Cron Expressions
Cron-Expressions are used to configure instances ofCronTrigger. Cron-Expressions are strings that are actually made up of sevensub-expressions, that describe individual details of the schedule. These sub-expressionare separated with white-space, and represent:
1.Seconds
2.Minutes
3.Hours
4.Day-of-Month
5.Month
6.Day-of-Week
7.Year (optional field)
Anexample of a complete cron-expression is the string “0 0 12 ? * WED”– which means”every Wednesday at 12:00:00 pm”.
Individualsub-expressions can contain ranges and/or lists. For example, the day of weekfield in the previous (which reads “WED”) example could be replacedwith “MON-FRI”,”MON,WED,FRI”, or even”MON-WED,SAT”.
Wild-cards(the ‘‘ character) can beused to say “every” possible value of this field. Therefore the ‘‘ character in the”Month” field of the previous example simply means “everymonth”. A ‘*’ in the Day-Of-Week field would therefore obviously mean”every day of the week”.
Allof the fields have a set of valid values that can be specified. These valuesshould be fairly obvious – such as the numbers 0 to 59 for seconds and minutes,and the values 0 to 23 for hours. Day-of-Month can be any value 1-31, but youneed to be careful about how many days are in a given month! Months can bespecified as values between 0 and 11, or by using the strings JAN, FEB, MAR,APR, MAY, JUN, JUL, AUG, SEP, OCT,NOV and DEC. Days-of-Week can be specified asvalues between 1 and 7 (1 = Sunday) or by using the strings SUN, MON, TUE, WED,THU, FRI and SAT.
The’/’ character can be used to specify increments to values. For example, if youput ‘0/15’ in the Minutes field, it means ‘every 15th minute of the hour,starting at minute zero’. If you used ‘3/20’ in the Minutes field, it wouldmean ‘every 20th minute of the hour, starting at minute three’ – or in otherwords it is the same as specifying ‘3,23,43’ in the Minutes field. Note thesubtlety that “/35″ does *notmean “every 35 minutes” – it mean”every 35th minute of the hour, starting at minute zero” – or inother words the same as specifying ‘0,35’.
The’?’ character is allowed for the day-of-month and day-of-week fields. It isused to specify “no specific value”. This is useful when you need tospecify something in one of the two fields, but not the other. See the examplesbelow (and CronTrigger JavaDoc) for clarification.
The’L’ character is allowed for the day-of-month and day-of-week fields. Thischaracter is short-hand for “last”, but it has different meaning ineach of the two fields. For example, the value “L” in theday-of-month field means “the last day of the month” – day 31 forJanuary, day 28 for February on non-leap years. If used in the day-of-weekfield by itself, it simply means “7” or “SAT”. But if usedin the day-of-week field after another value, it means “the last xxx dayof the month” – for example “6L” or “FRIL” both mean”the last friday of the month”. You can also specify an offset fromthe last day of the month, such as “L-3” which
wouldmean the third-to-last day of the calendar month. When using the ‘L’ option, it is importantnot to specify lists, or ranges of values, as you’ll get confusing/unexpectedresults.
The’W’ is used to specify the weekday (Monday-Friday) nearest the given day. As anexample, if you were to specify “15W” as the value for theday-of-month field, the meaning is: “the nearest weekday to the 15th ofthe month”.
The’#’ is used to specify “the nth” XXX weekday of the month. Forexample, the value of “6#3” or “FRI#3” in the day-of-weekfield means “the third Friday of the month”.
Hereare a few more examples of expressions and their meanings – you can find evenmore in the JavaDoc for org.quartz.CronExpression
Example Cron Expressions
CronTriggerExample 1 – an expression to create a trigger that simply fires every 5 minutes
“0 0/5 * * * ?”
CronTriggerExample 2 – an expression to create a trigger that fires every 5 minutes, at 10seconds after the minute (i.e. 10:00:10 am, 10:05:10 am, etc.).
“10 0/5 * * * ?”
CronTriggerExample 3 – an expression to create a trigger that fires at 10:30, 11:30,12:30, and 13:30, on every Wednesday and Friday.
“0 30 10-13 ? * WED,FRI”
CronTriggerExample 4 – an expression to create a trigger that fires every half hourbetween the hours of 8 am and 10 am on the 5th and 20th of every month. Notethat the trigger will NOT fire at 10:00 am, just at 8:00, 8:30, 9:00 and 9:30
“0 0/30 8-9 5,20 * ?”
Notethat some scheduling requirements are too complicated to express with a singletrigger – such as “every 5minutes between 9:00 am and 10:00 am, and every20 minutes between 1:00 pm and 10:00 pm”. The solution in this scenario isto simply create two triggers, and register both of them to run the same job.
