public class InitApplication extends Application {

private RequestQueue queue;
private static InitApplication sInstance;

private static final String TAG = InitApplication.class.getSimpleName();


@Override
public void onCreate() {
    super.onCreate();

    sInstance = this;

    Stetho.initializeWithDefaults(this);

}

public static synchronized InitApplication getInstance() {
    return sInstance;
}

public <T> void addToQueue(Request<T> req, String tag) {
    req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
    getQueue().add(req);
}

public <T> void addToQueue(Request<T> req) {
    req.setTag(TAG);
    getQueue().add(req);
}

public void cancelPendingRequests(Object tag) {
    if (queue != null) {
        queue.cancelAll(tag);
    }
}

public RequestQueue getQueue() {
    if (queue == null) {
        queue = Volley.newRequestQueue(getApplicationContext());
        return queue;
    }
    return queue;
}
}

JsonObjectRequest myRequest = new JsonObjectRequest(Method.GET,
        url, null,
        new Response.Listener<JSONObject>() {

            @Override
            public void onResponse(JSONObject response) {
                Log.d(TAG, response.toString());
            }
        }, new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                Log.d(TAG, "Error: " + error.getMessage());
            }
});

myRequest.setRetryPolicy(new DefaultRetryPolicy(
        MY_SOCKET_TIMEOUT_MS, 
        DefaultRetryPolicy.DEFAULT_MAX_RETRIES, 
        DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));

final TextView mTextView = (TextView) findViewById(R.id.text);
...

// Instantiate the RequestQueue.
RequestQueue queue = Volley.newRequestQueue(this);
String url ="http://www.google.com";

// Request a string response from the provided URL.
StringRequest stringRequest = new StringRequest(Request.Method.GET, url,
            new Response.Listener<String>() {
    @Override
    public void onResponse(String response) {
        // Display the first 500 characters of the response string.
        mTextView.setText("Response is: "+ response.substring(0,500));
    }
}, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        mTextView.setText("That didn't work!");
    }
});
// Add the request to the RequestQueue.
queue.add(stringRequest);

<resources>
    <declare-styleable name="MoreNetworkImageView">
        <attr name="defaultImageResId" format="reference"/>
        <attr name="errorImageResId" format="reference"/>
    </declare-styleable>
</resources>

package my.namespace;

import android.content.Context;
import android.content.res.TypedArray;
import android.support.annotation.NonNull;
import android.util.AttributeSet;

import com.android.volley.toolbox.NetworkImageView;

public class MoreNetworkImageView extends NetworkImageView {
    public MoreNetworkImageView(@NonNull final Context context) {
        super(context);
    }

    public MoreNetworkImageView(@NonNull final Context context, @NonNull final AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public MoreNetworkImageView(@NonNull final Context context, @NonNull final AttributeSet attrs, final int defStyle) {
        super(context, attrs, defStyle);

        final TypedArray attributes = context.obtainStyledAttributes(attrs, R.styleable.MoreNetworkImageView, defStyle, 0);

        // load defaultImageResId from XML
        int defaultImageResId = attributes.getResourceId(R.styleable.MoreNetworkImageView_defaultImageResId, 0);
        if (defaultImageResId > 0) {
            setDefaultImageResId(defaultImageResId);
        }

        // load errorImageResId from XML
        int errorImageResId = attributes.getResourceId(R.styleable.MoreNetworkImageView_errorImageResId, 0);
        if (errorImageResId > 0) {
            setErrorImageResId(errorImageResId);
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.CardView
  xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:app="http://schemas.android.com/apk/res-auto"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="wrap_content"
  android:layout_height="fill_parent">

  <my.namespace.MoreNetworkImageView
    android:layout_width="64dp"
    android:layout_height="64dp"
    app:errorImageResId="@drawable/error_img"
    app:defaultImageResId="@drawable/default_img"
    tools:defaultImageResId="@drawable/editor_only_default_img"/>
    <!-- 
      Note: The "tools:" prefix does NOT work for custom attributes in Android Studio 2.1 and 
      older at least, so in this example the defaultImageResId would show "default_img" in the 
      editor, not the "editor_only_default_img" drawable even though it should if it was 
      supported as an editor-only override correctly like standard Android properties.
    -->

</android.support.v7.widget.CardView>

// assume a Request and RequestQueue have already been initialized somewhere above

public static final String TAG = "SomeTag";

// Set the tag on the request.
request.setTag(TAG);

// Add the request to the RequestQueue.
mRequestQueue.add(request);

// To cancel this specific request
request.cancel();

