Scheduled Apex - CronExpression Question

Question

I am currently having difficulty in understanding the CronExpression parameter for System.schedule() method.

As per doc it says the syntax is

"Minutes, Hours, Day of month, Month, Day of week, optional Year"

http://www.salesforce.com/developer/docs/api/Content/sforce_api_objects_crontrigger.htm

I scheduled a job from UI and when I queried on the CronTrigger field for CronExpression I got

"0 0 9 ? * 1,2,3,4,5,6,7"

The job above is scheduled to run at 9:00 AM on all days. I could infer "all days" is reflected by "1,2,3,4,5,6,7" but then it does not match with the doc's syntax reference.

I am lil confused.

Also can someone let me know what should be the CronExpression for hourly job (runs at every hour..say 9:00 AM, 10:00 AM, 11:00 AM etc).

Answer 1

If you have a look at the System.Schedule method documentation here it provides a detailed breakdown of how the CRON expression can be configured. To go through yours piece by piece (numbers in brackets on second line are a reference for us to use):

 0   0   9   ?   *  1,2,3,4,5,6,7
{1} {2} {3} {4} {5} {6}

{1} Number of seconds past the minute, so 0 here i.e. start of the minute.

{2} Number of minutes past the hour, 0 again so start of the hour.

{3} Hour of the day, 9 so 9 am. Uses 24 hour notation so 21 = 9pm

{4} Day of the month, ? means no specific value, only available for day of the month and day of the week. Should use ? on one when detailing the other

{5} Month (if we only want to run on 1st Jan say, this would be 1). * indicates all values, i.e. every month

{6} Day of the week. 1,2,3,4,5,6,7 here specifies days 1,2,3,4,5,6,7 in the week. We could also write this string as MON-FRI or preferably as * to indicate all values.

So your job reads to run at "0 seconds past 0 minutes of the 9th hour on no specified day of the month for every month of the year for every day of the week"

Answer 2

CronExpression for hourly job: '0 0 * * * ?'