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Message-ID: <44D094B7.5080700@cornell.edu>
Date: Wed, 02 Aug 2006 08:04:07 -0400
From: David Smith <dns4@cornell.edu>
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To: Tomcat Users List <users@tomcat.apache.org>
Subject: Re: [OT?] Servlet, redirect and progress-monitoring?
References: <44D08CD7.3030301@zimmer428.net>
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I suspect what you really have to do is set the PDF generation off into 
a background thread, storing a reference to the thread in the session.  
Then return with a refresh every 10 - 15 seconds until the thread 
finishes.  Clean up after the thread so you don't end up with memory 
leaks and possibly implement a listener to clean-up any abandon threads 
when the session is destroyed.

--David

Kristian Rink wrote:

>Hi all,
>
>being aware that this is not a question strictly tomcat-relevant,
>lacking a really good mailing-list for discussions closer to the J2EE
>background itself, I hope for some input by all the gurus out there.
>
>I'm into a situation like this: A servlet gathers statistical
>information across the data in our DMS, is supposed to make a PDF out of
>them and send them back to the client who requested them (PDF is demanded).
>
>Problem, however, is that sometimes these computations take quite some
>time, leaving me with two situations: (a) The browser itself considers
>the connection to be "timed out" as the servlet is stuck in doGet() for
>a bunch of minutes. (b) The user itself considers the connection to be
>"dead" and closes the browser window. Both situations are uncomfortable.
>
>
>By now, my initial idea was something like that, utilizing two servlets:
>
>- Servlet 1 processes the request and immediately redirects the client
>to another servlet while finishing the calculations and creating the PDF
>file.
>
>- Servlet 2 refreshes, say, each 2 seconds, checking whether the file in
>question finally has been created and put in place to, then, send this
>back to the browser.
>
>
>This, however, doesn't work out as Servlet 1, even though sending the
>Redirect, doesn't redirect until leaving doGet(). So, that's not the
>solution...
>
>
>My question, now: Is there any "usual" / "best-practise" way of doing
>something like that, of presenting people with a "please-stand-by" page
>while there is activity goin' on in background? Is there a way of
>solving something like this without being in need of JavaScript/AJAX/DWR
>or something the like?
>
>Any hints, even just pointers to good documentation on that issue, are
>very much appreciated.
>
>Thanks and bye,
>Kristian
>
>
>  
>


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