I’m curious: could we use direct instantiation based on classpath detection instead of introducing this factory abstraction?

For instance, Spring Kafka’s MessagingMessageConverter handles Jackson version selection via classpath detection:

https://github.com/spring-projects/spring-kafka/blob/fcca99f6ae3d4f370817cfd1e24f2ae5db93efbf/spring-kafka/src/main/java/org/springframework/kafka/support/converter/MessagingMessageConverter.java#L93-L105

Since we already have JacksonPresent too, could we apply the same pattern here so version selection is automatic and users don’t have to manually choose? If there’s a downside or constraint in our case, what is it?

I was thinking that people can extend AbstractMessageConverterFactory and do their own implementation of MessageConverter. Also, it is much more readable when I refactored to this way considering deletions and so on.

Hey @MatejNedic, I understand what you're aiming at, and we already support users providing their own MessageConverters through the SqsListenerConfigurer.

As far as I can tell, the only place we're using the create() method from AbstractMessageConverterFactory is in AbstractListenerAnnotationBeanPostProcessor.java:345.

I think we could just detect the Jackson version on the classpath there and decide what converter to use automatically.

This might eliminate the need for AbstractMessageConverterFactory, JacksonJsonMessageConverterFactory, and LegacyJackson2MessageConverterFactory, and make overall converter configuration simpler, while still preserving the customization options for users.

What do you think?

Hey @tomazfernandes , I was thinking about it but I came up with following scenario.

What if you have Jackson 3 and Jackson 2 on classpath. Since this is messaging I want to keep Jackson 2 for SQS integration. currently if we put JacksonPresent users are not able to change this behaviour.

Notice inside of SqsListenerAnnotationBeanPostProcessor we are also based on instace getting ObjectMapper or JsonMapper. I want to allow users to control this. I don't also want to polute EndpointRegistar with ObjectMapper and JsonMapper (we had objectMapper there). So for me best way was to do a wrapper and then extract either Jackson 2 or Jackson 3 based on whichever Bean users defined. This allows users themselves to have on Classpath Jackson 3 and 2 and opt in for 2.

if (wrapper instanceof JacksonJsonMessageConverterFactory) {
			argumentResolvers.add(new NotificationMessageArgumentResolver(messageConverter,
					((JacksonJsonMessageConverterFactory) wrapper).getJsonMapperWrapper().getJsonMapper()));
			argumentResolvers.add(new NotificationSubjectArgumentResolver(
					((JacksonJsonMessageConverterFactory) wrapper).getJsonMapperWrapper().getJsonMapper()));
			argumentResolvers.add(new SnsNotificationArgumentResolver(messageConverter,
					((JacksonJsonMessageConverterFactory) wrapper).getJsonMapperWrapper().getJsonMapper()));
		}
		else if (wrapper instanceof LegacyJackson2MessageConverterFactory) {
			argumentResolvers.add(new LegacyJackson2NotificationMessageArgumentResolver(messageConverter,
					((LegacyJackson2MessageConverterFactory) wrapper).getObjectMapper()));
			argumentResolvers.add(new LegacyJackson2NotificationSubjectArgumentResolver(
					((LegacyJackson2MessageConverterFactory) wrapper).getObjectMapper()));
			argumentResolvers.add(new LegacyJackson2SnsNotificationArgumentResolver(messageConverter,
					((LegacyJackson2MessageConverterFactory) wrapper).getObjectMapper()));
		}

	@tomazfernandes Wdyt?

I want to allow users to control this.

If the goal is to enable users to force Jackson 2 over Jackson 3 when both are present, a more consistent approach would be exposing this as an option on the EndpointRegistrar, so users can explicitly toggle it via SqsListenerConfigurer. For example JacksonVersion {AUTO, JACKSON_2, JACKSON_3} or something similar. We can also expose the same option as an auto-configuration property if we’d like.

This way we rely on the existing configuration path instead of introducing a new one, and we don’t require users to declare a bean just to flip a configuration toggle. It also makes the selection explicit user intent and keeps the wiring simpler.

If it helps unblock the release we can make this PR focused on the default behavior only (no factory, detect Jackson 2 vs 3, if both are present default to Jackson 3), and add the explicit opt-in toggle in a separate PR.

Let me know your thoughts.

Hey @MatejNedic, can you share the exact 3.x scenario you're referring to, ideally a snippet?

Thanks.

I can completely rework this for RC1.

@MatejNedic, appreciate you reworking this for RC1.

For the set later behavior with ObjectMapper, we can keep the 3.x wiring, with both Jackson 2's ObjectMapper (when present) alongside Jackson's 3 JsonMapper in the EndpointRegistrar, and build the appropriate converter.

Let me know if you run into any issues.

@MatejNedic, after looking more closely at the classpath and classloading implications, I think this path could introduce CNFE/classpath edge cases across certain dependency combinations, including native/AOT setups.

I also think the current implementation has similar risk: some code paths (for example, instanceof checks against Jackson-specific impl classes) may trigger eager loading/linking of those impls, which can fail when the relevant Jackson dependency is not present.

If timeline allows, I’d prefer releasing this as an M2 so we have room to iterate and gather feedback before RC/GA. If RC1 is the priority, I’m ok shipping as-is and then reassessing for an RC2 if needed.

@tomazfernandes let's release it as RC1. I believe this solution is good as it is even for GA - the mentioned factory class should be deprecated from the start as this is anyway only intermediary solution for backward compatibility with Jackson 2.

Of course, if we have ideas and capacity to implement a better one, we could do it, but seems like time flies faster than we are able to catch up.

Are you able to give more specific places in code that can introduce CNFE? (I don't see it but i might have missed it).

@maciejwalkowiak agreed on RC1.

While Matej's refactor addressed the instanceof CNFE concerns, I've made some review comments that point out a few remaining points.

the mentioned factory class should be deprecated from the start as this is anyway only intermediary solution for backward compatibility with Jackson 2

Agreed. Let's reflect that in the code by marking it as deprecated and renaming it to something more migration-scoped to make the long-term direction clearer.

See comment about the javadoc above.

With this diff we're removing the ability for the user to set their own mapper in the converter through direct configuration.

I suggest that instead we make it so that if the user sets a JsonMapper, we'll use that to create a new JacksonJsonMessageConverter with the default settings, and then follow a similar path to the current one.

User should pass objectMapper through the factory. Since now Factory objectMapper is used to be set later on MessageConverter.

Thing is I don't want in this class anything Jackson 2 or Jackson 3 specific. That is why I went with Factroy approach to completely remove any Jackson 2 or 3 classes from here.

In JacksonJsonMessageConverter for Jacskon 3 we cannot set JsonMapper after Converter is created that is why I moved it to factory creation as well so JsonMapper user passed is respected.

User should pass objectMapper through the factory. Since now Factory objectMapper is used to be set later on MessageConverter.

This is not true for user-instantiated converters, users need a way to manually set it.

Thing is I don't want in this class anything Jackson 2 or Jackson 3 specific.

We can move this method (and the one for the JsonMapper) to the respective subclasses.