Apache Camel: errorHandler vs onException?

Question

What's the difference between:

<camel:errorHandler id="deadLetterErrorHandler" type="DeadLetterChannel" 
        deadLetterUri="log:dead">

<camel:camelContext errorHandlerRef="deadLetterErrorHandler">
    ...
</camel:camelContext>

And:

<onException>
    ...
</onException>

According to this article, using them both in conjunction is a "powerful combination". How so? What roles do they each individual assume, and how do they complement each other?

score 27 · Accepted Answer · answered Jun 27 '13 at 15:32

27

The errorHandler is used to handle any uncaught Exception that gets thrown during the routing and processing of a message. Conversely, onException is used to handle specific Exception types when they are thrown. Check out this article to see how to use onException.

answered Jun 27 '13 at 15:32

Keith

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So if I write `onException(Throwable.class)` I've basically implemented the `errorHandler`? – DavidS Aug 02 '17 at 17:49
I'm new to camel but as for me it lacks support for per-processor error handler - handler that will catch any exception. Sample code: ~~~
from("direct:a") .unmarshall(new MyDataFormat("param1")) .perProcessorErrorHandler(deadLetterQueue("log:foo")) .process(myProcessor) .perProcessorErrorHandler(deadLetterQueue("log:bar")) .to(myAnotherProcessor) .perProcessorErrorHandler(deadLetterQueue("log:baz")) ~~~ this allows me not to think about types of exceptions for each processor
– pls Sep 02 '22 at 06:35

score 4 · Answer 2 · answered Jun 28 '13 at 08:30

If the action you need to perform for each type of exception is different, use onException. It lets you define error handling on a per exception basis.

onException(xxxException.class).to("activemq:xxxFailed"); onException(yyyException.class).to("activemq:yyyFailed");

If you just need a generic handler, go with errorHandler. For all type of errors, the same processing will be performed.

Apache Camel: errorHandler vs onException?

2 Answers2