GsonRequest a Volley adapter for JSON requests using Google Gson Lib

GsonRequest.java

public class GsonRequest<T> extends Request<T> {

    private Gson gson = new Gson();
    private Class<T> model;

    private Map<String, String> params;
    private Map<String, String> headers;
    private Listener listener;

    public GsonRequest(int method, String url, Class<T> model, Map<String, String> params, Map<String, String> headers,
                          Listener<T> listener, ErrorListener errorListener) {
        super(method, url, errorListener);

        this.model = model;
        this.params = (params != null) ? params : new HashMap<String, String>();
        this.headers = (headers != null) ? headers : new HashMap<String, String>();
        this.listener = listener;
    }

    public GsonRequest(int method, String url, Class<T> model, Map<String, String> params,
                       Listener<T> listener, ErrorListener errorListener) {
        super(method, url, errorListener);

        this.model = model;
        this.params = (params != null) ? params : new HashMap<String, String>();
        this.headers = new HashMap<String, String>();
        this.listener = listener;
    }

    public GsonRequest(int method, String url, Class<T> model, Listener<T> listener, ErrorListener errorListener) {
        super(method, url, errorListener);

        this.model = model;
        this.params = new HashMap<String, String>();
        this.headers = new HashMap<String, String>();
        this.listener = listener;
    }

    @Override
    public Map<String, String> getParams() throws AuthFailureError {
        return params ;
    }

    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        return headers;
    }

    @Override
    public byte[] getBody() throws AuthFailureError {
        Map<String, String> params = this.getParams();
        if (params != null && params.size() > 0) {
            return encodeParameters(params, getParamsEncoding());
        }
        return null;
    }

    private byte[] encodeParameters(Map<String, String> params, String paramsEncoding) {
        StringBuilder encodedParams = new StringBuilder();
        try {
            for (Map.Entry<String, String> entry : params.entrySet()) {
                encodedParams.append(URLEncoder.encode(entry.getKey(), paramsEncoding));
                encodedParams.append('=');
                encodedParams.append(URLEncoder.encode(entry.getValue(), paramsEncoding));
                encodedParams.append('&');
            }
            return encodedParams.toString().getBytes(paramsEncoding);
        } catch (UnsupportedEncodingException uee) {
            throw new RuntimeException("Encoding not supported: " + paramsEncoding, uee);
        }
    }
    @Override
    protected void deliverResponse(T response) {
        this.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, model),
                    HttpHeaderParser.parseCacheHeaders(response));
        } catch (UnsupportedEncodingException e) {
            return Response.error(new ParseError(e));
        } catch (JsonSyntaxException e) {
            return Response.error(new ParseError(e));
        }
    }
}