handling exceptions for Http rest endpoints in spring integration - spring-integration

Question

I need to throw an exception to the end user, can you please assist with this?
<int-http:request-handler-advice-chain>
<!--<bean class="org.springframework.integration.handler.advice.RequestHandlerRetryAdvice">
<property name="recoveryCallback">
<bean class="org.springframework.integration.handler.advice.ErrorMessageSendingRecoverer">
<constructor-arg ref="retryErrorChannel" />
</bean>
</property>
<property name="retryTemplate" ref="retryLoadTemplate" />
</bean>-->
<bean class="org.springframework.integration.handler.advice.ExpressionEvaluatingRequestHandlerAdvice">
<property name="successChannel" ref="afterSuccessFetchChannel" />
<property name="failureChannel" ref="afterFailFetchChannel" />
</bean>
</int-http:request-handler-advice-chain>
</int-http:outbound-gateway>
<int:transformer ref="testTransformer" method="processDetails" />
<int:transformer input-channel="afterSuccessFetchChannel" output-channel="goodResultChannel"
expression="'Fetching load id: ' + payload + ' details was successful'" />
<int:transformer input-channel="afterFailFetchChannel" output-channel="badResultChannel"
expression="payload + ' was bad, with reason: ' + payload.cause.message" />
<int:logging-channel-adapter id="badResultChannel" level="ERROR"/>
<int:logging-channel-adapter id="goodResultChannel" level="INFO" />
How and where to handle custom exceptions and how to re throw them?
My api is throwing 404 Not found exception, need to catch and re throw it to the user?
for now, I am just using logging channel, I don't really know the way to deal with exceptions in spring integration, can you please help?

Answer 1

So, instead of that <int:logging-channel-adapter id="badResultChannel" level="ERROR"/> you just need to write some POJO method which would throw some other exception after its handling. The ExpressionEvaluatingRequestHandlerAdvice has this property returnFailureExpressionResult to be set to true.
The logic is like this:
try {
evalResult = this.onFailureExpression.getValue(prepareEvaluationContextToUse(exception), message);
}
catch (Exception e) {
evalResult = e;
logger.error("Failure expression evaluation failed for " + message + ": " + e.getMessage());
}
and then:
if (this.onFailureExpression != null) {
Object evalResult = evaluateFailureExpression(message, actualException);
if (this.returnFailureExpressionResult) {
return evalResult;
}
}
So, your custom thrown exception is going to be sent as a reply message payload back to the caller. And there probably an MVC layer can simply convert it to respective HTTP response for the client.