问Picasso图像缓存

EN

DownloadImage downloadImage = new DownloadImage(); 
downloadImage.execute(advert.getImgUrl());

private class DownloadImage extends AsyncTask<String, Void, Bitmap> {

    @Override
    protected Bitmap doInBackground(String... arg) {
        Bitmap bmp = null;
        try {
            URL url = new URL(arg[0]);
            bmp = BitmapFactory.decodeStream(url.openConnection()
                    .getInputStream());

        } catch (MalformedURLException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
            return null;
        }
        return bmp;

    }

    @Override
    protected void onPostExecute(Bitmap result) {
        if (result == null) {
            Intent intent = new Intent(AdvertisingActivity.this,
                    AdvertisingErrorActivity.class);
            intent.putExtra("ad-error", "Error downloading image");
        }
        adImg.setImageBitmap(result);
        super.onPostExecute(result);
    }
}