Nobody, from what I can tell, is saying "can't". You did ask, though.
If you're willing to be diligent about coding your threads, go for it. I think the point of previous posts was that in many cases, there is no need for such a thing as your asking. There are always exceptions to the rule, though.
For example: the question "is it past midnight" would never be asked if you were to use the operating system, since with something like cron (built in scheduler), the operating already knows if its past midnight. Thus, the question becomes not a question but a command: "its past midnight, go find all of the people who have a status of X and remind them to change their status to Y." The effort, then, is spent on the business logic, not on trying to figure out if its time to spend time on the business logic.
The alternative is to spend resources constantly wondering if a specific time is reached. For one or two events, no problem. Start getting busy, start having 10 or 20 events, and it becomes a problem, not just from a resource standpoint, but from an administration and synchronization standpoint.
John
Riaan Oberholzer wrote:
Perhaps I should give a better explanation of how the application works:
I deliver a .war file. I do have access to an underlying database. The scheduled tasks perform more on a "is time reached" than "has time elapsed" principle... eg, it triggers when "is it past midnight?" instead of "has 24 hours elapsed?".
I cannot see why creating a daemon thread cannot cater for this. You just start the thread in the init method of the InitServlet (or any servlet you create with start-when-app-starts).
What am I missing here? Why can't I use this method? If Tomcat crashes and the app gets restarted, my thread will be restarted as well, so no problem there. The thread should also only be running while the web-app is (LONG story why that is so, so I won't give details... in short, if the web-app is down, it is seen as critical and all else must be halted).
--- John Turner <[EMAIL PROTECTED]> wrote:
cron = scheduler---------------------------------------------------------------------
wget = command line HTTP/HTTPS client
The requirement for delivering everything in a WAR
file is all nice and dandy, but if you think about it, the requirement
automatically breaks the other requirement: scheduling.
If you cannot have a log file, and you cannot access
a database, how will you ever be able to determine elapsed time,
which is the primary requirement for a scheduler? How can you determine
status like when was the last time it was run, etc? How can you reset
your clock if the app is shutdown? How do you know the app has been
shutdown due to an external event?
John
Riaan Oberholzer wrote:
... nice suggestion, but I am delivering an application as a .war file to a 3rd party and they just want the .war (+ context.xml) with everything
in
it.... hence, no other applications checking the
logs
or database. All functionality must come from the
.war
running in Tomcat. It is very important: all functionality must be encapsulated in the .war
file.
(I have no idea what cron +wegt is???)
I guess a daemon thread will be my choice solution
for
now... what the thread does, is check a database
daily
for a certain false condition and send an e-mail
to
all users in question warning them about the
current
status. E.g. if you have to submit your timesheet
by
Friday 17:00, then you'll get a warning on Friday
at
12:00 if it is not done yet.... something like
that.
--- Tim Funk <[EMAIL PROTECTED]> wrote:
Tomcat doesn't provide this but other simple
solutions exist such as exposing a URL and using cron + wget. (Some may also say
kludge too)
As for aggregating statistics - I would recommend
using a log file to record the essential measurements then running your stats
program on the logs. This way - tomcat can crash (or other strange
occurences
may occur) and you lose no data. If the data is already logged, then the
first solution (cron + wget) will work well too.
-Tim
Riaan Oberholzer wrote:
Well, that was part of my question.... if I cannot/don't implement daemon threads to do e.g. automatic daily tasks, what else? E.g, at the end
of
the day send an e-mail to a (real life) manager
with a
summary of the day's transactions.... something
like
that.
Does Tomcat provide some sort of ActionEvent
which
you
can configure to be fired every x milliseconds?
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