Reinstate support for auto-configuring an embedded ActiveMQ broker

[mattrpav]

#38404

[wilkinsona]

How's it going, @mattrpav? Do you still have plans to finish this off?

[mattrpav]

@wilkinsona Thanks for the ping. Yes, I plan to get this wrapped up. What is the timeframe to make it in the next Spring Boot release?

[scottfrederick]

@mattrpav Since this would be considered a feature addition, we would only add it in a new minor release. The next scheduled minor release is 3.4 in November of this year. There will be several milestone releases and a release candidate leading up to the minor version release, which would give users a chance to try it out.

[snicoll]

@mattrpav I've looked at what you've done and there's the question of whether we want to reinstate the behavior as it was before. To figure that out, I am happy to look at the various options and polish your proposal. Are you ok with that? We'd like to make sure you haven't wasted time on this.

[mattrpav]

@snicoll I have the WIP PR at about 80% and I'll have time to wrap this up soon. A couple ActiveMQ upstream releases are wrapping up, so I can turn my attention to finish this.

Generally, it would seem that providing the like-for-like would ease transition for spring-jms users to make the javax.* to jakarta.* transition. At the same time, improvements always sound compelling, what did you have in mind? Can these be done side-by-side with the existing capabilities and property flags?

I'm hearing from a lot of users that are waiting for this to make the transition to Jakarta-based Spring. A lot of folks have long time investments in ActiveMQ and the other alternatives do not suit their needs.

[snicoll]

I have the WIP PR at about 80%

Can you push the code then?

At the same time, improvements always sound compelling, what did you have in mind? Can these be done side-by-side with the existing capabilities and property flags?

I didn't mention improvements. It's figuring out how we get from what we have to this. Right now, Spring Boot 3.x users of ActiveMQ with no configuration would get an infrastructure that connects to an existing broker on localhost using tcp. After this change, it would use an embedded broker in memory. This can be very surprising and we're wondering if that's what we should be doing.

[snicoll]

@mattrpav is this PR ready for review now?