() {
        SimpleDateFormat simpleDateFormat = new SimpleDateFormat("YYYY-MM-dd");
        simpleDateFormat.setTimeZone(UTC_TIME_ZONE);
        return simpleDateFormat;
    }

    private static DateFormat getDateTimeFormat() {
        SimpleDateFormat dateFormat = new SimpleDateFormat("YYYY-MM-dd HH:mm:ss");
        dateFormat.setTimeZone(UTC_TIME_ZONE);
        return dateFormat;
    }

    public JsonElement serialize(Date date, Type typeOfSrc, JsonSerializationContext context) {
        Calendar calendar = Calendar.getInstance(UTC_TIME_ZONE);
        calendar.setTime(date);
        int hours = calendar.get(Calendar.HOUR);
        int minutes = calendar.get(Calendar.MINUTE);
        int seconds = calendar.get(Calendar.SECOND);
        String dateFormatted;
        if (hours == 0 && minutes == 0 && seconds == 0) {
            dateFormatted = getDateFormat().format(date);
        } else {
            dateFormatted = getDateTimeFormat().format(date);
        }
        return new JsonPrimitive(dateFormatted);
    }
}

Gson to json conversion with two DateFormat

I was facing the same issue. Here is my solution via custom deserialization:

new GsonBuilder().registerTypeAdapter(Date.class, new DateDeserializer());

private static final String[] DATE_FORMATS = new String[] {
        "MMM dd, yyyy HH:mm:ss",
        "MMM dd, yyyy"
};

private class DateDeserializer implements JsonDeserializer<Date> {

    @Override
    public Date deserialize(JsonElement jsonElement, Type typeOF,
            JsonDeserializationContext context) throws JsonParseException {
        for (String format : DATE_FORMATS) {
            try {
                return new SimpleDateFormat(format, Locale.US).parse(jsonElement.getAsString());
            } catch (ParseException e) {
            }
        }
        throw new JsonParseException("Unparseable date: \"" + jsonElement.getAsString()
                + "\". Supported formats: " + Arrays.toString(DATE_FORMATS));
    }
}

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