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Chapter 23. Cron

Only consumer is supported

The Cron component is a generic interface component that allows triggering events at specific time interval specified using the Unix cron syntax (e.g. 0/2 * * * * ? to trigger an event every two seconds).

Being an interface component, the Cron component does not contain a default implementation, instead it requires that the users plug the implementation of their choice.

The following standard Camel components support the Cron endpoints:

  • Camel-quartz
  • Camel-spring

The Cron component is also supported in Camel K, which can use the Kubernetes scheduler to trigger the routes when required by the cron expression. Camel K does not require additional libraries to be plugged when using cron expressions compatible with Kubernetes cron syntax.

23.1. Dependencies
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When using cron with Red Hat build of Camel 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-cron-starter</artifactId>
</dependency>

Additional libraries may be needed in order to plug a specific implementation.

23.2. Configuring Options
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Camel components are configured on two levels:

  • Component level
  • Endpoint level

23.2.1. Component Level Options
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The component level is the highest level. The configurations you define at this level are inherited by all the endpoints. For example, a component can have security settings, credentials for authentication, urls for network connection, and so on.

Since components typically have pre-configured defaults for the most common cases, you may need to only configure a few component options, or maybe none at all.

You can configure components with Component DSL in a configuration file (application.properties|yaml), or directly with Java code.

23.2.2. Endpoint Level Options
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At the Endpoint level you have many options, which you can use to configure what you want the endpoint to do. The options are categorized according to whether the endpoint is used as a consumer (from) or as a producer (to) or used for both.

You can configure endpoints directly in the endpoint URI as path and query parameters. You can also use Endpoint DSL and DataFormat DSL as type safe ways of configuring endpoints and data formats in Java.

When configuring options, use Property Placeholders for urls, port numbers, sensitive information, and other settings.

Placeholders allows you to externalize the configuration from your code, giving you more flexible and reusable code.

23.3. Component Options
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The Cron component supports 3 options, which are listed below.

Expand
NameDescriptionDefaultType

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

cronService (advanced)

The id of the CamelCronService to use when multiple implementations are provided.

 

String

23.4. Endpoint Options
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The Cron endpoint is configured using URI syntax: 

cron:name

with the following path and query parameters:

23.4.1. Path Parameters (1 parameters)
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Expand
NameDescriptionDefaultType

name (consumer)

Required The name of the cron trigger.

 

String

23.4.2. Query Parameters (4 parameters)
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Expand
NameDescriptionDefaultType

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

schedule (consumer)

Required A cron expression that will be used to generate events.

 

String

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:

  • InOnly
  • InOut
  • InOptionalOut
 

ExchangePattern

23.5. Usage
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The component can be used to trigger events at specified times, as in the following example: 

from("cron:tab?schedule=0/1+*+*+*+*+?")
.setBody().constant("event")
.log("${body}");

The schedule expression 0/3+10+*+? can be also written as 0/3 10 * * * ? and triggers an event every three seconds only in the tenth minute of each hour.

Parts in the schedule expression means (in order):

  • Seconds (optional)
  • Minutes
  • Hours
  • Day of month
  • Month
  • Day of week
  • Year (optional)

Schedule expressions can be made of 5 to 7 parts. When expressions are composed of 6 parts, the first items is the "seconds" part (and year is considered missing).

Other valid examples of schedule expressions are:

  • 0/2 * * * ? (5 parts, an event every two minutes)
  • 0 0/2 * * * MON-FRI 2030 (7 parts, an event every two minutes only in year 2030)

Routes can also be written using the XML DSL. 

<route>
    <from uri="cron:tab?schedule=0/1+*+*+*+*+?"/>
    <setBody>
      <constant>event</constant>
    </setBody>
    <to uri="log:info"/>
</route>

23.6. Spring Boot Auto-Configuration
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The component supports 4 options, which are listed below.

Expand
NameDescriptionDefaultType

camel.component.cron.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.cron.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.cron.cron-service

The id of the CamelCronService to use when multiple implementations are provided.

 

String

camel.component.cron.enabled

Whether to enable auto configuration of the cron component. This is enabled by default.

 

Boolean

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