Cron Expression

A cron expression is a string that represents the schedule for the execution of a job. A cron expression consists of six or seven fields (time units).

1. Cron Expression Structure

A Cron Expression consists of seven fields separated by spaces:

<second> <minute> <hour> <day-of-month> <month> <day-of-week> <year>
Field Required? Allowed Values Special Characters Description
Seconds Required 0-59 , - * / Specifies the second.
Minutes Required 0-59 , - * / Specifies the minute.
Hours Required 0-23 , - * / Specifies the hour.
Day-of-Month Required 1-31 , - * ? / L W Specifies the day of the month.
Month Required 1-12 or JAN-DEC , - * / Specifies the month.
Day-of-Week Required 1-7 or SUN-SAT , - * ? / L # Specifies the day of the week.
Year Optional 1970-2099 , - * / Specifies the year. Automatically generate, the tool does not display this value.

2. Special Characters and Their Meanings

Cron Expressions support several special characters to define complex scheduling rules:

* (Asterisk)

  • Matches all possible values for the field.
  • Example: * * * * * ? (Every second of every minute of every hour)

, (Comma)

  • Specifies a list of values.
  • Example: 0 0 9,15 * * ? (At 9:00 AM and 3:00 PM every day)

- (Dash)

  • Specifies a range of values.
  • Example: 0 0 10-12 * * ? (Every hour between 10:00 AM and 12:00 PM)

/ (Slash)

  • Specifies increments.
  • Example: 0 0/15 * * * ? (Every 15 minutes)

? (Question Mark)

  • Used in either the Day-of-Month or Day-of-Week fields to specify "no specific value."
  • Example: 0 0 10 ? * MON-FRI (At 10:00 AM Monday through Friday)

L (Last)

  • Used in Day-of-Month or Day-of-Week fields to specify the last day.
  • Example: 0 0 0 L * ? (Midnight on the last day of every month)
  • Example: 0 0 0 ? * 5L (Midnight on the last Friday of every month)

W (Weekday)

  • Specifies the nearest weekday (Monday to Friday) to a given day.
  • Example: 0 0 0 15W * ? (Midnight on the nearest weekday to the 15th of the month)

# (Nth Day of Week)

  • Specifies the nth occurrence of a day in a month.
  • Example: 0 0 0 ? * 2#1 (Midnight on the first Monday of every month)

.3 Practical Examples

Here are some practical examples Cron Expressions:

  1. Every second:

    * * * * * ?

  2. Every minute:

    0 * * * * ?

  3. Every day at midnight:

    0 0 0 * * ?

  4. Every 5 minutes between 9:00 AM and 5:00 PM:

    0 0/5 9-17 * * ?

  5. At 10:30 AM on the 1st and 15th of every month:

    0 30 10 1,15 * ?

  6. At 8:00 AM on the last Friday of every month:

    0 0 8 ? * 6L

  7. At noon on weekdays:

    0 0 12 ? * MON-FRI

  8. Every 30 seconds starting at 5 seconds past the minute:

    5/30 * * * * ?

4. Common Mistakes and Best Practices

1. Day-of-Month and Day-of-Week Conflict

  • Avoid specifying both fields simultaneously.
  • Use ? in one of the fields to avoid ambiguity.

2. February Dates

  • Ensure the Day-of-Month value is valid for February (e.g., 29 only works in leap years).

3. Year Field

  • The Year field is optional. If omitted, the Cron Expression will run for all years.

4. Overflowing ranges is supported

  • that is, having a larger number on the left hand side than the right. You might do 22-2 to catch 10 o'clock at night until 2 o'clock in the morning, or you might have NOV-FEB.
  • It is very important to note that overuse of overflowing ranges creates ranges that don't make sense and no effort has been made to determine which interpretation CronExpression chooses.

results matching ""

    No results matching ""