This example illustrates event sourcing with Apache Pekko Persistence.

Study the source code of the ShoppingCart.scala. A few things to note:

• The actor is implemented with the EventSourcedBehavior
• It defines Command, Event and State
• Commands define replyTo: ActorRef to send a confirmation when the event has been successfully persisted
• State is only updated in the event handler
• withRetention to enable snapshotting
• onPersistFailure defines restarts with backoff in case of failures

Tests are defined in ShoppingCartTest.java. To run the tests, enter:

mvn test

The ShoppingCart application is expanded further in the pekko-sample-cqrs-java sample. In that sample the events are tagged to be consumed by even processors to build other representations from the events, or publish the events to other services.