Copy files from Android's assets folder to external storage (We will put some defaults files in /Assets folder, copy to /data/data/PACKAGE_NAME/images folder at runtime. And later, if new files available, the app will download images and replace to data/data folder)

copyAssetsToSDCard.java

private void copyAssets() {
  AssetManager assetManager = getAssets();
  String[] files = null;
  try {
    files = assetManager.list("img"); 
  } catch (IOException e) {
      Log.e("tag", "Failed to get asset file list.", e);
  }
    
  for(String filename : files) {
    InputStream in = null;
    OutputStream out = null;
    try {
      in = assetManager.open("img/" + filename);
      File outFile = new File(sdCardPath +"/", filename);
      out = new FileOutputStream(outFile);
      copyFile(in, out);
      in.close();
      in = null;
      out.flush();
      out.close();
      out = null;
    } catch(IOException e) {
      Log.e("tag", "Failed to copy asset file: " + filename, e);
    }
  }
}

private void copyFile(InputStream in, OutputStream out) throws IOException {
  byte[] buffer = new byte[1024];
  int read;
  while((read = in.read(buffer)) != -1){
    out.write(buffer, 0, read);
  }
}