Transactional Event Library for Jakarta EE 8

A Transactional Event Library that implements the outbox pattern for Jakarta EE 8.

Used Jakarta EE APIs

The following APIs are required:

• CDI 2.0
• Concurrency Utilities 1.0
• JDBC 4.2
• JTA 1.2

The following APIs are optionally supported for serialization:

• JAXB 2.2
• JSON-B 1.0

Publish an Event

An Event can be published using the EventPublisher API:

   @Inject
   private EventPublisher publisher;
   
   public void someMethod() {
      ...
      SomeEvent event = ...
      publisher.publish(event);
      ...
   }

Handle an Event

For every event type published there must be a corresponding Handler (qualified by EventHandler):

@Dependent
@EventHandler
class SomeEventHandler extends AbstractHandler<SomeEvent> {
   @Override
   protected void handle(SomeEvent event) {
      ...
   }
}

Data Source

The library expects that the following table exists when using the javax.sql.DataSource with the Events qualifier:

CREATE TABLE event_store (
	id VARCHAR(50) NOT NULL,
	event_type VARCHAR(50) NOT NULL,
	payload VARCHAR(4000) NOT NULL,
	published_at TIMESTAMP NOT NULL,
	tries INT NOT NULL,
	lock_owner VARCHAR(50),
	locked_until BIGINT NOT NULL,
	PRIMARY KEY (id)
);

CREATE INDEX event_store_locked_until ON event_store (locked_until);

The required javax.sql.DataSource can be specified like the following:

@Dependent
class EventsDataSource {
   @Events
   @Produces
   @Resource(name = "someDb")
   private DataSource dataSource;
}

Metrics (if mpMetrics is available)

If mpMetrics is enabled on the server there will be the following metrics

• application_com_github_jonasrutishauser_transaction_event_published_total (number of published events)
• application_com_github_jonasrutishauser_transaction_event_failedattempts_total (these are the number of failed attempts to process an event)
• application_com_github_jonasrutishauser_transaction_event_success_total (these are the number of successfully processed events)
• application_com_github_jonasrutishauser_transaction_event_blocked_total (these are the number of blocked events because the maximum number of retries has been reached)
• application_com_github_jonasrutishauser_transaction_event_unblocked_total (these are the number of unblocked events)
• application_com_github_jonasrutishauser_transaction_event_deleted_total (these are the number of deleted events)
• application_com_github_jonasrutishauser_transaction_event_processing (the number of events being processed currently in total)
• application_com_github_jonasrutishauser_transaction_event_dispatched_processing (the number of dispatched events by a timer being processed currently. This metric can be used for fine-tuning transactional.event.maxConcurrentDispatching and transactional.event.maxAquire)
• application_com_github_jonasrutishauser_transaction_event_all_in_use_interval (interval between lookups for events to process when maxConcurrentDispatching is reached)
• application_com_github_jonasrutishauser_transaction_event_max_dispatch_interval (maximum interval between lookups for events to process)
• application_com_github_jonasrutishauser_transaction_event_initial_dispatch_interval (initial interval between lookups for events to process)
• application_com_github_jonasrutishauser_transaction_event_max_aquire (maximum number of events aquired per query)
• application_com_github_jonasrutishauser_transaction_event_max_concurrent_dispatching (maximum number of dispatched events being processed concurrently)
• application_com_github_jonasrutishauser_transaction_event_dispatch_interval (interval between lookups for events to process)