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.
For introduction and background material see Error handling in Camel.Exception Clause
Related to error handling is the Try Catch Finally as DSL you can use directly in your route. Its basically a mimic of the regular try catch finally in the Java language but with more power.
The current implementations Camel provides out of the box are:
- DefaultErrorHandler is the default error handler in Camel. This error handler does not support a dead letter queue, it will propagate exceptions back to the caller, as if there where no error handler at all. It has a limited set of features.
- Dead Letter Channel which supports attempting to redeliver the message exchange a number of times before sending it to a dead letter endpoint
LoggingErrorHandlerfor just catching and logging exceptions
NoErrorHandlerfor no error handling
- TransactionErrorHandler is the default error handler in Camel for transacted routes. 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
The Dead Letter Channel will redeliver at most 6 times using 1 second delay, and if the exchange failed it will be logged at
You can configure the default dead letter endpoint to use:
or also from Camel 2.3.0:
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.
or in Spring DSL:xml
or also from Camel 2.3.0:xml
This would create an error handler which logs exceptions using the category
mylogger.name and uses the level
INFO for all log messages created.
Loggers may also be defined for specific routes.
The no error handler is to be used for disabling error handling.java
or in Spring DSL:xml
or also from Camel 2.3.0:xml
The TransactionErrorHandler is the default error handler in Camel for transacted routes.[TransactionErrorHandler] is default for transacted routes
If you have marked a route as transacted using the
transacted DSL then Camel will automatic use a TransactionErrorHandler. It will try to lookup the global/per route configured error handler and use it if its a
TransactionErrorHandlerBuilder instance. If not Camel will automatic create a temporary TransactionErrorHandler that overrules the default error handler. This is convention over configuration.
Features Support by Various Error Handlers
Here is a breakdown of which features is supported by the Error Handler(s):
Supported By The Following Error Handler
See Exception Clause documentation for documentation of some of the features above.
The error handler is scoped as either
- per route
The following example shows how you can register a global error handler (in this case using the logging handler)
Spring Based ConfigurationJava DSL vs. Spring DSL
The error handler is configured a bit differently in Java DSL and Spring DSL. Spring DSL relies more on standard Spring bean configuration whereas Java DSL uses fluent builders.
The error handler can be configured as a spring bean and scoped in:
- global (the camelContext tag)
- per route (the route tag)
- or per policy (the policy/transacted tag)
The error handler is configured with the
The error handlers is inherited, so if you only have set a global error handler then its use everywhere. But you can override this in a route and use another error handler.
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
myDeadLetterErrorHandler that is our Dead Letter Channel. This configuration is standard Spring using the bean element.
Finally, we have another spring bean for the redelivery policy where we can configure the options for how many times to redeliver, delays etc.
TransactionalErrorHandler 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.
- Error handling in Camel for introduction and background material on error handling in Camel
- Dead Letter Channel for the dead letter error handler
- DefaultErrorHandler for the default error handler in Camel
- TransactionErrorHandler for the default error handler for transacted routes
- Transactional Client for transactional behavior
- Exception Clause as it supports handling thrown exceptions
- Try Catch Finally for try ... catch ... finally as DSL you can use in the routing