Spring integration finally type handler

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I have an application which reads from a kafka queue and and goes on like this.

validate->convert->enrich->persist->notify

In the flow, I'm gathering some performance and other data points into a ThreadLocal container.

In the happy scenario I'm sending these information to a service to be later used in reporting. But the pipeline can stop in any step if one of the step fails due to a known error (eg, convert failed so flow should stop there). I do not like each of these processors to have a code that sends the information in the ThreadLocal to reporting service if the execution resulted in error, as that would couple those services with information not related to its task.

It would be nice to have a way to execute a service at the end of the flow to send this information out, no matter which step the pipeline stops moving forward. Also there could be scenarios some code did throw an exception that was not known or other issue that break the flow.

Is there a way that a final operation to be executed no matter the result of the pipeline so that it can be used to send this information similar to a finally block in java?

spring-integration spring java
1 Answers

The integration flow is like a simple Java try...catch...finally. It is really more about a distributed computation and loosely-coupling principle between components. So, even if you tie endpoints with channels in between, there really have nothing to know about the previous and next step: everything is done in the current endpoint with its input and output channels. Therefore your request about something like finally in the flow does not fit to the EIP concepts and cannot be implement as some primitive in the framework.

You are just lucky in your use-case that you can rely on the ThreadLocal for your flow logic, but you should keep in mind that it is not a way to deal with messaging. It really has to be stateless and have scope only of the message traveling from one endpoint to another. Therefore it might be better to revise your logic in favor of storing such a tracing information into headers of that message on each step. This way in the future you can make the flow fully async or even distributed in the network.

This is just my concern for a design you have so far.

For the current error handling problem consider to have that "final" step behind some well-know channel, so you will be free to send a message to that endpoint from whatever place you need. For example you can wrap problematic endpoints into an ExpressionEvaluatingRequestHandlerAdvice. Handle an error over there and send it to the mentioned channel. This way your business method will be free from error handling and so. See more in docs: https://docs.spring.io/spring-integration/docs/current/reference/html/messaging-endpoints.html#expression-advice

If your flow starts from some gateway or inbound channel adapter, you can have an errorChannel configured there to be able to catch all the downstream errors in one central place. And again: send the handling result to the mentioned channel.

But no. No finally in the framework at the moment and I doubt it would even be suitable in the future. For the messaging and async reason I explained before.

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