// ... then, in some future life cycle event, for example in onStop()
// To cancel all requests with the specified tag in RequestQueue
mRequestQueue.cancelAll(TAG);

final TextView mTxtDisplay = (TextView) findViewById(R.id.txtDisplay);
ImageView mImageView;
String url = "http://ip.jsontest.com/";

final JsonObjectRequest jsObjRequest = new JsonObjectRequest
        (Request.Method.GET, url, null, new Response.Listener<JSONObject>() {    
    @Override
    public void onResponse(JSONObject response) {
        mTxtDisplay.setText("Response: " + response.toString());
    }
}, new Response.ErrorListener() {    
    @Override
    public void onErrorResponse(VolleyError error) {
        // ...
    }
});

requestQueue.add(jsObjRequest);

new JsonObjectRequest(REQUEST_METHOD, REQUEST_URL, REQUEST_BODY, RESP_LISTENER, ERR_LISTENER) {
    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        HashMap<String, String> customHeaders = new Hashmap<>();

        customHeaders.put("KEY_0", "VALUE_0");
        ...
        customHeaders.put("KEY_N", "VALUE_N");

        return customHeaders;
    }
};

public class MyCustomRequest extends Request {
    ...
    @Override
    public Map<String, String> getHeaders() throws AuthFailureError {
        HashMap<String, String> customHeaders = new Hashmap<>();

        customHeaders.put("KEY_0", "VALUE_0");
        ...
        customHeaders.put("KEY_N", "VALUE_N");

        return customHeaders;
    }
    ...
}

// User input data.
String email = "[email protected]";
String password = "123";

// Our server URL for handling POST requests.
String URL = "http://my.server.com/login.php";

// When we create a StringRequest (or a JSONRequest) for sending
// data with Volley, we specify the Request Method as POST, and 
// the URL that will be receiving our data.
StringRequest stringRequest = 
    new StringRequest(Request.Method.POST, URL, 
    new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            // At this point, Volley has sent the data to your URL
            // and has a response back from it. I'm going to assume
            // that the server sends an "OK" string.
            if (response.equals("OK")) {
                // Do login stuff.
            } else {
                // So the server didn't return an "OK" response.
                // Depending on what you did to handle errors on your
                // server, you can decide what action to take here.
            }
        }
    },
    new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {      
            // This is when errors related to Volley happen.
            // It's up to you what to do if that should happen, but
            // it's usually not a good idea to be too clear as to
            // what happened here to your users.
        }
    }) {
        @Override
        protected Map<String, String> getParams() throws AuthFailureError {
            // Here is where we tell Volley what it should send in
            // our POST request. For this example, we want to send
            // both the email and the password. 
            
            // We will need key ids for our data, so our server can know
            // what is what.
            String key_email = "email";
            String key_password = "password";

            Map<String, String> map = new HashMap<String, String>();
            // map.put(key, value);
            map.put(key_email, email);
            map.put(key_password, password);
            return map;
        }
    };

    // This is a policy that we need to specify to tell Volley, what
    // to do if it gets a timeout, how many times to retry, etc.
    stringRequest.setRetryPolicy(new RetryPolicy() {
            @Override
            public int getCurrentTimeout() {
                // Here goes the timeout.
                // The number is in milliseconds, 5000 is usually enough,
                // but you can up or low that number to fit your needs.
                return 50000;
            }
            @Override
            public int getCurrentRetryCount() {
                // The maximum number of attempts.
                // Again, the number can be anything you need.
                return 50000;
            }
            @Override
            public void retry(VolleyError error) throws VolleyError {
                // Here you could check if the retry count has gotten
                // to the maximum number, and if so, send a VolleyError
                // message or similar. For the sake of the example, I'll 
                // show a Toast.  
                Toast.makeText(getContext(), error.toString(), Toast.LENGTH_LONG).show();
            }
    });
    
    // And finally, we create a Volley Queue. For this example, I'm using
    // getContext(), because I was working with a Fragment. But context could
    // be "this", "getContext()", etc.
    RequestQueue requestQueue = Volley.newRequestQueue(getContext());
    requestQueue.add(stringRequest);

} else { 
    // If, for example, the user inputs an email that is not currently
    // on your remote DB, here's where we can inform the user.
    Toast.makeText(getContext(), "Wrong email", Toast.LENGTH_LONG).show();
}

public class VolleyErrorHelper {
        /**
         * Returns appropriate message which is to be displayed to the user
         * against the specified error object.
         *
         * @param error
         * @param context
         * @return
         */

        public static String getMessage (Object error , Context context){
            if(error instanceof TimeoutError){
                return context.getResources().getString(R.string.timeout);
            }else if (isServerProblem(error)){
                return handleServerError(error ,context);

