geronimo-dev mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Aaron Mulder" <ammul...@alumni.princeton.edu>
Subject Re: GBeans representing separately persistent data
Date Mon, 12 Jun 2006 00:34:17 GMT
I looked at the developerworks article.  The GBean there is extremely
simple.  It starts a Quartz scheduler, but has no code or methods to
configure it or do anything with it.  I think it was more a
demonstration of how to write a GBean than anything else.

As for why I wanted to represent jobs as GBeans, it's so you can
deploy and manage them.  That is, you can deploy a job, start it, stop
it, or undeploy it, as well as managing its schedule, executing it
immediately, querying the last time it ran and the next time it'll
run, etc.  Since it's a unit that can be deployed and managed, it
seemed logical to represent it as a GBean.

I guess the alternative you're suggesting is to expose the scheduler
as a GBean and if you want to do anything with jobs you have to
interact with the scheduler GBean and call methods on it.  That would
work, but I don't think it's as nice in practice.  For one thing, I'm
not sure how you'd get the job classes to the scheduler -- it seems
like you might need to alter the scheduler module to add more
dependencies every time you added new jobs -- at least if you were
using a database for job persistence.  Also, if you want to add a job,
you need to write some kind of code to access the scheduler and add
the job, which seems a little onerous.

With the job-as-GBean approach, in contrast, you can pack your job
classes in a JAR with a plan that defines the schedule, and deploy
that using the normal Geronimo deployment tools.  Then in addition to
convenient deployment, they each get their own class loader, and can
declare dependencies on other application modules (e.g. to get the
classes necessary to call a session bean).

Thanks,
    Aaron

On 6/11/06, David Jencks <david_jencks@yahoo.com> wrote:
>
> On Jun 11, 2006, at 4:20 PM, Aaron Mulder wrote:
>
> > So I've been playing around with a Quartz integration plugin.  My
> > first stab only supported an in-memory schedule, but Quartz also
> > supports storing to a database.  Here's my issue with that.
> >
> > Right now I have a GBean representing a scheduled job.  When you start
> > it, the job is scheduled.  When you stop it, the job is deleted.
> > Therefore when you start the server, the scheduler is started and the
> > deployed jobs are started, and I guess they're effectively persistent
> > using config.xml as storage instead of using a DB.
>
> I've never used quartz but the idea of a job as a gbean seems odd to
> me.  I would expect there would be one quartz gbean and everything
> you scheduled would be saved in a database.  Can you provide a lot
> more detail about what the job gbean is like?  So far I don't get it,
> it seems like extreme impedance mismatch.
>
>
> >
> > So let's say we let you store the job info to a database.  What
> > happens to the job GBeans?  You can take down the server, delete all
> > your jobs from config.xml, add some new jobs to the database, and
> > start the server again.  So the GBeans can get totally out of sync
> > with the data they represent.
> >
> > I guess what would be most appropriate for this case would be some
> > kind of "transient GBean" that does not save to config.xml.  So when
> > the scheduler starts it could create GBeans representing all the jobs,
> > which you could use to manage it, but changes to the GBeans would only
> > affect the Quartz database (not config.xml) and when you shut down
> > they'd all go away.  Until next time you start up, and the scheduler
> > would recreate all the job GBeans again.  What do you think?
>
> I don't get why these are "gbeans".   I must be missing something
> important here.
> >
> > The alternative is to keep using GBeans as persistence, and just add
> > GBeans to represent calendars and triggers, which are the other two
> > fundamental types in Quartz.  That certainly seems like the more
> > expedient path for now.
>
> I also don't understand why these other types would be gbeans
> either.  I'd really appreciate more detail on this.  This could well
> be the best model, but I don't see why yet :-)
>
> BTW I thought jeff already did a quartz integration, in a
> developerworks article, have you looked at what he did?
>
> thanks
> david jencks
>
> >
> > Thanks,
> >     Aaron
>
>

Mime
View raw message