CronTrigger Tutorial——石英调度！

CronTrigger Tutorial

Introduction

cron is a UNIX tool that has been around for a long time, soits scheduling capabilities are powerful and proven. TheCronTrigger class is based on the scheduling capabilities of cron.

CronTrigger uses "cron expressions", which are able tocreate firing schedules such as: "At 8:00am every Monday throughFriday" or "At 1:30am every last Friday of the month".

Cron expressions are powerful, but can be prettyconfusing. This tutorial aims to take some of the mystery out of creating acron expression, giving users a resource which they can visit before having toask in a forum or mailing list.

Format

A cron expression is a string comprised of 6 or 7 fieldsseparated by white space. Fields can contain any of the allowed values, alongwith various combinations of the allowed special characters for that field. Thefields are as follows:

Field Name

Mandatory

Allowed Values

Allowed Special Characters

Seconds

YES

0-59

, - * /

Minutes

YES

0-59

, - * /

Hours

YES

0-23

, - * /

Day of month

YES

1-31

, - * ? / L W

Month

YES

1-12 or JAN-DEC

, - * /

Day of week

YES

1-7 or SUN-SAT

, - * ? / L #

Year

NO

empty, 1970-2099

, - * /

So cronexpressions can be as simple as this: * * * * ? *

or morecomplex, like this: 0/5 14,18,3-39,52 * ? JAN,MAR,SEP MON-FRI 2002-2010

Special characters

·        * ("all values") - usedto select all values within a field. For example, "" in the minute field means *"everyminute".

·        ? ("no specific value") -useful when you need to specify something in one of the two fields in which thecharacter is allowed, but not the other. For example, if I want my trigger tofire on a particular day of the month (say, the 10th), but don't care what dayof the week that happens to be, I would put "10" in the day-of-monthfield, and "?" in the day-of-week field. See the examples below forclarification.

·        - - used to specify ranges. Forexample, "10-12" in the hour field means "the hours 10, 11 and 12".

·        , - used to specify additionalvalues. For example, "MON,WED,FRI" in the day-of-week field means "the days Monday, Wednesday, andFriday".

·        / - used to specify increments. Forexample, "0/15" in the seconds field means "the seconds 0, 15, 30, and 45". And"5/15" in the seconds field means "the seconds 5, 20, 35, and 50". You canalso specify '/' after the ''character - in this case '' is equivalent to having '0'before the '/'. '1/3' in the day-of-month field means "fire every 3 days starting on the firstday of the month".

·        L ("last") - hasdifferent meaning in each of the two fields in which it is allowed. Forexample, the value "L" in the day-of-month field means "the last day of the month" - day 31for January, 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 day of the month" - forexample "6L" means "thelast friday of the month". When using the 'L' option, itis important not to specify lists, or ranges of values, as you'll get confusingresults.

·        W ("weekday") - usedto specify the weekday (Monday-Friday) nearest the given day. As an example, ifyou were to specify "15W" as the value for the day-of-month field,the meaning is: "the nearestweekday to the 15th of the month". So ifthe 15th is a Saturday, the trigger will fire on Friday the 14th. If the 15this a Sunday, the trigger will fire on Monday the 16th. If the 15th is aTuesday, then it will fire on Tuesday the 15th. However if you specify"1W" as the value for day-of-month, and the 1st is a Saturday, thetrigger will fire on Monday the 3rd, as it will not 'jump' over the boundary ofa month's days. The 'W' character can only be specified when the day-of-monthis a single day, not a range or list of days.

The 'L'and 'W' characters can also be combined in the day-of-month field to yield'LW', which translates to *"last weekday of the month"*.

·        # - used to specify "thenth" XXX day of the month. For example, the value of "6#3" inthe day-of-week field means"thethird Friday of the month" (day 6 =Friday and "#3" = the 3rd one in the month). Other examples:"2#1" = the first Monday of the month and "4#5" = the fifthWednesday of the month. Note that if you specify "#5" and there isnot 5 of the given day-of-week in the month, then no firing will occur thatmonth.

The legalcharacters and the names of months and days of the week are not case sensitive. MON is the same as mon.

Examples

Here are some full examples:

Expression

Meaning

0 0 12 * * ?

Fire at 12pm (noon) every day

0 15 10 ? * *

Fire at 10:15am every day

0 15 10 * * ?

Fire at 10:15am every day

0 15 10 * * ? *

Fire at 10:15am every day

0 15 10 * * ? 2005

Fire at 10:15am every day during the year 2005

0 * 14 * * ?

Fire every minute starting at 2pm and ending at 2:59pm, every day

0 0/5 14 * * ?

Fire every 5 minutes starting at 2pm and ending at 2:55pm, every day

0 0/5 14,18 * * ?

Fire every 5 minutes starting at 2pm and ending at 2:55pm, AND fire every 5 minutes starting at 6pm and ending at 6:55pm, every day

0 0-5 14 * * ?

Fire every minute starting at 2pm and ending at 2:05pm, every day

0 10,44 14 ? 3 WED

Fire at 2:10pm and at 2:44pm every Wednesday in the month of March.

0 15 10 ? * MON-FRI

Fire at 10:15am every Monday, Tuesday, Wednesday, Thursday and Friday

0 15 10 15 * ?

Fire at 10:15am on the 15th day of every month

0 15 10 L * ?

Fire at 10:15am on the last day of every month

0 15 10 ? * 6L

Fire at 10:15am on the last Friday of every month

0 15 10 ? * 6L

Fire at 10:15am on the last Friday of every month

0 15 10 ? * 6L 2002-2005

Fire at 10:15am on every last friday of every month during the years 2002, 2003, 2004 and 2005

0 15 10 ? * 6#3

Fire at 10:15am on the third Friday of every month

0 0 12 1/5 * ?

Fire at 12pm (noon) every 5 days every month, starting on the first day of the month.

0 11 11 11 11 ?

Fire every November 11th at 11:11am.

Payattention to the effects of '?' and '*' in the day-of-week and day-of-monthfields!

Notes

·        Support for specifying both aday-of-week and a day-of-month value is not complete (you must currently usethe '?' character in one of these fields).

·        Be careful when setting firetimes between mid-night and 1:00 AM - "daylight savings" can cause askip or a repeat depending on whether the time moves back or jumps forward.