Applicaton.java

    RequestQueue req;
    ImageLoader.ImageCache imageCache;
    ImageLoader imageLoader;
    final int DEFAULT_CACHE_SIZE = 16 * 1024 * 1024; // for DiskBasedCache
    private static final String DEFAULT_CACHE_DIR = "volley";

    private void createImageLoader() {
        if (imageCache == null) {
            imageCache = new BitmapLruCache();
            imageLoader = new ImageLoader(Volley.newRequestQueue(this), imageCache);
        }
    }

    public ImageLoader getImageLoader() {
        return imageLoader;
    }

    /**
     * If RequestQueue is null, create one with {@code cacheSize} amount of cache
     */
    public RequestQueue getRequestQueue() {
        if (req == null) {
            req = Volley.newRequestQueue(this);
            File cacheDir = new File(this.getCacheDir(), DEFAULT_CACHE_DIR);
            DiskBasedCache cache = new DiskBasedCache(cacheDir, DEFAULT_CACHE_SIZE);
            req = new RequestQueue(cache, new BasicNetwork(new HurlStack()));
            req.start();
        }
        return req;
    }