我以压缩格式从webview下载文件，但无法在Android

Question

 mWebView.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();
                }
            });

我能够以zip格式下载该文件但无法打开它。任何人都可以帮我找出确切的问题吗？