Using published events

Thoth provides helpers to deserialize published events correctly.

Event format

Published events aren’t raw BankEvent, they are wrapped in an “Envelope” that contains the event and some meta-data.

Envelope class has the following fields:

  • id: unique ID of the event (UUID)
  • sequenceNum: incremental sequenceNum (sequence is common to all events)
  • eventType: type of the event (MoneyWithdrawn, AccountOpened, …)
  • emissionDate: date of event emission
  • metadata: JSON field that could contain additional metadata about the event
  • event: event serialized as JSON
  • context: JSON field that could contain additional context information about the event
  • version: version of the event
  • published: field used internally by thoth to indicate event publication, consumer shouldn’t use it
  • transactionId: id of the database transaction that created the event. It can be used to aggregate and consume at once every event of a given transaction (to ensure data consistency for instance).
  • totalMessageInTransaction: number total of messages created during the database transaction, useful to aggregate and consume at once events of a transaction.
  • numMessageInTransaction: indicate position of this event among other events created during the database transaction, useful to consume in the correct order all events created during a transaction.
  • entityId: id of the business entity concerned by this event
  • userId: id of the user that triggered event creation, useful for audit purposes
  • systemId: id of the system that triggered event creation, useful for audit purposes

Consume events

Thoth provides an helper to deserialize event value.

Map<String, Object> props = new HashMap<>();

props.put(
    ConsumerConfig.BOOTSTRAP_SERVERS_CONFIG,
    bootstrapAddress);
props.put(
    ConsumerConfig.GROUP_ID_CONFIG,
    groupId);

KafkaConsumer<String, EventEnvelope<BankEvent, Tuple0, Tuple0>> consumer = new KafkaConsumer<>(
        props,
        new StringDeserializer(),
        JsonDeserializer.of(new BankEventFormat())
);
The source code for this page can be found here.