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Jobs are scheduled to run when a given Trigger occurs. Triggers can be created with nearly any combination of the following directives:
at a certain time of day (to the millisecond)
on certain days of the week
on certain days of the month
on certain days of the year
not on certain days listed within a registered Calendar (such as business holidays)
repeated for a specific number of times
repeated until a specific time/date
repeated indefinitely
repeated with a delay interval
Jobs are named by their creator and can also be organized into named groups. Triggers may also be named and placed into groups, in order to easily organize them within the Scheduler. Jobs can be added to the Scheduler once, but registered with multiple Triggers. Within a J2EE environment, Jobs can perform their work as part of a distributed (XA) transaction.
(Source: quartz-scheduler.org)