Копировать все данные из asset

basePath - из которой, outPath - в которую.

private void copyAssets(String outPath, String basePath)
{
    InputStream inputStream;
    AssetManager assetManager = getAssets();

    try {
        String[] assets = assetManager.list(basePath);
        for (String s: assets)
        {
            String[] tmp = assetManager.list(basePath+"/"+s);
            if (tmp.length > 0)
            {
                File dir = new File(outPath + "/" + s);
                dir.mkdir();
                copyAssets(outPath + "/" + s, basePath + "/" + s);
                continue;
            }
            byte[] inputBuffer = new byte[1000];
            int count;

            FileOutputStream f = new FileOutputStream(outPath + "/" + s);
            inputStream = assetManager.open(basePath + "/" + s);
            while ((count = inputStream.read(inputBuffer)) > 0)
                f.write(inputBuffer, 0, count);

            f.close();

        }
    }catch (Exception e) {
        e.printStackTrace();
    }       
}