"Unparseable date: 1302828677828" trying to deserialize with Gson a millisecond-format date received from server

Alfonso's comment:

Finally I got the solution:

// Creates the json object which will manage the information received
GsonBuilder builder = new GsonBuilder();


// Register an adapter to manage the date types as long values
builder.registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
return new Date(json.getAsJsonPrimitive().getAsLong());
}
});


Gson gson = builder.create();

I have the same problem when I tried to deserialize DateTime field with Rest client of Android annotations library. As a solution I've created custom GsonHttpMessageConverter

public class CustomGsonHttpMessageConverter extends GsonHttpMessageConverter {


public CustomGsonHttpMessageConverter() {
// Creates the json object which will manage the information received
GsonBuilder builder = new GsonBuilder();


// Register an adapter to manage the date types as long values
builder.registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
return new Date(json.getAsJsonPrimitive().getAsLong());
}
});


setGson(builder.create());
}
}

and define it in rest client

@Rest(rootUrl = "http://192.168.1.1:8080", converters = {CustomGsonHttpMessageConverter.class})
public interface RestClient extends RestClientErrorHandling {
...

I hope it will be helpful

I wrote an ImprovedDateTypeAdapter based on GSON default DateTypeAdapter that supports default dates format and the timestamp (long) format.

import com.google.gson.Gson;
import com.google.gson.JsonSyntaxException;
import com.google.gson.TypeAdapter;
import com.google.gson.TypeAdapterFactory;
import com.google.gson.reflect.TypeToken;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonToken;
import com.google.gson.stream.JsonWriter;


import java.io.IOException;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;
import java.util.Locale;
import java.util.TimeZone;


public final class ImprovedDateTypeAdapter extends TypeAdapter<Date> {


public static final TypeAdapterFactory FACTORY = new TypeAdapterFactory() {


public <T> TypeAdapter<T> create(Gson gson, TypeToken<T> typeToken) {


@SuppressWarnings("unchecked")
TypeAdapter<T> typeAdapter = (TypeAdapter<T>) ((typeToken.getRawType() == Date.class) ? new ImprovedDateTypeAdapter()
: null);
return typeAdapter;
}
};
private final DateFormat enUsFormat;
private final DateFormat localFormat;
private final DateFormat iso8601Format;


public ImprovedDateTypeAdapter() {
this.enUsFormat = DateFormat.getDateTimeInstance(2, 2, Locale.US);


this.localFormat = DateFormat.getDateTimeInstance(2, 2);


this.iso8601Format = buildIso8601Format();
}


private static DateFormat buildIso8601Format() {
DateFormat iso8601Format = new SimpleDateFormat(
"yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.US);
iso8601Format.setTimeZone(TimeZone.getTimeZone("UTC"));
return iso8601Format;
}


public Date read(JsonReader in) throws IOException {
if (in.peek() == JsonToken.NULL) {
in.nextNull();
return null;
}
return deserializeToDate(in.nextString());
}


private synchronized Date deserializeToDate(String json) {
try {


return new Date(Long.parseLong(json));
} catch (Exception e) {


try {


return this.localFormat.parse(json);
} catch (ParseException e1) {


try {


return this.enUsFormat.parse(json);
} catch (ParseException e2) {


try {


return this.iso8601Format.parse(json);
} catch (ParseException e3) {


throw new JsonSyntaxException(json, e3);
}
}
}
}
}


public synchronized void write(JsonWriter out, Date value)
throws IOException {
if (value == null) {
out.nullValue();
return;
}
String dateFormatAsString = this.enUsFormat.format(value);
out.value(dateFormatAsString);
}
}

To use it:

// Creates the json object which will manage the information received
GsonBuilder builder = new GsonBuilder();


// Register an adapter to manage the date types as long values
builder.registerTypeAdapter(Date.class, new ImprovedDateTypeAdapter());


Gson gson = builder.create();

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


JsonDeserializer<Date> deserializer= 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, serializer)
.registerTypeAdapter(Date.class, deserializer).create();

Use below snippet for converting milliseconds to Date while processing JSON.

    GsonBuilder gsonBuilder = new GsonBuilder();
// Adapter to convert long values to date types
gsonBuilder.registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {
public Date deserialize(JsonElement jsonElement, Type typeOfObj, JsonDeserializationContext context)
throws JsonParseException {
//Converting milliseconds to current Date. (instead of 1970)
return new Date(jsonElement.getAsLong() * 1000);
}
});
Gson gson = gsonBuilder.setPrettyPrinting().create();

For some reason I had compilation errors in Intellij with the above code using an anonymous class; a lambda worked for me:

private static Gson buildGson(){
// Deserialize longs as Dates
final JsonDeserializer<Date> dateDeserializer = (json, type, context) -> json == null ? null : new Date(json.getAsLong());
return new GsonBuilder().registerTypeAdapter(Date.class, dateDeserializer).create();
}

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializer;
import java.sql.Timestamp;
        

        

Gson gson = new GsonBuilder().registerTypeAdapter(Timestamp.class, (JsonDeserializer) (json, typeOfT, context) -> {
return new Timestamp(json.getAsLong());
}).create();