Android webview: download files like browsers do

Finally i decided to look for the DownloadHandler from the Android Stock Browser code. The only noticeable lack in my code was cookie (!!!).

Here's my final working version (DownloadManager method):

    wv.setDownloadListener(new DownloadListener() {
        @Override
        public void onDownloadStart(String url, String userAgent, String contentDisposition, String mimeType, long contentLength) {
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));

            request.setMimeType(mimeType);
            //------------------------COOKIE!!------------------------
            String cookies = CookieManager.getInstance().getCookie(url);
            request.addRequestHeader("cookie", cookies);
            //------------------------COOKIE!!------------------------
            request.addRequestHeader("User-Agent", userAgent);
            request.setDescription("Downloading file...");
            request.setTitle(URLUtil.guessFileName(url, contentDisposition, mimeType));
            request.allowScanningByMediaScanner();
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, URLUtil.guessFileName(url, contentDisposition, mimeType));
            DownloadManager dm = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
            dm.enqueue(request);
            Toast.makeText(getApplicationContext(), "Downloading File", Toast.LENGTH_LONG).show();
        }
    });

With this option I managed to download complete files, the download worked with other options but the documents appeared empty, especially when a session is being used.

Add below lines to AndroidManifest.xml

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

Add DownloadListener to your WebView

Try this code

wv.setDownloadListener(new DownloadListener() {
    @Override
    public void onDownloadStart(final String url, final String userAgent, String contentDisposition, String mimetype, long contentLength) {
        //Checking runtime permission for devices above Marshmallow.
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            if (checkSelfPermission(android.Manifest.permission.WRITE_EXTERNAL_STORAGE)
                    == PackageManager.PERMISSION_GRANTED) {
                Log.v(TAG, "Permission is granted");
                downloadDialog(url, userAgent, contentDisposition, mimetype);

            } else {

                Log.v(TAG, "Permission is revoked");
                //requesting permissions.
                ActivityCompat.requestPermissions(PortalActivity.this, new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE}, 1);

            }
        } else {
            //Code for devices below API 23 or Marshmallow
            Log.v(TAG, "Permission is granted");
            downloadDialog(url, userAgent, contentDisposition, mimetype);

        }
    }
});

//downloadDialog Method

public void downloadDialog(final String url, final String userAgent, String contentDisposition, String mimetype) {
    //getting filename from url.
    final String filename = URLUtil.guessFileName(url, contentDisposition, mimetype);
    //alertdialog
    AlertDialog.Builder builder = new AlertDialog.Builder(this);

    //title of alertdialog
    builder.setTitle(R.string.download_title);
    //message of alertdialog
    builder.setMessage(getString(R.string.download_file) + ' ' + filename);
    //if Yes button clicks.

    builder.setPositiveButton(getString(R.string.yes), new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            //DownloadManager.Request created with url.
            DownloadManager.Request request = new DownloadManager.Request(Uri.parse(url));
            //cookie
            String cookie = CookieManager.getInstance().getCookie(url);
            //Add cookie and User-Agent to request
            request.addRequestHeader("Cookie", cookie);
            request.addRequestHeader("User-Agent", userAgent);
            //file scanned by MediaScannar
            request.allowScanningByMediaScanner();
            //Download is visible and its progress, after completion too.
            request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE_NOTIFY_COMPLETED);
            //DownloadManager created
            DownloadManager downloadManager = (DownloadManager) getSystemService(DOWNLOAD_SERVICE);
            //Saving files in Download folder
            request.setDestinationInExternalPublicDir(Environment.DIRECTORY_DOWNLOADS, filename);
            //download enqued
            downloadManager.enqueue(request);
        }
    });
    builder.setNegativeButton("No", new DialogInterface.OnClickListener() {
        @Override
        public void onClick(DialogInterface dialog, int which) {
            //cancel the dialog if Cancel clicks
            dialog.cancel();
            mWebView.goBack();
        }

    });
    //alertdialog shows.
    builder.show();

}