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Chapter 142. Scheduler
Scheduler component
Available as of Camel 2.15
The scheduler: component is used to generate message exchanges when a scheduler fires. This component is similar to the Timer component, but it offers more functionality in terms of scheduling. Also this component uses JDK
ScheduledExecutorService. Where as the timer uses a JDK Timer.
You can only consume events from this endpoint.
URI format
scheduler:name[?options]
Where
name is the name of the scheduler, which is created and shared across endpoints. So if you use the same name for all your timer endpoints, only one scheduler thread pool and thread will be used - but you can configure the thread pool to allow more concurrent threads.
You can append query options to the URI in the following format,
?option=value&option=value&...
Note: The IN body of the generated exchange is
null. So exchange.getIn().getBody() returns null.
Options
|
Name
|
Default Value
|
Description
|
|---|---|---|
initialDelay
|
1000
|
Milliseconds before the first poll starts |
delay
|
500
|
Milliseconds before the next poll
|
timeUnit
|
MILLISECONDS
|
time unit for initialDelay and delay options.
|
useFixedDelay
|
true
|
Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details. |
pollStrategy
|
A pluggable org.apache.camel.PollingConsumerPollingStrategy allowing you to provide your custom implementation to control error handling usually occurred during the poll operation before an Exchange have been created and being routed in Camel. In other words the error occurred while the polling was gathering information, for instance access to a file network failed so Camel cannot access it to scan for files. The default implementation will log the caused exception at WARN level and ignore it.
|
|
runLoggingLevel
|
TRACE
|
The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that. |
sendEmptyMessageWhenIdle
|
false
|
If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead. |
greedy
|
false
|
If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the previous run polled 1 or more messages. |
scheduler
|
Allow to plugin a custom org.apache.camel.spi.ScheduledPollConsumerScheduler to use as the scheduler for firing when the polling consumer runs. The default implementation uses theScheduledExecutorService and there is a Quartz2, and Spring based which supports CRON expressions. Notice: If using a custom scheduler then the options for initialDelay, useFixedDelay, timeUnit, andscheduledExecutorService may not be in use. Use the text quartz2 to refer to use the Quartz2 scheduler; and use the text spring to use the Spring based; and use the text #myScheduler to refer to a custom scheduler by its id in the Registry. See Quartz2 page for an example.
|
|
scheduler.xxx
|
To configure additional properties when using a custom scheduler or any of the Quartz2, Spring based scheduler. For example, to specify a cron value for the Spring based scheduler, use scheduler.cron.
|
|
backoffMultiplier
|
0
|
To let the scheduled polling consumer backoff if there has been a number of subsequent idles/errors in a row. The multiplier is then the number of polls that will be skipped before the next actual attempt is happening again. When this option is in use then backoffIdleThreshold and/or backoffErrorThreshold must also be configured.
|
backoffIdleThreshold
|
0
|
The number of subsequent idle polls that should happen before the backoffMultipler should kick-in
|
backoffErrorThreshold
|
0
|
The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in.
|
More information
This component is a scheduler Polling Consumer where you can find more information about the options above, and examples at the Polling Consumer page.
Exchange Properties
When the timer is fired, it adds the following information as properties to the
Exchange:
|
Name
|
Type
|
Description
|
|---|---|---|
Exchange.TIMER_NAME
|
String
|
The value of the
name option.
|
Exchange.TIMER_FIRED_TIME
|
Date
|
The time when the consumer fired.
|
Sample
To set up a route that generates an event every 60 seconds:
from("scheduler://foo?period=60s").to("bean:myBean?method=someMethodName");
The above route will generate an event and then invoke the
someMethodName method on the bean called myBean in the Registry such as JNDI or Spring.
And the route in Spring DSL:
<route> <from uri="scheduler://foo?period=60s"/> <to uri="bean:myBean?method=someMethodName"/> </route>
Forcing the scheduler to trigger immediately when completed
To let the scheduler trigger as soon as the previous task is complete, you can set the option greedy=true. But beware then the scheduler will keep firing all the time. So use this with caution.
Forcing the scheduler to be idle
There can be use cases where you want the scheduler to trigger and be greedy. But sometimes you want "tell the scheduler" that there was no task to poll, so the scheduler can change into idle mode using the backoff options. To do this you would need to set a property on the exchange with the key
Exchange.SCHEDULER_POLLED_MESSAGES to a boolean value of false. This will cause the consumer to indicate that there was no messages polled.
The consumer will otherwise as by default return 1 message polled to the scheduler, every time the consumer has completed processing the exchange.
