Chapter 44. Scheduler
Only consumer is supported
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.
44.1. 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 scheduler endpoints, only one scheduler thread pool and thread will be used - but you can configure the thread pool to allow more concurrent threads.
The IN body of the generated exchange is null. So exchange.getIn().getBody() returns null.
44.2. Configuring Options
Camel components are configured on two separate levels:
- component level
- endpoint level
44.2.1. Configuring Component Options
The component level is the highest level which holds general and common configurations that are inherited by the endpoints. For example a component may have security settings, credentials for authentication, urls for network connection and so forth.
Some components only have a few options, and others may have many. Because components typically have pre configured defaults that are commonly used, then you may often only need to configure a few options on a component; or none at all.
Configuring components can be done with the Component DSL, in a configuration file (application.properties|yaml), or directly with Java code.
44.2.2. Configuring Endpoint Options
Where you find yourself configuring the most is on endpoints, as endpoints often have many options, which allows you to configure what you need the endpoint to do. The options are also categorized into whether the endpoint is used as consumer (from) or as a producer (to), or used for both.
Configuring endpoints is most often done directly in the endpoint URI as path and query parameters. You can also use the Endpoint DSL as a type safe way of configuring endpoints.
A good practice when configuring options is to use Property Placeholders, which allows to not hardcode urls, port numbers, sensitive information, and other settings. In other words placeholders allows to externalize the configuration from your code, and gives more flexibility and reuse.
The following two sections lists all the options, firstly for the component followed by the endpoint.
44.3. Component Options
The Scheduler component supports 3 options, which are listed below.
| Name | Description | Default | Type |
|---|---|---|---|
| bridgeErrorHandler (consumer) | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. | false | boolean |
| autowiredEnabled (advanced) | Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. | true | boolean |
| poolSize (scheduler) | Number of core threads in the thread pool used by the scheduling thread pool. Is by default using a single thread. | 1 | int |
44.4. Endpoint Options
The Scheduler endpoint is configured using URI syntax:
scheduler:name
with the following path and query parameters:
44.4.1. Path Parameters (1 parameters)
| Name | Description | Default | Type |
|---|---|---|---|
| name (consumer) | Required The name of the scheduler. | String |
44.4.2. Query Parameters (21 parameters)
| Name | Description | Default | Type |
|---|---|---|---|
| bridgeErrorHandler (consumer) | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. | false | boolean |
| sendEmptyMessageWhenIdle (consumer) | If the polling consumer did not poll any files, you can enable this option to send an empty message (no body) instead. | false | boolean |
| exceptionHandler (consumer (advanced)) | To let the consumer use a custom ExceptionHandler. Notice if the option bridgeErrorHandler is enabled then this option is not in use. By default the consumer will deal with exceptions, that will be logged at WARN or ERROR level and ignored. | ExceptionHandler | |
| exchangePattern (consumer (advanced)) | Sets the exchange pattern when the consumer creates an exchange. Enum values:
| ExchangePattern | |
| pollStrategy (consumer (advanced)) | 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. | PollingConsumerPollStrategy | |
| synchronous (advanced) | Sets whether synchronous processing should be strictly used. | false | boolean |
| backoffErrorThreshold (scheduler) | The number of subsequent error polls (failed due some error) that should happen before the backoffMultipler should kick-in. | int | |
| backoffIdleThreshold (scheduler) | The number of subsequent idle polls that should happen before the backoffMultipler should kick-in. | int | |
| backoffMultiplier (scheduler) | 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. | int | |
| delay (scheduler) | Milliseconds before the next poll. | 500 | long |
| greedy (scheduler) | If greedy is enabled, then the ScheduledPollConsumer will run immediately again, if the previous run polled 1 or more messages. | false | boolean |
| initialDelay (scheduler) | Milliseconds before the first poll starts. | 1000 | long |
| poolSize (scheduler) | Number of core threads in the thread pool used by the scheduling thread pool. Is by default using a single thread. | 1 | int |
| repeatCount (scheduler) | Specifies a maximum limit of number of fires. So if you set it to 1, the scheduler will only fire once. If you set it to 5, it will only fire five times. A value of zero or negative means fire forever. | 0 | long |
| runLoggingLevel (scheduler) | The consumer logs a start/complete log line when it polls. This option allows you to configure the logging level for that. Enum values:
| TRACE | LoggingLevel |
| scheduledExecutorService (scheduler) | Allows for configuring a custom/shared thread pool to use for the consumer. By default each consumer has its own single threaded thread pool. | ScheduledExecutorService | |
| scheduler (scheduler) | To use a cron scheduler from either camel-spring or camel-quartz component. Use value spring or quartz for built in scheduler. | none | Object |
| schedulerProperties (scheduler) | To configure additional properties when using a custom scheduler or any of the Quartz, Spring based scheduler. | Map | |
| startScheduler (scheduler) | Whether the scheduler should be auto started. | true | boolean |
| timeUnit (scheduler) | Time unit for initialDelay and delay options. Enum values:
| MILLISECONDS | TimeUnit |
| useFixedDelay (scheduler) | Controls if fixed delay or fixed rate is used. See ScheduledExecutorService in JDK for details. | true | boolean |
44.5. 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.
44.6. Exchange Properties
When the timer is fired, it adds the following information as properties to the Exchange:
| Name | Type | Description |
|---|---|---|
|
|
|
The value of the |
|
|
| The time when the consumer fired. |
44.7. Sample
To set up a route that generates an event every 60 seconds:
from("scheduler://foo?delay=60000").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?delay=60000"/> <to uri="bean:myBean?method=someMethodName"/> </route>
44.8. 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.
44.9. 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.
44.10. Spring Boot Auto-Configuration
When using scheduler with Spring Boot make sure to use the following Maven dependency to have support for auto configuration:
<dependency>
<groupId>org.apache.camel.springboot</groupId>
<artifactId>camel-scheduler-starter</artifactId>
<version>{CamelSBProjectVersion}</version>
<!-- Use your Camel Spring Boot version -->
</dependency>The component supports 4 options, which are listed below.
| Name | Description | Default | Type |
|---|---|---|---|
| camel.component.scheduler.autowired-enabled | Whether autowiring is enabled. This is used for automatic autowiring options (the option must be marked as autowired) by looking up in the registry to find if there is a single instance of matching type, which then gets configured on the component. This can be used for automatic configuring JDBC data sources, JMS connection factories, AWS Clients, etc. | true | Boolean |
| camel.component.scheduler.bridge-error-handler | Allows for bridging the consumer to the Camel routing Error Handler, which mean any exceptions occurred while the consumer is trying to pickup incoming messages, or the likes, will now be processed as a message and handled by the routing Error Handler. By default the consumer will use the org.apache.camel.spi.ExceptionHandler to deal with exceptions, that will be logged at WARN or ERROR level and ignored. | false | Boolean |
| camel.component.scheduler.enabled | Whether to enable auto configuration of the scheduler component. This is enabled by default. | Boolean | |
| camel.component.scheduler.pool-size | Number of core threads in the thread pool used by the scheduling thread pool. Is by default using a single thread. | 1 | Integer |
