THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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.
For introduction and background material see Error handling in Camel.
| Info | ||
|---|---|---|
| ||
In Camel 2.0 onwards there default error handler is changed from Dead Letter Channel to DefaultErrorHandler. This error handler does not support a dead letter queue and will return exceptions back to the caller. This is what you expects when working with regular Java that exceptions will be thrown back to the caller. This error handler supports a limited set of features. |
...
Using Error Handler combined with Exception Clause is a very powerful
...
combination. We encourage end-users to use this combination in your error handling strategies. See samples and 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:
Non-transacted:
- DefaultErrorHandler is the default error handler in Camel 2.0 onwards. This error handler does not support a deal 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 exceptionsNoErrorHandlerfor no error handling
Transacted:
- TransactionErrorHandler is the default error handler in Camel 2.0 onwards for transacted routes. This error handler does not support a deal 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.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
...
...
If the route is transactional then the Dead Letter Channel is disabled. The exchange.isTransacted() is used to determine if an Exchange is transacted or not.
So if you are using transacted routes then you should configure the TransactionErrorHandler instread of DeadLetterChannel. See Transactional Client for further details and samples.
Short Summary of the
...
Provided Error Handlers
DefaultErrorHandler
...
The DefaultErrorHandler is the new default error handler in Camel 2.0. It only supports a limited set of features such as catching exception and using the Exception Clause. It does not support redelivery, delays or the likes. It will propagate exceptions back to the original caller. It . Unlike Dead Letter Channel it does not have any dead letter queue, and do not handle exceptions by default.
Dead Letter Channel
The Dead Letter Channel is the default error handler in Camel 1.x, 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 at ERROR level.
You can configure the default dead letter endpoint to use:
...
...
or in Spring DSL:
...
or also from Camel 2.3.0:
...
The LoggingErrorHandler
...
The logging error handler will log (by default at 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:
...
or also from Camel 2.3.0:
...
This would create an error handler which logs exceptions using the category category mylogger.name and uses the level level INFO for all log messages created.
...
Loggers may also be defined for specific routes.
...
The NoErrorHandler
The no error handler is to be used for disabling error handling.
...
TransactionErrorHandler new in Camel 2.0
or in Spring DSL:
...
or also from Camel 2.3.0:
...
TransactionErrorHandler
The TransactionErrorHandler is the new default error handler in Camel 2.0 for transacted routes. It only supports a limited set of features such as catching exception and using the Exception Clause. It does not support redelivery, delays or the likes. It will propagate exceptions back to the original caller. It does not have any dead letter queue.
...
...
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):
See Exception Clause documentation for documentation of some of the features above.
Scopes
The error handler is scoped as either
- global
- per route
The following example shows how you can register a global error handler (in this case using the logging handler)
...
...
The following example shows how you can register a route specific error handler; the customized logging handler is only registered for the route from Endpoint seda:a
...
Spring
...
Available as of Camel 1.4
...
Based Configuration
...
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.
In Camel 1.4 the 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 errorHandlerRef attribute.
...
...
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 to myDeadLetterErrorHandler using the errorHandlerRef attribute on the route tag.
...
...
Then we configure configure myDeadLetterErrorHandler that is our Dead Letter Channel. This configuration is standard Spring using the bean element.
And finally Finally, we have another spring bean for the redelivery policy where we can configure the options for how many times to redeliver, delays etc.
...
Using
...
the TransactionalErrorHandler
The TransactionalErrorHandler 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
...
- 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