Job scheduling with Quartz

Quartz is an open source job scheduling framework that provides simple but powerful mechanisms for job scheduling in Java applications. Quartz allows developers to schedule jobs by time interval or by time of day. The two fundamental units of Quartz's scheduling package are jobs and triggers. A job is an executable task that can be scheduled, while a trigger provides a schedule for a job.
Also, any singular job can have many triggers associated with it.

A CronTrigger allows for more specific scheduling than a SimpleTrigger and is still not very complex. Based on cron expressions, CronTriggers allow for calendar-like repeat intervals rather than uniform repeat intervals -- a major improvement over SimpleTriggers.
A "Cron-Expression" is a string comprised of 6 or 7 fields separated by white space. There are 6 mandatory and 1 optional fields.

Field Name
Seconds
Minutes
Hours
Day-of-month
Month
Day-of-Week
Year (Optional)

Expression Meaning
"0 0 12 * * ?" Fire at 12pm (noon) every day

useful links:
http://www-128.ibm.com/developerworks/java/library/j-quartz/

http://quartz.sourceforge.net/javadoc/org/quartz/CronTrigger.html