Java Gson parse not deserializing correctly

Question

I have a List<List<Integer>> with value

[[537316070],[306297332],[319303159],[538639811],[528406093],[166705854],[124574525],[967403337],[569514785],[304831454],[219384921],[308948513],[355538394],[297996417]]

after serializing it with Gson.

When I deserialize it using

List<List<Integer>> data = (List<List<Integer>>) GsonParser.gson.fromJson(datastr, List.class);

I am getting

[[5.3731607E8], [3.06297332E8], [3.19303159E8], [5.38639811E8], [5.28406093E8], [1.66705854E8], [1.24574525E8], [9.67403337E8], [5.69514785E8], [3.04831454E8], [2.19384921E8], [3.08948513E8], [3.55538394E8], [2.97996417E8]]

Does anyone know whats wrong?

Thanks

Answer 1

Gson , by default, parses any JSON number into a double . This happens in the ObjectTypeAdapter#read(JsonReader) method:

...
case NUMBER:
  return in.nextDouble();
...

Do the following

List<List<Integer>> data = GsonParser.gson.fromJson(json, new TypeToken<List<List<Integer>>>() {}.getType());

to get them as Integer instances.

The TypeToken is a Java hack to get the actual generic parameter types. The javadoc states

Constructs a new type literal. Derives represented class from type parameter.

Clients create an empty anonymous subclass. Doing so embeds the type parameter in the anonymous class's type hierarchy so we can reconstitute it at runtime despite erasure.