Generic Gson Deserializer and raw data GSON parser.

BaseService.java

/*
 * This class assumes that you use both RXJava and Dagger 2 in your project
 * 
 */

public abstract class BaseLocalService<T> {

    protected ResourceProvider mResourceProvider;
    protected Gson mGson;

    // ResourceProvider is a helper class that we use to retrieve resources,
    // eliminating the need to use Context in this class
    public BaseLocalService(ResourceProvider resourceProvider, Gson gson) {
        mResourceProvider = resourceProvider;
        mGson = gson;
    }

    // with this method
    public abstract Class<T> objectClass();
  
    protected T getObjectFromJson(int id) throws IllegalAccessException, InstantiationException, NotFoundException, IOException {
        String json = mResourceProvider.getRawJson(id);
        return mGson.fromJson(json, objectClass());
    }

    protected List<T> getLisOfObjectsFromJson(int id) throws IllegalAccessException, InstantiationException, NotFoundException, IOException {
        String json = mResourceProvider.getRawJson(id);
        
        return mGson.fromJson(json, TypeToken.getParameterized(ArrayList.class, objectClass()).getType());
    }
}

Example.java

/*
 * This example class shows us how to use the generic GSON deserializer
 */

public class ExampleService extends BaseLocalService<ExampleModel> {

    @Inject
    public AlertsLocalService(ResourceProvider resourceProvider, Gson gson) {
        super(resourceProvider, gson);
    }

    // This method is needed to retrieve the object class
    @Override
    public Class<ExampleModel> objectClass() {
        return ExampleModel.class;
    }

    public Single<List<ExampleModel>> getListOfAlerts() {
        try {
            return Single.just(getLisOfObjectsFromJson(R.raw.example));
        } catch (Exception | NotFoundException nfe ) {
            return Single.error(nfe);
        }
    }
}

ResourceProvider.java

/* 
 * This helper class will help us retrieve the local raw json stored in a file.
 */

public class ResourceProvider {

    private final Context mContext;

    public String getRawJson(@RawRes int id) throws Resources.NotFoundException, IOException {
        BufferedReader r = new BufferedReader(new InputStreamReader(mContext.getResources().openRawResource(id)));
        StringBuilder total = new StringBuilder();
        String line;
        while ((line = r.readLine()) != null) {
            total.append(line).append('\n');
        }
        return total.toString();
    }
}