Handle an empty response in a JSONRequest with Volley

Question

I'm using Volley to make a POST request in my application, and in my case, a good response is a 201 with an empty body. I'm using a JSONRequest, to make the call.

My problem is that the error response handler is getting called because response is empty.

Below is my request:

    Request request = new JsonRequest<Object>(Request.Method.POST, url, body, new Response.Listener<Object>() {

        @Override
        public void onResponse(Object response) {

        }
    }, new ErrorListener(context)) {

        @Override
        protected Response<Object> parseNetworkResponse(NetworkResponse response) {

            Log.d(TAG, "success!!!!!!");
            if (response.statusCode == 201)
                mListener.resetPasswordWasSent();
            return null;
        }

        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            Map<String,String> params = new HashMap<String, String>();
            params.put("Content-Type","application/json");
            params.put("Accept", "application/json");
            return params;
        }
    };

    requestQueue.add(request);

My parseNetworkResponse function is getting called, then the ErrorListener, and the onResponse method never gets hits because I get a NullPointerException in the ErrorListener.

I can ignore the NullPointerException in my error listener, but I'd prefer not to. Obviously, I can simply send my callback in the parseNetworkResponse, but I don't want to have any errors popping up.

Anyone know how I should handle this?

Edit: Here is the stacktrace:

05-06 09:44:19.586  27546-27560/com.threepoundhealth.euco E/Volley﹕ [1830] NetworkDispatcher.run: Unhandled exception java.lang.NullPointerException
    java.lang.NullPointerException
    at com.android.volley.NetworkDispatcher.run(NetworkDispatcher.java:126)

Samoyed

Where exactly do you get the NullPointerException? Inside the Lib or in your code? please add the StackTrace. – Deictic

@Deictic please see the edits – Samoyed

I have this issue too, my onError is never called – Ramonramona

@Ramonramona my onError is getting called - my onResponse is not getting called – Samoyed

Have you initialized mListener? – Radicle

@AtulOHolic yes. My resetPasswordWasSent() is getting called – Samoyed

Can you paste this method - resetPasswordWasSent() – Radicle

Answer 1

You could try to hack like this. Create a JsonObjectRequest subclass, override the parseNetworkResponse method and check the response data, if it is an empty byte[], replace the data with byte[] representation of a empty json {}.

public class VolleyJsonRequest extends JsonObjectRequest {

    ...

    @Override
    protected Response<JSONObject> parseNetworkResponse(NetworkResponse response) {
        try {
            if (response.data.length == 0) {
                byte[] responseData = "{}".getBytes("UTF8");
                response = new NetworkResponse(response.statusCode, responseData, response.headers, response.notModified);
            }
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }
        return super.parseNetworkResponse(response);
    }    
}

Ekaterinoslav

Great answer! That NetworkResponse constructor however, has been deprecated. For convenience, I write the new one: response = new NetworkResponse(response.statusCode, responseData, response.notModified, response.networkTimeMs, response.allHeaders); – Maeganmaelstrom

Answer 2

You can use a StringRequest. Your listener will be called with an empty String "".

Klondike

I'd like to be able to send JSON though, and not use the 'getParams' method where I'd have to create a map of the params – Samoyed

Using JsonRequest and JsonBodyRequest appears to give an error on an empty response. I'd imagine thats a bug but it seems like StringRequest is only way to handle an empty response without triggering the errorListener. – Klondike

Answer 3

If no response is expected, then JsonRequest can be extended with that in mind.

An example in Kotlin:

/**
 * A request containing a [JSONObject] body for a given URL, expecting an empty response.
 */
class JsonObjectRequestEmptyResponse
/**
 * Creates a new request.
 * @param method the HTTP method to use
 * @param url URL to fetch the JSON from
 * @param jsonRequest A [JSONObject] to post with the request.
 * @param listener Listener to receive a successful response
 * @param errorListener Error listener, or null to ignore errors.
 */
(method: Int, url: String, jsonRequest: JSONObject,
 listener: () -> Unit, errorListener: ErrorListener?) : JsonRequest<Unit>(method, url,
        jsonRequest.toString(), Listener<Unit> { _response -> listener() }, errorListener) {

    override fun parseNetworkResponse(response: NetworkResponse): Response<Unit> {
        if (response.data.isEmpty()) {
            return Response.success(Unit,
                    HttpHeaderParser.parseCacheHeaders(response))
        } else {
            return Response.error(VolleyError("unexpected data"))
        }
    }
}

Prescriptive

Answer 4

I got the same problem and developed a global solution to handle it (and few lack of functionality of Volley), I posted it on another thread but I think it can help many people which are looking for a solution to your problem.

  /**
  * Created by laurentmeyer on 25/07/15.
  */
 public class GenericRequest<T> extends JsonRequest<T> {

     private final Gson gson = new Gson();
     private final Class<T> clazz;
     private final Map<String, String> headers;
     // Used for request which do not return anything from the server
     private boolean muteRequest = false;

     /**
      * Basically, this is the constructor which is called by the others.
      * It allows you to send an object of type A to the server and expect a JSON representing a object of type B.
      * The problem with the #JsonObjectRequest is that you expect a JSON at the end.
      * We can do better than that, we can directly receive our POJO.
      * That's what this class does.
      *
      * @param method:        HTTP Method
      * @param classtype:     Classtype to parse the JSON coming from the server
      * @param url:           url to be called
      * @param requestBody:   The body being sent
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      * @param headers:       Added headers
      */
     private GenericRequest(int method, Class<T> classtype, String url, String requestBody,
                           Response.Listener<T> listener, Response.ErrorListener errorListener, Map<String, String> headers) {
         super(method, url, requestBody, listener,
                 errorListener);
         clazz = classtype;
         this.headers = headers;
         configureRequest();
     }

