Java – How to resolve Android Volley gson requests to object lists/collections

How to resolve Android Volley gson requests to object lists/collections… here is a solution to the problem.

How to resolve Android Volley gson requests to object lists/collections

I’m trying to make a gson request using android volley. At the moment it is working fine and I am happy. But why do I try to get a List<> or object collection, my code no longer works.

Current code:

public class ReviewModel 
{
  public long Id;
  public Strring Description;
}

Here’s how I use my gson class:

    GsonRequest<ReviewModel> jsObjRequest = new GsonRequest<ReviewModel>(Request.Method.GET,
            url, ReviewModel.class, new Response.Listener<ReviewModel>() {
                @Override
                public void onResponse(ReviewModel response) {
                    ReviewsHandleOkResponse(response);
                }

}, new ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    ReviewsHandleErrorResponse(error);
                }
            });
    Network.getInstance(getActivity()).addToRequestQueue(jsObjRequest);
}

Here is my Volley GSON request class:

public class GsonRequest<T> extends Request<T> {
private final Gson gson = new Gson();
private final Class<T> clazz;
private final Map<String, String> headers;
private final Map<String, String> params;
private final Listener<T> listener;

/**
 * Make a GET request and return a parsed object from JSON.
 * 
 * @param url
 *            URL of the request to make
 * @param clazz
 *            Relevant class object, for Gson's reflection
 * @param headers
 *            Map of request headers
 */
public GsonRequest(int method, String url, Class<T> clazz,
        Map<String, String> headers, Map<String, String> params,
        Listener<T> listener, ErrorListener errorListener) {
    super(method, Network.getFullUrl(url), errorListener);
    this.clazz = clazz;
    this.headers = headers;
    this.params = params;
    this.listener = listener;
}

/**
 * Recieves header
 * 
 * @param method
 * @param url
 * @param clazz
 * @param params
 * @param listener
 * @param errorListener
 */
public GsonRequest(int method, String url, Class<T> clazz,
        Map<String, String> params, Listener<T> listener,
        ErrorListener errorListener) {
    super(method, Network.getFullUrl(url), errorListener);
    this.clazz = clazz;
    this.headers = new HashMap<String, String>();
    this.params = params;
    this.listener = listener;
}

/**
 * No params or headers
 * 
 * @param method
 * @param url
 * @param clazz
 * @param listener
 * @param errorListener
 */
public GsonRequest(int method, String url, Class<T> clazz,
        Listener<T> listener, ErrorListener errorListener) {
    super(method, Network.getFullUrl(url), errorListener);
    this.clazz = clazz;
    this.headers = new HashMap<String, String>();
    this.params = new HashMap<String, String>();
    this.listener = listener;
}

@Override
public Map<String, String> getHeaders() throws AuthFailureError {
    return headers != null ? headers : super.getHeaders();
}

@Override
public Map<String, String> getParams() throws AuthFailureError {
    return params != null ? params : super.getParams();
}

@Override
protected void deliverResponse(T response) {
    listener.onResponse(response);
}

@Override
protected Response<T> parseNetworkResponse(NetworkResponse response) {
    try {
        String json = new String(response.data,
                HttpHeaderParser.parseCharset(response.headers));
        return Response.success(gson.fromJson(json, clazz),
                HttpHeaderParser.parseCacheHeaders(response));
    } catch (UnsupportedEncodingException e) {
        return Response.error(new ParseError(e));
    } catch (JsonSyntaxException e) {
        return Response.error(new ParseError(e));
    }
  }
}

However, when I parse it to List<ReviewModel> I get a compilation error.

Based on my research, I need to do something:

Type collectionType = new TypeToken<ArrayList<ReviewModel>>(){}.getType();      
     api/v1/reviews/products/{productId}/{pageNumber}/{pageSize}
    String url = "api/v1/reviews/products/" + productId + "/" + currentPage + "/" + pageSize;
    GsonRequest<ArrayList<ReviewModel>> jsObjRequest = new GsonRequest<ArrayList<ReviewModel>>(Request.Method.GET,
            url, (Class<ArrayList<ReviewModel>>) collectionType, new Response.Listener<ArrayList<ReviewModel>>() {
                @Override
                public void onResponse(ArrayList<ReviewModel> response) {
                    ReviewsHandleOkResponse(response);
                }

}, new ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    ReviewsHandleErrorResponse(error);
                }
            });
    Network.getInstance(getActivity()).addToRequestQueue(jsObjRequest);
}

But this gives me the following error:

10-28 21:12:59.940: E/AndroidRuntime(28564):
java.lang.RuntimeException: Unable to start activity
ComponentInfo{com.menu/com.menu.activities.ProductViewActivity}:
java.lang.ClassCastException:
com.google.gson.internal.$Gson$Types$ParameterizedTypeImpl cannot be
cast to java.lang.Class

Do I need to modify my GsonRequest class and add another constructor that doesn’t take the type class?

Solution

Use YourClass[] as the list of objects in the Volley request. It solved my problem. The following code should help you:

GsonRequest<ReviewModel[]> jsObjRequest = new GsonRequest<ReviewModel[]>(Request.Method.GET,
        url, ReviewModel[].class, new Response.Listener<ReviewModel[]>() {
            @Override
            public void onResponse(ReviewModel[] response) {
                ReviewsHandleOkResponse(response);
            }
        }, new ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                ReviewsHandleErrorResponse(error);
            }
        });
Network.getInstance(getActivity()).addToRequestQueue(jsObjRequest);
}

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