            }else if(isNetworkProblem(error)){
                return context.getResources().getString(R.string.nointernet);
            }
            return context.getResources().getString(R.string.generic_error);

        }

        private static String handleServerError(Object error, Context context) {

            VolleyError er = (VolleyError)error;
            NetworkResponse response = er.networkResponse;
            if(response != null){
                switch (response.statusCode){

                    case 404:
                    case 422:
                    case 401:
                        try {
                            // server might return error like this { "error": "Some error occured" }
                            // Use "Gson" to parse the result
                            HashMap<String, String> result = new Gson().fromJson(new String(response.data),
                                    new TypeToken<Map<String, String>>() {
                                    }.getType());

                            if (result != null && result.containsKey("error")) {
                                return result.get("error");
                            }

                        } catch (Exception e) {
                            e.printStackTrace();
                        }
                        // invalid request
                        return ((VolleyError) error).getMessage();

                    default:
                        return context.getResources().getString(R.string.timeout);
                }
            }

            return context.getResources().getString(R.string.generic_error);
        }

        private static boolean isServerProblem(Object error) {
            return (error instanceof ServerError || error instanceof AuthFailureError);
        }

        private static boolean isNetworkProblem (Object error){
            return (error instanceof NetworkError || error instanceof NoConnectionError);
        }

private final String PROTOCOL_CONTENT_TYPE = String.format("application/json; charset=%s", PROTOCOL_CHARSET);

    public BooleanRequest(int method, String url, String requestBody, Response.Listener<Boolean> listener, Response.ErrorListener errorListener) {
        super(method, url, errorListener);
        this.mListener = listener;
        this.mErrorListener = errorListener;
        this.mRequestBody = requestBody;
    }

    @Override
    protected Response<Boolean> parseNetworkResponse(NetworkResponse response) {
        Boolean parsed;
        try {
            parsed = Boolean.valueOf(new String(response.data, HttpHeaderParser.parseCharset(response.headers)));
        } catch (UnsupportedEncodingException e) {
            parsed = Boolean.valueOf(new String(response.data));
        }
        return Response.success(parsed, HttpHeaderParser.parseCacheHeaders(response));
    }

    @Override
    protected VolleyError parseNetworkError(VolleyError volleyError) {
        return super.parseNetworkError(volleyError);
    }

    @Override
    protected void deliverResponse(Boolean response) {
        mListener.onResponse(response);
    }

    @Override
    public void deliverError(VolleyError error) {
        mErrorListener.onErrorResponse(error);
    }

    @Override
    public String getBodyContentType() {
        return PROTOCOL_CONTENT_TYPE;
    }

    @Override
    public byte[] getBody() throws AuthFailureError {
        try {
            return mRequestBody == null ? null : mRequestBody.getBytes(PROTOCOL_CHARSET);
        } catch (UnsupportedEncodingException uee) {
            VolleyLog.wtf("Unsupported Encoding while trying to get the bytes of %s using %s",
                    mRequestBody, PROTOCOL_CHARSET);
            return null;
        }
    }
}

try {
        JSONObject jsonBody;
        jsonBody = new JSONObject();
        jsonBody.put("Title", "Android Demo");
        jsonBody.put("Author", "BNK");
        jsonBody.put("Date", "2015/08/28");
        String requestBody = jsonBody.toString();
        BooleanRequest booleanRequest = new BooleanRequest(0, url, requestBody, new Response.Listener<Boolean>() {
            @Override
            public void onResponse(Boolean response) {
                Toast.makeText(mContext, String.valueOf(response), Toast.LENGTH_SHORT).show();
            }
        }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
                Toast.makeText(mContext, error.toString(), Toast.LENGTH_SHORT).show();
            }
        });
        // Add the request to the RequestQueue.
        queue.add(booleanRequest);
    } catch (JSONException e) {
        e.printStackTrace();
    }

JSONArray requestBody = new JSONArray();

new JsonObjectRequest(Request.Method.POST, REQUEST_URL, null, RESP_LISTENER, ERR_LISTENER) {
    @Override
    public byte[] getBody() {
        try {
            return requestBody.toString().getBytes(PROTOCOL_CHARSET);
        } catch (UnsupportedEncodingException uee) {
            // error handling
            return null;
        }
    }
};

dependencies {
    ...
    compile 'com.android.volley:volley:1.0.0'
}

<uses-permission android:name="android.permission.INTERNET"/>