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Exception clauses is scoped as either:

• global
• or route specific

Where the global are the simplest and most easy to understand. In the advanced section we dig into the route specific and even combining them. However

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Camel uses DefaultExceptionPolicyStrategy to determine a strategy how an exception being thrown should be handled by which onException clause. The strategy is:

• the order in which the onException is configured takes precedence. Camel will test from first...last defined.
• Camel will start from the bottom (nested caused by) and recursive up in the exception hierarchy to find the first matching onException clause
• instanceof test is used for testing the given exception with the onException clause defined exception list. An exact instanceof match will always be used, otherwise the onException clause that has an exception that is the closets super of the thrown exception is selected (recurring up the exception hierarchy)

This is best illustrated with an exception:

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Using onException to handle known exceptions is a very powerful feature in Camel. However prior to Camel 1.5 you could not mark the exception as being handled, so the caller would still receive the caused exception as a response. In Camel 1.5 you can now change this behavior with the new handle DSL. The handle is a Predicate that is overloaded to accept three types of parameters:

• Boolean
• Predicate
• Expression that will be evaluates as a Predicate using this rule set: If the expressions returns a Boolean its used directly. For any other response its regarded as true if the response is not null.

For instance to mark all ValidationException as being handled we can do this:

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You can define exception clauses either as:

• global
• or route specific

We start off with the sample sample that we change over time. First off we use only global exception clauses:

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