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Publishing messages

A producer builds an Avro message with its generated builder and sends it through a KafkaTemplate<AvroMessageKey, AvroMessage>. For the default cluster, inject the KafkaTemplate directly; for a non-default cluster add @Qualifier("<clusterName>") on the injected template (see Configuration reference).

A publisher component​

@Component
@RequiredArgsConstructor
class DeclarationPublisher {
    private final KafkaTemplate<AvroMessageKey, AvroMessage> kafkaTemplate;

    void publish(String declarationId) {
        JmeDeclarationCreatedEvent event = JmeDeclarationCreatedEventBuilder.create()
                .idempotenceId(declarationId)
                .declarationIdReference(declarationId)
                .build();
        kafkaTemplate.send("jme-messaging-declaration-created", event);
    }
}

Each message type ships with a generated builder (e.g. JmeDeclarationCreatedEventBuilder). These builders extend a jEAP base class — AvroDomainEventBuilder for events and AvroCommandBuilder for commands (from jeap-messaging-avro) — which auto-fills the MessageType information (type name, version, identity, timestamps; see Defining messages). Always build messages through these builders rather than constructing the Avro objects by hand, and set a meaningful idempotenceId, as consumers rely on it to deduplicate.

kafkaTemplate.send(topic, message) returns a future. To send synchronously, block on it with .get(timeout).

Choosing the topic​

A message type has a default topic taken from its registry descriptor; you can also send to an explicit topic name as shown above.

The MessagePublisher abstraction​

jeap-messaging-api defines a MessagePublisher interface. Implement a publisher class that decides where messages go, and inject it into your message generators. This is a system-layer concept that keeps the routing decision out of the business code — see Architecture.

Producer contract required​

A producer contract is REQUIRED for every produced type (see Message contracts). The publishWithoutContractAllowed property must be false in production (see Configuration reference).

Multi-cluster caveat with Lombok​

When using a @Qualifier("<clusterName>") on a constructor-injected KafkaTemplate, note that Lombok does NOT copy field annotations to generated constructors by default. Configure lombok.copyableAnnotations so the qualifier reaches the generated constructor, otherwise the wrong cluster's template may be injected. See https://projectlombok.org/features/constructor.