Why is Mule exception strategy so chatty? - exception

Question

In my Mule app, I've configured some of the flows to use a catch exception strategy in order to do some special processing. For these cases, I want to pop the error and the original payload into an object store. Everywhere else, the default exception strategy is fine.
<flow name="saveLookup">
<vm:inbound-endpoint exchange-pattern="one-way" ref="Lookup_Save_VM" />
<component>
<spring-object bean="insertLookupMDCvalues"/>
</component>
<set-variable variableName="originalPayload" value="#[payload]"/>
<json:json-to-object-transformer returnClass="com.company.LookupData"/>
<set-variable variableName="transactionId" value="#[payload.transactionId]"/>
<transactional action="ALWAYS_BEGIN">
<logger message="${lookup.SQL}" level="INFO"/>
<jdbc:outbound-endpoint exchange-pattern="request-response" queryKey="saveLookup" queryTimeout="-1" connector-ref="JdbcConnector" />
<foreach collection="#[payload.transactional.lookupItems.items]">
<logger message="${lookup.item.SQL}" level="INFO" />
<jdbc:outbound-endpoint exchange-pattern="request-response" queryKey="saveLookupItem" queryTimeout="-1" connector-ref="JdbcConnector"/>
</foreach>
</transactional>
<component>
<spring-object bean="clearLookupMDCvalues"/>
</component>
<catch-exception-strategy>
<message-properties-transformer scope="invocation">
<add-message-property key="errorMap" value="#[['id' : transactionId, 'body' : originalPayload, 'error' : exception.summaryMessage]]"/>
</message-properties-transformer>
<choice>
<when expression="#[message.inboundProperties['resubmit']]">
<logger message="Resubmission of lookup data failed, saving to Dead Letter object store. ID=#[transactionId]" level="INFO"/>
<objectstore:store config-ref="lookupDeadLetterOS" key="#[transactionId]" overwrite="true" value-ref="#[errorMap]"/>
</when>
<otherwise>
<logger message="Saving lookup data failed, saving to Error object store. ID=#[transactionId]" level="INFO"/>
<objectstore:store config-ref="lookupErrorOS" key="#[transactionId]" overwrite="true" value-ref="#[errorMap]"/>
</otherwise>
</choice>
<set-payload value="Error: #[exception.summaryMessage]"/>
<component>
<spring-object bean="clearLookupMDCvalues"/>
</component>
</catch-exception-strategy>
</flow>
My problem is that when an error is encountered, let's say a Null Pointer Exception in the foreach component, I'm seeing four ERROR log statements for each event:
Exception stack is: 1. null (java.lang.NullPointerException) ...and so on. This is logged twice.
CatchMessagingExceptionStrategy - Message : Execution of the expression "payload.transactional.lookupItems.items" failed. (org.mule.api.expression.ExpressionRuntimeException). Message payload is of type: LookupData
DefaultMessagingExceptionStrategy - Message : Execution of the expression "payload.transactional.lookupItems.items" failed. (org.mule.api.expression.ExpressionRuntimeException). Message payload is of type: LookupData
I thought that a flow-specific exception strategy should override the default strategy. Why the duplicate log messages, and is there a way to shush them? I'd like to avoid having to configure the default exception strategy, as it's perfectly acceptable behavior in the majority of the flows.

Answer 1

The issue is that the built in exception strategies inherit from AbstractExceptionListener, and they all use the logException template method. The base implementation always logs at ERROR level, which is sometimes not appropriate for your application.
You can create a simple subclass of CatchMessagingExceptionStrategy that overrides the logException method, and logs however you want. Then, use it in your flow in place of the <catch-exception-strategy> like so:
<custom-exception-strategy class="com.mycompany.mule.QuietCatchExceptionStrategy">
<!-- your message processors here -->
</custom-exception-strategy>