     /**
      * Method to be called if you want to send some objects to your server via body in JSON of the request (with headers and not muted)
      *
      * @param method:        HTTP Method
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param toBeSent:      Object which will be transformed in JSON via Gson and sent to the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      * @param headers:       Added headers
      */
     public GenericRequest(int method, String url, Class<T> classtype, Object toBeSent,
                           Response.Listener<T> listener, Response.ErrorListener errorListener, Map<String, String> headers) {
         this(method, classtype, url, new Gson().toJson(toBeSent), listener,
                 errorListener, headers);
     }

     /**
      * Method to be called if you want to send some objects to your server via body in JSON of the request (without header and not muted)
      *
      * @param method:        HTTP Method
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param toBeSent:      Object which will be transformed in JSON via Gson and sent to the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      */
     public GenericRequest(int method, String url, Class<T> classtype, Object toBeSent,
                           Response.Listener<T> listener, Response.ErrorListener errorListener) {
         this(method, classtype, url, new Gson().toJson(toBeSent), listener,
                 errorListener, new HashMap<String, String>());
     }

     /**
      * Method to be called if you want to send something to the server but not with a JSON, just with a defined String (without header and not muted)
      *
      * @param method:        HTTP Method
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param requestBody:   String to be sent to the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      */
     public GenericRequest(int method, String url, Class<T> classtype, String requestBody,
                           Response.Listener<T> listener, Response.ErrorListener errorListener) {
         this(method, classtype, url, requestBody, listener,
                 errorListener, new HashMap<String, String>());
     }

     /**
      * Method to be called if you want to GET something from the server and receive the POJO directly after the call (no JSON). (Without header)
      *
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      */
     public GenericRequest(String url, Class<T> classtype, Response.Listener<T> listener, Response.ErrorListener errorListener) {
         this(Request.Method.GET, url, classtype, "", listener, errorListener);
     }

     /**
      * Method to be called if you want to GET something from the server and receive the POJO directly after the call (no JSON). (With headers)
      *
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      * @param headers:       Added headers
      */
     public GenericRequest(String url, Class<T> classtype, Response.Listener<T> listener, Response.ErrorListener errorListener, Map<String, String> headers) {
         this(Request.Method.GET, classtype, url, "", listener, errorListener, headers);
     }

     /**
      * Method to be called if you want to send some objects to your server via body in JSON of the request (with headers and muted)
      *
      * @param method:        HTTP Method
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param toBeSent:      Object which will be transformed in JSON via Gson and sent to the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      * @param headers:       Added headers
      * @param mute:          Muted (put it to true, to make sense)
      */
     public GenericRequest(int method, String url, Class<T> classtype, Object toBeSent,
                           Response.Listener<T> listener, Response.ErrorListener errorListener, Map<String, String> headers, boolean mute) {
         this(method, classtype, url, new Gson().toJson(toBeSent), listener,
                 errorListener, headers);
         this.muteRequest = mute;
     }

     /**
      * Method to be called if you want to send some objects to your server via body in JSON of the request (without header and muted)
      *
      * @param method:        HTTP Method
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param toBeSent:      Object which will be transformed in JSON via Gson and sent to the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      * @param mute:          Muted (put it to true, to make sense)
      */
     public GenericRequest(int method, String url, Class<T> classtype, Object toBeSent,
                           Response.Listener<T> listener, Response.ErrorListener errorListener, boolean mute) {
         this(method, classtype, url, new Gson().toJson(toBeSent), listener,
                 errorListener, new HashMap<String, String>());
         this.muteRequest = mute;

     }

     /**
      * Method to be called if you want to send something to the server but not with a JSON, just with a defined String (without header and not muted)
      *
      * @param method:        HTTP Method
      * @param url:           URL to be called
      * @param classtype:     Classtype to parse the JSON returned from the server
      * @param requestBody:   String to be sent to the server
      * @param listener:      Listener of the request
      * @param errorListener: Error handler of the request
      * @param mute:          Muted (put it to true, to make sense)
      */
     public GenericRequest(int method, String url, Class<T> classtype, String requestBody,
                           Response.Listener<T> listener, Response.ErrorListener errorListener, boolean mute) {
         this(method, classtype, url, requestBody, listener,
                 errorListener, new HashMap<String, String>());
         this.muteRequest = mute;

     }


     @Override
     protected Response<T> parseNetworkResponse(NetworkResponse response) {
         // The magic of the mute request happens here
         if (muteRequest) {
             if (response.statusCode >= 200 && response.statusCode <= 299) {
                 // If the status is correct, we return a success but with a null object, because the server didn't return anything
                 return Response.success(null, HttpHeaderParser.parseCacheHeaders(response));
             }
         } else {
             try {
                 // If it's not muted; we just need to create our POJO from the returned JSON and handle correctly the errors
                 String json = new String(response.data, HttpHeaderParser.parseCharset(response.headers));
                 T parsedObject = gson.fromJson(json, clazz);
                 return Response.success(parsedObject, HttpHeaderParser.parseCacheHeaders(response));
             } catch (UnsupportedEncodingException e) {
                 return Response.error(new ParseError(e));
             } catch (JsonSyntaxException e) {
                 return Response.error(new ParseError(e));
             }
         }
         return null;
     }

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

     private void configureRequest() {
         // Set retry policy
         // Add headers, for auth for example
         // ...
     }
 }

Here is the original answer on the other thread.

Abstraction