i used the servlet api as a wrapper for my "cron-like"
JobManager code so that it could be fired up when the
server started up. short of that, it is not <presently>
tickled in any manner by http although having that hook
is not necessarily a bad thing.
hope this helps,
- james
> Brian Zimbelman wrote:
>
> Guys,
>
> Why is it that people seem to want to make everything a servlet? What
> about this cron class is servlet like? Is it getting invoked by a http
> request? When I wrote our cron-like utility (very basic replacement
> that handles what we need, doesn't have all the bells and whistles of
> cron, runs on all platforms, controlled via our database not crontab
> files) I wrote it as a Java application.
>
> Just curious as to what I'm missing, as I tend to put everything that
> is not about handling requests from the user and building HTML
> responses in something other than the servlets (clean separation of
> the model and the view in my mind).
>
> Thanks,
> Brian
>
> -----Original Message-----
> From: Tim Panton [mailto:[EMAIL PROTECTED]]
> Sent: Saturday, August 21, 1999 4:52 AM
> To: [EMAIL PROTECTED]
> Subject: Re: Using servlets for periodic background processes
>
> > Nic Ferrier wrote:
> > >
> > > Personally I think it's a bad idea.
> > >
> >
> > Hi,
> >
> > The idea sounds good to me. :) This servlet-cron service would
> simply
> > run in its own thread, and wakes up periodically. This could be
> > configured depending on the site's design. Maybe every 30 seconds
> > would be a good start. It would check if there's any tasks at that
> > point in time to be done, and when through go back to sleep
>
> I don't think a generic cron replacement servlet is a good idea,
> Cron has lots of nice properties that are hard to do in the servlet
> environment like :
> Persistence across reboots/crashes
> correct actions over DST changes (allegedly)
> reliable one-shot actions
> run as less (or more) privileged user
>
> If however you have a bit of servlet (or webapp) related periodic
> activity,
> then it is fine to code up a thread to be spun off from a servlet,
> but be very aware of the servlet lifecycle as it is implemented in
> your
> web server/engine.
>
> Here are a couple of things that might trip you up:
> 1) In some engines servlets are not loaded until the first
> use,
> so your cron-servlet may never be loaded unless you take special
> steps.
> 2) Some engines will destroy a servlet that's been idle for a
> long
> time, and then subsequently start a new instance. Your background
> thread
> however may still have a reference to the old servlet, and update the
> state
> of the 'destroyed' one.
> 3) Some engines have multiple VM's running, be sure that the
> cron
> servlet is in the one you want, i.e. the JVM serving https: servlets
> may
> not
> be the same as the one serving http: servlets.
>
> None of these issue are insurmountable, but they sure can slow you
> down,
> as I've discovered.
>
> T.
>
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