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In Camel we prefix the keywords with do
to avoid having same keyword as Java. So we have:
doTry
doCatch
doFinally
end
to end the block in Java DSL
Notice this document is based on how it works in Camel 2.0. In Camel 1.x this feature isn't as powerful and it uses a slight different keyword names.
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When using doTry .. doCatch .. doFinally
then the regular Camel Error Handler does not apply. That means any onException
or the likes does not trigger. The reason is that doTry .. doCatch .. doFinally
is in fact its own error handler and that it aims to mimic and work like how try/catch/finally works in Java.
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The doCatch
in Camel is empowered over its Java sister.
First of all you can define multiple exceptions to catch in a single block.
And second of all an important aspect over the regular Java counter parts is that Camel will check in the exception hierarchy when it matches a thrown exception against the doCatch
blocks. The reasons is that many times the original caused exceptions is wrapped by other wrapper exceptions, typically transposing the exception from a checked to a runtime exception.
Camel for instance does this by wrapped it in a CamelRuntimeException
. So if the original caused exception is an java.io.IOException
then Camel will still match a doCatch
block defined with an java.io.IOException
. And just like Java the order in which you have multiple doCatch
blocks matter. Camel will iterate from the top going down and use the first doCatch
that matches the exception. The reason is to keep it similar to the regular java and how it selects a catch block. This differers from the Exception Clause that has a more intelligent exception selection strategy among multiple onException
definitions, where it also consider the delta in the exception hierarchy to select the best definition.
A third feature is that . And secondly you can attach a onWhen
predicate to signal if the catch should trigger or not at runtime.
To And to simulate rehrowing rethrowing an exception from a doCatch
you should use the handled
predicate. If its evaluated to false
Camel will reattach the exception on the Exchange. And just like Java the order in which you have multiple doCatch
blocks matter. Camel will iterate from the top going down and use the first doCatch
that matches the exception and if the onWhen
predicate matches as well (if any provided). This is the same behavior as the Exception Clause
Using try .. catch .. finally in Java DSL
In the route below we have all keywords in action. As the code is based on a unit test we route using Mock.
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And in the route below we want to indicate if an IOException occured we want to route it elsewhere and at the same time keep the exception so the original caller is notified about this exception. To do this we need to not rethrow the exception and this is why we use handled and set it to false to indicate, no we did not handle it so please keep the exception.
The 2nd exception block can be omitted but as the code is based on an unit test we want to test the behavior non IOException
as well.
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And finally we have an example of the onWhen
predicate in action. We can attach it to a doCatch
block and at runtime determine if the block should be triggered or not.
In our case we only want to trigger if the caused exception message contains the damn word.
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Notice when using Java DSL we must use end()
to indicate where the try .. catch .. finally block ends. As the example above has a finally, then the end()
should be at the end of the finally block. If we are not using a finally, then the end()
should be at the end of the doCatch
to indicate the end there.
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Using try .. catch .. finally in
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Spring DSL
We show the three sample samples using Spring DSL instead.
In the route below we have all keywords in action. As the code is based on a unit test we route using Mock.
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And in the route below we want to indicate if an IOException occured we want to route it elsewhere and at the same time keep the exception so the original caller is notified about this exception. To do this we need to not rethrow the exception and this is why we use handled and set it to false to indicate, no we did not handle it so please keep the exception.
The 2nd exception block can be omitted but as the code is based on an unit test we want to test the behavior non IOException
as well.
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And finally we have an example of the onWhen
predicate in action. We can attach it to a doCatch
block and at runtime determine if the block should be triggered or not.
In our case we only want to trigger if the caused exception message contains the damn word.
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