如何在webView andorid中下载pdf文件

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

webView.setWebChromeClient(new WebChromeClient() {
    @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);
        String cookies = CookieManager.getInstance().getCookie(url);
        request.addRequestHeader("cookie", cookies);
        request.addRequestHeader("User-Agent", userAgent);
        request.setDescription("Downloading PDF 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 downloadManager = (DownloadManager) getSystemService(Context.DOWNLOAD_SERVICE);
        downloadManager.enqueue(request);
    }
});

webView.getSettings().setJavaScriptEnabled(true);
webView.getSettings().setAllowFileAccess(true);