android - Pass Parameter with Volley POST

Question

I was able to call an HTTP endpoint using Postman and these parameters:

{
    "name":"Val",
    "subject":"Test"
}

However I am unable to do the same with Volley through Android: Here is trying to use JSONRequest:

HashMap<String, String> params2 = new HashMap<String, String>();
        params.put("name", "Val");
        params.put("subject", "Test Subject");

        JsonObjectRequest jsObjRequest = new JsonObjectRequest
                (Request.Method.POST, Constants.CLOUD_URL, new JSONObject(params2), new Response.Listener<JSONObject>() {

                    @Override
                    public void onResponse(JSONObject response) {
                        mView.showMessage("Response: " + response.toString());
                    }
                }, new Response.ErrorListener() {

                    @Override
                    public void onErrorResponse(VolleyError error) {
                        // TODO Auto-generated method stub
                        mView.showMessage(error.getMessage());

                    }
                });

        // Access the RequestQueue through your singleton class.
        VolleySingleton.getInstance(mContext).addToRequestQueue(jsObjRequest);

And here is trying StringRequest

private void postMessage(Context context, final String name, final String subject ){

        RequestQueue queue = Volley.newRequestQueue(context);
        StringRequest sr = new StringRequest(Request.Method.POST, Constants.CLOUD_URL, new Response.Listener<String>() {
            @Override
            public void onResponse(String response) {
                mView.showMessage(response);
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {

            }
        }){
            @Override
            protected Map<String,String> getParams(){
                Map<String,String> params = new HashMap<String, String>();
                params.put("name", name);
                params.put("subject", subject);

                return params;
            }

            @Override
            public Map<String, String> getHeaders() throws AuthFailureError {
                Map<String,String> params = new HashMap<String, String>();
                params.put("Content-Type","application/x-www-form-urlencoded");
                return params;
            }
        };
        queue.add(sr);
    }

When I use JSONRequest, the call POSTs but no parameter is passed and when I use StringRequest I get the error below? How can I pass JSON data to Volley call?

E/Volley: [13053] BasicNetwork.performRequest: Unexpected response code 400 for 

Here is the server code that handles the request

public static async Task<HttpResponseMessage> Run(HttpRequestMessage req, TraceWriter log)
{
    var helloRequest = await req.Content.ReadAsAsync<HelloRequest>();

    var name = helloRequest?.Name ?? "world";    
    var responseMessage = $"Hello {personToGreet}!";


    log.Info($"Message: {responseMessage}");


    return req.CreateResponse(HttpStatusCode.OK, $"All went well.");
}

public class HelloRequest
{
    public string Name { get; set; }
    public string Subject { get; set; }
}

Answer 1

The server code is expecting a JSON object is returning string or rather Json string.

JsonObjectRequest

JSONRequest sends a JSON object in the request body and expects a JSON object in the response. Since the server returns a string it ends up throwing ParseError

StringRequest

StringRequest sends a request with body type x-www-form-urlencoded but since the server is expecting a JSON object. You end up getting 400 Bad Request

The Solution

The Solution is to change the content-type in the string request to JSON and also pass a JSON object in the body. Since it already expects a string you response you are good there. Code for that should be as follows.

StringRequest sr = new StringRequest(Request.Method.POST, Constants.CLOUD_URL, new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        mView.showMessage(response);
    }
}, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        mView.showMessage(error.getMessage());
    }
}) {
    @Override
    public byte[] getBody() throws AuthFailureError {
        HashMap<String, String> params2 = new HashMap<String, String>();
        params2.put("name", "Val");
        params2.put("subject", "Test Subject");
        return new JSONObject(params2).toString().getBytes();
    }

    @Override
    public String getBodyContentType() {
        return "application/json";
    }
};

Also there is a bug here in the server code

var responseMessage = $"Hello {personToGreet}!";

Should be

var responseMessage = $"Hello {name}!";