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.
We now allow externalizing application events to a variety of message brokers through the addition of Spring Modulith modules for Kafka, AMQP and JMS to a user project's classpath. Which events shall be externalized and how they're supposed to be routed to the message broker can be configured through either annotations or via a configuration API declared as Spring bean.
In case Jackson is on the classpath, we also add auto-configuration to use a Boot-configured ObjectMapper instance with the corresponding message broker client APIs to properly serialize and deserialize messages to JSON.
