Gson and deserializing an array of objects with arrays in it.

Question

I am trying to use Gson to deserialize a json string returned from my webservice

The structure would be returned as TypeDTO[].

where TypeDTO is like

int id;
String name;
ArrayList<ItemDTO> items[] 

and ItemDTO is like

int id;
String name;
Boolean valid;

When I call the code as follows

Gson gson = new Gson();
TypeDTO[] mytypes = (TypeDTO[]) gson.fromJson(reply, TypeDTO[].class);

Everything inside the objects is null

However, If I use the

JSONArray and JSONObject to pull them out piece by piece from the org.json jars, it works fine and the fields are populated accordingly.

Any ideas as to what I'm doing wrong? is Gson extremely fast? Or am I better to stick with what I've got working already?

Thanks, David