Facilitates scheduled task execution at runtime using a flexible, cron-like syntax. Supports configuration via strings or DSL builders, local and timezone-aware scheduling, and conversion to reactive flows.
Library was created to give oppotunity to launch some things from time to time according to some schedule in runtime of applications.
There are several ways to configure and use this library:
Anyway, to start some action from time to time you will need to use one of extensions/functions:
val kronScheduler = /* creating of KronScheduler instance */;
kronScheduler.doWhile {
// some action
true // true - repeat on next time
}
If you want to include krontab in your project, just add next line to your
dependencies part:
implementation "dev.inmo:krontab:$krontab_version"
Next version is the latest currently for the library:
For old version of Gradle, instead of implementation word developers must use compile.
Developers can use more simple way to configure repeat times is string. String configuring
like a crontab, but with a little bit different meanings:
/--------------- Seconds
| /------------- Minutes
| | /----------- Hours
| | | /--------- Days of months
| | | | /------- Months
| | | | | /----- (optional) Year
| | | | | | /--- (optional) Timezone offset
| | | | | | | / (optional) Week days
* * * * * * 0o *w
It is different with original crontab syntax for the reason, that expected that in practice developers
will use seconds and minutes with more probability than months (for example) or even years. In fact, developers will use
something like:
doWhile("/5 * * * *") {
println("Called")
true // true - repeat on next time
}
An other version:
doInfinity("/5 * * * *") {
println("Called")
}
Both of examples will print Called message every five seconds.
Also, this library currently supports DSL for creating the same goals:
val kronScheduler = buildSchedule {
seconds {
from (0) every 5
}
}
kronScheduler.doWhile {
println("Called")
true // true - repeat on next time
}
Or
val kronScheduler = buildSchedule {
seconds {
0 every 5
}
}
kronScheduler.doWhile {
println("Called")
true // true - repeat on next time
}
Or
val kronScheduler = buildSchedule {
seconds {
0 every 5
}
}
kronScheduler.doInfinity {
println("Called")
}
All of these examples will do the same things: print Called message every five seconds.
With regular doOnce/doWhile/doInfinity there are two types of their variations: local and timezoned. Local
variations (doOnceLocal/doWhileLocal/doInfinityLocal) will pass as an argument into the block:
doInfinityLocal("/5 * * * *") {
println(it) // will print current date time
}
Timezoned variations (doOnceTz/doWhileTz/doInfinityTz) will do the same thing but pass as an argument DateTimeTz:
doInfinityTz("/5 * * * * 0o") {
println(it) // will print current date time in UTC
}
It is useful in cases when you need to get the time of calling and avoid extra calls to system time.
*Here there is an important notice, that Work infinity is not exactly infinity. Actually, that means that do while coroutine is alive and in fact executing will be stopped when coroutine became cancelled.
Any KronSchedulercan e converted to a Flow<DateTime using extension asFlow:
val kronScheduler = buildSchedule {
seconds {
0 every 1
}
}
val flow = kronScheduler.asFlow()
So, in this case any operations related to flow are available and it is expected that they will work correctly. For
example, it is possible to use this flow with takeWhile:
flow.takeWhile {
condition()
}.collect {
action()
}
Offsets in this library works via passing parameter ending with o in any place after month config. Currently
there is only one format supported for offsets: minutes of offsets. To use time zones you will need to call next
method with DateTimeTz argument or nextTimeZoned method with any instance, but in case if this
scheduler is not instance of it will work like you passed just .
Besides, in case you wish to use time zones explicitly, you will need to get KronSchedulerTz. It is possible by:
Unlike original CRON, here week days:
AND: cron date time will search first day which will pass requirement according all parameters including
week days0-3w, 0,1,2,3w, etc.monthDateTime| No args | Local DateTime | Local DateTimeTz with offset of KronScheduler |
|---|
| Call only near time | doOnce | doOnceLocal | doOnceTz |
| Call while condition is true | doWhile | doWhileLocal | doWhileTz |
| Work infinity* | doInfinity | doInfinityLocal | doInfinityTz |
KronSchedulerKronSchedulerTzDateTimecreateSimpleScheduler/buildSchedule/KrontabTemplate#toSchedule/KrontabTemplate#toKronScheduler methods
with passing defaultOffset parameterSchedulerBuilder#build/createSimpleScheduler/buildSchedule/KrontabTemplate#toSchedule/KrontabTemplate#toKronScheduler
methods with casting to KronSchedulerTz in case you are pretty sure that it is timezoned KronSchedulerKronSchedulerTzSurfaced from shared tags and platforms — no rankings paid for.