Error Handler

Error Handler

Camel supports pluggable ErrorHandler strategies to deal with errors processing an Event Driven Consumer. An alternative is to specify the error handling directly in the DSL using the Exception Clause.

Some current implementations include

• Dead Letter Channel which supports attempting to redeliver the message exchange a number of times before sending it to a dead letter endpoint
• LoggingErrorHandler for just catching and logging exceptions
• NoErrorHandler for no error handling
• Transaction for transactional error handling (Spring based). See the Transactional Client EIP pattern.

These error handlers can be applied in the DSL to an entire set of rules or a specific routing rule as we show in the next examples. Error handling rules are inherited on each routing rule within a single RouteBuilder

Short Summary of the provided Error Handlers

Default Error Handler (Dead Letter Channel)

The default error handler is the Dead Letter Channel which is automatically configured for you. By default Camel will redeliver at most 6 times using 1 second delay, and if the exchange failed it will be logged at ERROR level.

You can configure the default dead letter endpoint to use:

Logging Error Handler

The logging error handler will log (by default at ERROR level) whenever an uncaught exception is thrown. The logging category, logger and level may all be defined in the builder.

errorHandler(loggingErrorHandler("mylogger.name").level(LoggingLevel.INFO));

This would create an error handler which logs exceptions using the category mylogger.name and uses the level INFO for all log messages created.

from("seda:a").errorHandler(loggingErrorHandler("mylogger.name").level(LoggingLevel.DEBUG)).to("seda:b");

Loggers may also be defined for specific routes.

No Error Handler

The no error handler is to be used for disabling error handling.

errorHandler(noErrorHandler());

Setting global error handlers

The following example shows how you can register a global error handler (in this case using the logging handler)

Setting error handlers on a specific route

The following example shows how you can register a local error handler; the customized logging handler is only registered for the route from Endpoint seda:a

Spring based configuration

In Camel 1.4 the error handler can be configured as a spring bean and referenced as either:

• global (the camelContext tag)
• per route (the route tag)
• per policy (the policy tag)

The error handler is configured with the errorHandlerRef attribute.

Spring based configuration sample

In this sample we configure a Dead Letter Channel on the route that should redeliver at most 3 times and use a little delay before retrying.
First we configure the reference to myDeadLetterErrorHandler using the errorHandlerRef attribute on the route tag.

Then we configure myDeadLetterErrorHandler that is our Dead Letter Channel. This configuration is standard Spring using the bean element.
And finally we have another spring bean for the redelivery policy where we can configure the options for how many times to redeliver, delays etc.

Redelivery Policy

You can also configure the RedeliveryPolicy as this example shows

And configuration of the redelivery policy in Spring DSL is as:

Available as of Camel 1.5.1 or later
You can reference a RedeliveryPolicy so you can reuse existing configurations and use standard spring bean style configuration that supports property placeholders.

    <bean id="myRedeliveryPolicy" class="org.apache.camel.processor.RedeliveryPolicy">
        <property name="maximumRedeliveries" value="${myprop.max}"/>
    </bean>

     <onException>
         <!-- you can define multiple exceptions just adding more exception elements as show below -->
         <exception>com.mycompany.MyFirstException</exception>
         <exception>com.mycompany.MySecondException</exception>

         <!-- here we reference our redelivy policy defined above -->
         <redeliveryPolicy ref="myRedeliveryPolicy"/>
     </onException>

Using the transactional error handler

The transactional error handler is introduced in Camel 1.4 and is based on spring transaction. This requires the usage of the camel-spring component.
See Transactional Client that has many samples for how to use and transactional behavior and configuration with this error handler.

See also

The Dead Letter Channel for further details.
The Transactional Client for transactional behavior
The Exception Clause as it supports handling thrown exceptions