Android Volley custom header

Question

I am a beginner in android and I am trying to make an HTTP GET request, which returns PDF data. I am using Volley custom request, But it's not working. I am not able to set the header "Accept": "application/pdf". It's going to onErrorResponse.

Thank you.

I took the code from the below link;

Is it possible to download any file (pdf or zip) using volley on android?

class InputStreamVolleyRequest extends Request<byte[]> {
private final Response.Listener<byte[]> mListener;
private Map<String, String> mParams;

//create a static map for directly accessing headers
public Map<String, String> responseHeaders ;

public InputStreamVolleyRequest(int method, String mUrl ,Response.Listener<byte[]> listener,
                                Response.ErrorListener errorListener, HashMap<String, String> params) {
  // TODO Auto-generated constructor stub

    super(method, mUrl, errorListener);
     // this request would never use cache.
     setShouldCache(false);
     mListener = listener;
     mParams=params;
}

@Override
protected Map<String, String> getParams()
     throws com.android.volley.AuthFailureError {
  return mParams;
};


@Override
protected void deliverResponse(byte[] response) {
    mListener.onResponse(response);
}

@Override
protected Response<byte[]> parseNetworkResponse(NetworkResponse response) {

    //Initialise local responseHeaders map with response headers received
    responseHeaders = response.headers;

    //Pass the response data here
    return Response.success( response.data, HttpHeaderParser.parseCacheHeaders(response));
}
}

Main Activity:

public class MainActivity extends AppCompatActivity {



    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        String mUrl=
                "https://fhir-open.cerner.com/dstu2/ec2458f2-1e24-41c8-b71b-0e701af7583d/Binary/XR-197198634";
        InputStreamVolleyRequest request = new     InputStreamVolleyRequest(Request.Method.GET, mUrl,
                new Response.Listener<byte[]>() {
                    @Override
                    public void onResponse(byte[] response) {
                        // TODO handle the response
                        try {
                            if (response!=null) {

                                FileOutputStream outputStream;
                                String name="abc.pdf";
                                outputStream = openFileOutput(name, Context.MODE_PRIVATE);
                                outputStream.write(response);
                                outputStream.close();
                                Toast.makeText(MainActivity.this, "Download complete.", Toast.LENGTH_LONG).show();
                            }
                        } catch (Exception e) {
                            // TODO Auto-generated catch block
                            Log.d("KEY_ERROR", "UNABLE TO DOWNLOAD FILE");
                            e.printStackTrace();
                        }
                    }
                } ,new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                Log.d("KEY_ERROR1", "NOT WORKING");
                error.printStackTrace();
            }
        }, null);
        RequestQueue mRequestQueue = Volley.newRequestQueue(getApplicationContext(), new HurlStack());
        mRequestQueue.add(request);

    }
}