I guess that if you want to handle exceptions in a JBI compliant way,
you should put in the flow some specific components to do that.
First, we need to make a distinction between faults and errors.
Imho, faults are unrecoverable problems, due to the message itself.
Errors are runtime problems, which may be able to be solved at
a later time.
In your example, depending on the reason why the data could not be
stored in the database, the component should return a fault
(if the data is corrupted) or an error (the database is down).
In your use case, the error should be catched by a simple component
(an EIP pattern) between the http component and the business
component which would act as a normal proxy when no errors are
reported, and redirect the flow elsewhere when an error occurs.
Also, I don't really understand the "friendly error" concept ;)
The http component is not designed to be a jsp server, so you
won't have any nice interface there. The output should be an xml.
If you want a nice interface, you should deploy a web app which
would call the jbi bus and return a nice html page when an error
occurs.
Last, while I think declarative transactions may be really useful
for POJO based components (servicemix-jsr181, or the yet to be
defined new component, see other threads on the list),
it would be difficult to apply it in a real JBI world.
Let's discuss it, it' s just my thoughts.
On 8/25/06, jpuro <[EMAIL PROTECTED]> wrote:
I think it would be useful to add declarative exception handling to
ServiceMix. The usefullness of such a feature can be seen from the
following simple use case involving a client submitting an order to a
fulfillment company:
1) The use case starts when the client sends an order to an HTTP endpoint
exposed in ServiceMix. The message representing the order is routed to a
business service component.
2) The business service component attempts to process the Order and save
it
to a database. However, an exception occurs during this process and gets
bubbled up. The fulfillment company would like to be notified via email
when an order fails to be processed. Since we have configured the
business
service component to pass all exceptions to an email component, the flow
moves to step 3.
3) The email component sends out an email notification to the fulfillment
company indicating that an error occurred while processing the order.
4) After the email has been sent out, the flow moves to another component
that returns a more user friendly error message to the original HTTP
endpoint. This way we do not send back a hard to read error message to
the
client.
The purpose of such a flow is that we handle exceptions more gracefully
than
currently is supported by ServiceMix. Instead of bubbling up exceptions
to
the calling component, we should allow components to change the flow of a
message when an exception occurs.
The configuration could look something like the following:
<activationSpec componentName="businessServiceComponent"
service="example:businessService"
exceptionDestionationService="example:emailService">
<sm:component>
<bean class="com.mycompany.MyClass
"/>
</sm:component>
</activationSpec>
Alternatively, perhaps we can just use AOP to catch exceptions that occur
within a component:
<sm:exceptionHandler
exceptionType="javax.jbi.messaging.MessagingException"
destinationService="example:emailService">
<activationSpec componentName="businessServiceComponent"
service="example:businessService">
<sm:component>
<bean class="
com.mycompany.MyClass"/>
</sm:component>
</activationSpec>
</sm:exceptionHandler>
Here are a few concerns of mine:
1) The problem with the first example configuration is that it doesn't
allow you to get creative with how certain types of exceptions are
handled,
it just acts like a catch all. We may need to create a more flexible way
of
configuring exception handling.
2) Because of the way JBI service units/assemblies are packaged and
deployed, would this work? Is there any discussion on declaratively
handling exceptions in the JBI spec?
Regards,
Jeff
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Cheers,
Guillaume Nodet
