Manually parse part of a response when using Retrofit

Question

I'm working with a REST API that returns a JSON document that starts as follows and includes a "collection" of items with string IDs like "ABC". Note the "routes" field, which contains a series of fields called "ABC", "ABD", "ABE" etc, however routes is not represented as an array in the json, so all these

{
"status":true,
"page":1,
"per_page":500,
"total_count":1234,
"total_pages":8,
"total_on_page":500,
"routes":{
    "ABC":[
    {
        "value":22313,
        <......>

I'm using Retrofit and the problem is the routes field is not an array (despite the fact conceptually it certainly is) and Retrofit/Gson require me to create a model object for routes with field vars abc, abd, etc - this is not practical as the data changes. For various reasons changing the server API is hard, so I'm looking to work around this on the Android client.

I figure these are options:

• Intercept the JSON document before it reaches Gson and tweak the document, possibly with a customised Gson parser, or by intercepting the HTTP response.

• Bypass the JSON parsing, and acquire the JSON document from Retrofit (I've yet to figure out how to do this, or if it's possible)

• Use some feature of Retrofit I'm unaware of to map field names to a collection.

I'd appreciate help, especially if there's a quick and easy way to resolve this.

Answer 1

It turns out that Retrofit's use of Gson by default makes it fairly easy to add a custom deserialiser to handle the portion of the JSON document that was the problem.

RestAdapter restAdapter = new RestAdapter.Builder()
        .setEndpoint(ApiDefinition.BASE_URL)
        .setConverter(getGsonConverter())
        .build();

public Converter getGsonConverter() {
    Gson gson = new GsonBuilder()
            .registerTypeAdapter(RouteList.class, new RouteTypeAdapter())
            .create();
    return  new GsonConverter(gson);
}


public class RouteTypeAdapter implements JsonDeserializer<RouteList> {
    @Override
    public RouteList deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
        Gson gson = new Gson();
        RouteList routeList = new RouteList();
        JsonObject jsonObject = json.getAsJsonObject();
        for (Map.Entry<String,JsonElement> elementJson : jsonObject.entrySet()){
            RouteList wardsRoutes = gson.fromJson(elementJson.getValue().getAsJsonArray(), RouteList.class);
            routeList.addAll(wardsRoutes);
        }
        return routeList;
    }

}