Cron expression use

Planning tasks , It's a task to carry out the planned work at the appointed time , This is the surface meaning . stay Linux in , We often use cron Server to do this .cron The server can perform specific tasks according to the time agreed in the configuration file .

Introduce

One cron The expression is made up of 6~7 Composed of domains , And a space delimited string .cron It turned out to be unix One of the tools in . It is mainly used for scheduling tasks .cron The core use is cron Expression to handle task scheduling .

Domain explanation

A complete cron The expression has a total of 7 Domains , From left to right means seconds 、 branch 、 Hours 、 Date in month 、 month 、 Date of the week 、 year
The year item is optional , Not necessarily , Therefore, generally, the year is not written for the scheduled task , This is the 6 position .

cron Relevant symbols and uses

• ﹡： Allow this field to use all values
• ?： Only allowed in 4 Domains （ Date in month ） And the 6 Domains （ Date of the week ）, Indicates that the value of this field is not considered , Because the data in the two domains may conflict
• -： This symbol identifies the range
• ,： This symbol represents multiple values in a field in parallel
• /： This symbol sets the step size
• L： Said the last
• W： It means week 1 By the end of the week 5, This symbol can only appear in 4 Fields and can only be combined with other values
• #： This symbol can only appear in 6 In a domain （ Date of the week ）, Indicates the day of the month

stay Linux The use of

stay linux Use in crontab Command to operate cron, The code is as follows ：

man crontab # see crontab Help document for 

View the set scheduled tasks

crontab -l

have access to man Help documents to learn crontab command .

stay spring Use in

In normal development , Need to write scheduled tasks , We can use spring Of @Scheduled annotation , Set up a cron Set the value of .

@Scheduled(cron="10 * * * * ?")
public void scheduledTask(){
    
	/****do somethings***/
}