EventExternalizationConfiguration now exposes a ….headers(Class<T>, Function<T, Map<String, Object>) to allow to define a function that extracts headers from the event that are supposed to added to the message to be sent out. The Kafka and AMQP implementations have been augmented to consider those configurations.
Furthermore, if the mapping step prior to the externalization creates a Spring Message<?>, we add routing information as fallback and send it out as is.
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