Federico Mariani created CAMEL-24797:
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Summary: camel-core - Splitter should unwrap Exchange parts like
Message parts (List<Exchange> from batching consumers)
Key: CAMEL-24797
URL: https://issues.apache.org/jira/browse/CAMEL-24797
Project: Camel
Issue Type: Improvement
Components: camel-kafka, camel-core
Reporter: Federico Mariani
Splitting a body of type {{List<Exchange>}} (the shape produced by the
camel-kafka batching consumer, {{batching=true}}, and by
{{GroupedExchangeAggregationStrategy}}) creates child exchanges whose *body is
the {{Exchange}} object itself* and whose *headers are empty*. Only {{Message}}
parts are unwrapped by the Splitter today (the branch added for CAMEL-9252).
Verified on 4.22.0 with a plain {{from("direct:a").split(body())}} route:
||Body shape||Child {{${body}}}||Child headers||
|{{List<Exchange>}}|{{Exchange[]}}|none|
|{{List<Message>}}|the record body|preserved|
So {{.split(body()).to("kafka:out")}} after a batching consumer silently
publishes {{Exchange[]}} as record value, and any filter/transform on the
record headers sees nothing.
*Why this matters now*: the Kafka batching docs added in 4.22 (CAMEL-20428, PR
#25006, "Batch Headers" section) explicitly recommend {{.split(body())}} on the
batch exchange, and work around the header loss by storing the topic in a
variable before the split. The batching consumer proposed for camel-sjms (dev
list thread, CAMEL-16039 / CAMEL-20368) will copy the same {{List<Exchange>}}
shape, so the gap gets copied with it.
CAMEL-9323 asked for this in 2015 and was closed as Won't Fix, pointing to
{{List<Message>}} as the supported shape. That predates a core component
producing {{List<Exchange>}} itself and documenting a split over it.
*Proposed outcomes* (one of):
# Splitter unwraps {{Exchange}} parts like it does {{Message}} parts: set the
child's message from {{part.getMessage()}} (a few lines next to the existing
{{instanceof Message}} branch in {{Splitter}}), plus an upgrade-guide note
since {{getBody()}} on the child changes for that case.
# Or: keep the Splitter as is, and change the Kafka batching docs to stop
recommending {{split}} and show reading each child with
{{getBody(Exchange.class)}} instead; future batching consumers document the
same.
_Claude Code on behalf of Federico Mariani_
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