Exception Clause - Redelivery

Configuring RedeliveryPolicy (redeliver options)

RedeliveryPolicy requires to use the Dead Letter Channel as the Error Handler. Dead Letter Channel supports attempting to redeliver the message exchange a number of times before sending it to a dead letter endpoint. See Dead Letter Channel for further information about redeliver and which redeliver options exists.

No redelivery is default for onException

By default, any Exception Clause will not redeliver! (as it sets the maximumRedeliveries option to 0).

Sometimes you want to configure the redelivery policy on a per exception type basis. By default in the top examples, if an org.apache.camel.ValidationException occurs then the message will not be redelivered; however if some other exception occurs, e.g., IOException or whatever, the route will be retried according to the settings from the Dead Letter Channel.

However if you want to customize any methods on the RedeliveryPolicy object, you can do this via the fluent API. So lets retry in case of org.apache.camel.ValidationException up till two times.

  • Java

  • XML

  • YAML

onException(ValidationException.class)
    .maximumRedeliveries(2);
<onException>
    <exception>com.mycompany.ValidationException</exception>
    <redeliveryPolicy maximumRedeliveries="2"/>
</onException>
- onException:
    exception:
      - org.apache.camel.ValidationException
    redeliveryPolicy:
      maximumRedeliveries: 2

You can customize any of the RedeliveryPolicy options, for instance set a different delay of 5000 millis:

  • Java

  • XML

  • YAML

onException(ValidationException.class)
    .maximumRedeliveries(2).redeliveryDelay(5000);
<onException>
    <exception>com.mycompany.ValidationException</exception>
    <redeliveryPolicy maximumRedeliveries="2" redeliveryDelay="5000"/>
</onException>
- onException:
    exception:
      - org.apache.camel.ValidationException
    redeliveryPolicy:
      maximumRedeliveries: 2
      redeliveryDelay: 5000

Point of Entry for Redelivery Attempts

All redelivery attempts start at the point of the failure. So the route:

Java-only: redelivery starts at the point of failure
onException(ConnectException.class)
    .from("direct:start")
    .process("processor1")
    .process("processor2") // <--- throws a ConnectException
    .to("mock:theEnd")

Will retry from processor2 - not the complete route.

Asynchronous Delayed Redelivery

Camel has a feature to not block while waiting for a delayed redelivery to occur. However, if you use transacted routes then Camel will block as it’s mandated by the transaction manager to execute all the work in the same thread context. You can enable the non-blocking asynchronous behavior by the asyncDelayedRedelivery option. This option can be set on the errorHandler, onException or the redelivery policies.

By default, the error handler will create and use a scheduled thread pool to trigger redelivery in the future. You can also configure the executorServiceRef on the Error Handler to indicate a reference to either a shared thread pool you can enlist in the registry, or a thread pool profile in case you want to be able to control pool settings.

Catching Multiple Exceptions

Multiple exception can be caught as shown:

  • Java

  • XML

  • YAML

In Java DSL you can add multiple exceptions separated by comma.

onException(MyBusinessException.class, MyOtherBusinessException.class)
    .maximumRedeliveries(2)
    .to("activemq:businessFailed");

And in XML DSL you just add another exception element:

<onException>
    <exception>com.mycompany.MyBusinessException</exception>
    <exception>com.mycompany.MyOtherBusinessException</exception>
    <redeliveryPolicy maximumRedeliveries="2"/>
    <to uri="activemq:businessFailed"/>
</onException>

And in YAML DSL you just add another exception in the array:

- onException:
    exception:
      - com.mycompany.MyBusinessException
      - com.mycompany.MyOtherBusinessException
    redeliveryPolicy:
      maximumRedeliveries: 2
    steps:
      - to:
          uri: activemq:businessFailed
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