Auto-configure BatchMessagingMessageConverter with Listener.Type.Batch

[leochans]

when use batch type listener, simply declare a bean of RecordMessageConverter will not effect, should warp the RecordMessageConverter to a BatchMessagingMessageConverter when use batch type listener

[pivotal-issuemaster]

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[snicoll]

paging @garyrussell

[garyrussell]

@snicoll Functionally LGTM but there are code formatting violations.

It also needs a couple of tests - one with, and one without a configured RecordMessageConverter @Bean - it can be null, in which case the listener receives a List<Foo> where Foo is the unconverted ConsumerRecord.value() (List<String> with default Boot configuration); with a converter it gets List<Bar> where the Bars are converted from ConsumerRecord.value().

That said, I think a better solution would be to auto-configure a BatchMessageConverter (alongside the RecordMessageConverter) for use with batch listeners.

That would give the user more control over the converter, rather than hard-wiring a BatchMessagingMessageConverter implementation that wraps the configured RecordMessageConverter.

[leochans]

@garyrussell I had think about RecordMessageConverter be null thing, when it is null, BatchMessageConverter will not do the convert, see BatchMessagingMessageConverter:163

it's already init a BatchMessageConverter in BatchMessagingMessageListenerAdapter use a new BatchMessagingMessageConverter(), in the BatchMessagingMessageConverter() called this(null)

[garyrussell]

I understand that (I wrote the code); it can be null without problems, but test cases are needed to ensure the configuration works as expected.

However, I think my suggestion to auto-configure a BatchMessageConverter is a better solution (but it could fall back to your code if none is provided, but a RecordConverter is).

[snicoll]

Thank you for the PR @leochans but I've decided to take a different approach based on the feedback from @garyrussell, see #15942 for more details.