CAMEL-23584: camel-kafka - align Exchange header constant names with Camel naming convention

[oscerd]

Summary

Renames the Exchange header string values in KafkaConstants from the non-Camel-prefixed kafka.* namespace to the project-wide CamelKafka* PascalCase convention, completing the camel-kafka sub-task under the CAMEL-23577 umbrella header-naming-convention sweep.

Rename table

Constant	Previous value	New value
KafkaConstants.PARTITION_KEY	kafka.PARTITION_KEY	CamelKafkaPartitionKey
KafkaConstants.PARTITION	kafka.PARTITION	CamelKafkaPartition
KafkaConstants.KEY	kafka.KEY	CamelKafkaKey
KafkaConstants.TOPIC	kafka.TOPIC	CamelKafkaTopic
KafkaConstants.OVERRIDE_TOPIC	kafka.OVERRIDE_TOPIC	CamelKafkaOverrideTopic
KafkaConstants.OFFSET	kafka.OFFSET	CamelKafkaOffset
KafkaConstants.HEADERS	kafka.HEADERS	CamelKafkaHeaders
KafkaConstants.LAST_RECORD_BEFORE_COMMIT	kafka.LAST_RECORD_BEFORE_COMMIT	CamelKafkaLastRecordBeforeCommit
KafkaConstants.LAST_POLL_RECORD	kafka.LAST_POLL_RECORD	CamelKafkaLastPollRecord
KafkaConstants.TIMESTAMP	kafka.TIMESTAMP	CamelKafkaTimestamp
KafkaConstants.OVERRIDE_TIMESTAMP	kafka.OVERRIDE_TIMESTAMP	CamelKafkaOverrideTimestamp
KafkaConstants.KAFKA_RECORD_META	kafka.RECORD_META	CamelKafkaRecordMeta

KafkaConstants.MANUAL_COMMIT was already Camel-prefixed (CamelKafkaManualCommit) and is unchanged. The non-header constants in the class (KAFKA_DEFAULT_ENCODER, KAFKA_STRING_ENCODER, KAFKA_DEFAULT_SERIALIZER, KAFKA_DEFAULT_DESERIALIZER, PARTITIONER_RANGE_ASSIGNOR, KAFKA_SUBSCRIBE_ADAPTER) are not Exchange headers and are unchanged.

Backwards-compatibility

• Java field names are unchanged. Routes that reference the constants symbolically (setHeader(KafkaConstants.OVERRIDE_TOPIC, ...)) continue to work without changes.
• Routes hard-coding the literal kafka.* strings (e.g. setHeader("kafka.OVERRIDE_TOPIC", ...) or Simple expressions like ${headers[kafka.TOPIC]}) must be updated to the new CamelKafka* values.
• The 4.21 upgrade guide entry is marked as a "potential breaking change" with the full rename table and a worked example, given the wider installed base of camel-kafka than the niche sibling components in the sweep.
• The Endpoint DSL header accessor method names on KafkaEndpointBuilderFactory$KafkaHeaderNameBuilder (e.g. kafkaOverrideTopic(), kafkaTopic(), kafkaPartitionKey()) keep their method names; only the returned string value reflects the new convention.

Cross-module updates

• KafkaHeaderDeserializer and the bundled Kafka Connect-style transformers (RegexRouter, TimestampRouter, MessageTimestampRouter, ValueToKey) now use the symbolic KafkaConstants references instead of literal "kafka.*" strings.
• The local copies of the constants in org.apache.camel.tracing.decorators.KafkaSpanDecorator (deprecated since 4.19.0) and org.apache.camel.telemetry.decorators.KafkaSpanDecorator are kept in sync with the new values so Kafka span tagging continues to work for routes that have migrated to the new header names.
• The camel-opentelemetry2 mock Kafka producer and SpanKindTest are updated to use the new header names.
• KafkaProducerTest, RegexRouterTest, and KafkaConsumerFullIT are updated to use the KafkaConstants symbolic references.
• The consumer examples in kafka-component.adoc that use Simple expressions to read these headers (${headers[CamelKafkaTopic]} etc.) are updated.

Regenerated artifacts

• components/camel-kafka component catalog (kafka.json)
• Project-wide catalog/camel-catalog mirror and important-headers.json
• core/camel-util/ImportantHeaderUtils.java
• dsl/camel-endpointdsl/.../KafkaEndpointBuilderFactory.java

Plus the new camel-kafka - potential breaking change entry in docs/user-manual/modules/ROOT/pages/camel-4x-upgrade-guide-4_21.adoc.

Sibling sub-tasks under CAMEL-23577

This sub-task follows the pattern established in CAMEL-23576 (camel-jira), CAMEL-23574 (camel-dns), CAMEL-23575 (camel-mongodb-gridfs), CAMEL-23578 (camel-web3j), CAMEL-23579 (camel-pdf), CAMEL-23580 (camel-openstack), CAMEL-23581 (camel-elasticsearch / camel-opensearch), CAMEL-23582 (camel-github2), CAMEL-23585 (camel-arangodb), CAMEL-23587 (camel-jt400), CAMEL-23588 (camel-undertow), CAMEL-23590 (camel-milo), CAMEL-23592 (camel-shiro), CAMEL-23597 (camel-solr), and CAMEL-23629 (camel-irc).

Test plan

• mvn install in components/camel-kafka — passes (unit tests + catalog regen)
• mvn test in components/camel-tracing — passes
• mvn test in components/camel-telemetry — passes
• mvn test in components/camel-opentelemetry2 — passes (after mvn install of upstream changes — SpanKindTest correctly exercises the renamed headers through the camel-telemetry KafkaSpanDecorator)
• Full reactor mvn clean install -DskipTests from root — passes, all downstream catalog / DSL / important-headers generators regenerate cleanly

Reported by Claude Code on behalf of Andrea Cosentino

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🧪 CI tested the following changed modules:

• catalog/camel-catalog
• components/camel-kafka
• components/camel-opentelemetry2
• components/camel-telemetry
• components/camel-tracing
• core/camel-util
• docs
• dsl/camel-endpointdsl

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Build reactor — dependencies compiled but only changed modules were tested (8 modules)

• Camel :: Catalog :: Camel Catalog
• Camel :: Common Telemetry
• Camel :: Common Tracing (deprecated)
• Camel :: Docs
• Camel :: Endpoint DSL
• Camel :: Kafka
• Camel :: Opentelemetry 2
• Camel :: Util

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[gnodet]

Standard header rename for camel-kafka: kafka.PARTITION_KEY → CamelKafkaPartitionKey, kafka.KEY → CamelKafkaKey, etc. Follows the established Camel header naming convention. The bulk of the diff is generated catalog metadata, which is consistent with the constant renames.

Upgrade guide entry and documentation updates included.

LGTM.

Fully automatic review from Claude Code