Consider if ContainerType.SIMPLE should be the default in RabbitProperties

[philwebb]

See comment here.

It's not clear to me if we should change the value or update the Javadoc.

[philwebb]

/cc @garyrussell

[garyrussell]

Unfortunately, it's not black and white - each container has certain pros and cons. I feel that changing the container type without the user explicitly choosing to do so could cause unexpected problems for users.

I prefer that the user explicitly opt-in to using the new container. Documentation here.

[snicoll]

@garyrussell what puzzles me is that I think I've seen the term "legacy" to refer to the simple container. Is it reasonable that 2.0 default to something that's legacy? Are you going to remove it in a future release?

[garyrussell]

Perhaps legacy was a poor choice of words; I simply wanted to convey that simple refers to the old, existing, container. There are no plans to remove it.

Perhaps we should change the enum javadocs (in RabbitProperties) to:

 +		/**
 +		 * SimpleMessageListenerContainer - container where the RabbitMQ consumer
 +		 * dispatches messages to an invoker thread.
 +		 */
 +		SIMPLE,

(i.e. just drop the word legacy).

BTW, the reason I repeated the above comment on the PR as well is so the original poster of the comment would get a notification.

[wilkinsona]

Done. Thanks for the suggestion, @garyrussell