如何在PDF文档之前显示加载屏幕

Question

In our application we have links to dynamically generated PDF documents. The links look something like this host/22-5/file_3136.pdf so to the browser it seems like a static pdf document. When link is clicked it opens a new window. That window receives PDF document only (no HTML) with headers like:

Content-Disposition: inline; filename=file_3136.pdf
Content-Type: application/pdf

We want users to be able to see the PDF in the browser if PDF plug-in is installed and to be able save the document with correct filename.

Now we want to add a loading screen that would be shown while the PDF is being generated. Whats the best way to do that, while retaining the current functionality.

One option would be to show the loading screen and then to redirect to PDF when generation is complete. This would require me to retain the PDF on the server for some time. Currently they are being deleted as soon as the response is sent.

Another option is to send some HTML and javascript (to show the loading page) with <embed> , <iframe> or <object> tag that points to the pdf on the server.

What the best approach? What works with most browsers?

Answer 1

On download sites, I often see an additional (small) window pop up. I believe that window acts as a "choreographer" to control what displays on the main page while also firing off a redirect to the download file.

Answer 2

HTML redirects. You create a page that redirects "to itself" every few seconds. When the PDF is done, you generate a redirect to that instead.

Answer 3

To actually preload the PDF file so that the impression of instant loading is given. in the page prior to the pdf linked page add a preload script:

<img id="pdfLoader" src="preloader.jpg"/>

You can get a preloader image from ajaxload.info

<script language="javascript" type="text/javascript">
//<![CDATA[
<!-- 
var pdfLoader = document.getElementById("pdfLoader");
pdfLoader.src = "http://mysite.com/mypdf.pdf";
//-->
//]]>
</script>

The code above placed between and in the page containing the link to the .pdf file (or html file with the .pdf in it) instructs the browser to download the pdf file to the browser cache, but just leave it there. (filetype is irelevant image() is convenient, use the same script for any filetype as it is not ever going to be rendered) the download happens after the page is fully rendered so does not delay the current page. on clicking the link to the .pdf file (or html page) the browser finds the .pdf in the browser cache and does not download it, but displays from the cache, at apparently blinding download speeds.

In browsers with javascript disabled, the function degrades gracefully

Answer 4

If you linearize the PDf you can also display the first page very quickly. I wrote 2 articles introducing linearized PDF at http://www.jpedal.org/PDFblog/2010/11/do-i-have-to-download-the-whole-pdf-if-i-view-it-across-the-internet/ and http://www.jpedal.org/PDFblog/2010/02/linearized-pdf-files/