This example illustrates event sourcing with Akka Persistence.

it is based (okay, stolen from) the generated sample project akka-samples-peristence-java but with some Kotlin grammar and idiom applied. This project is open for improvement, so if you find some code that could be more Kotlin-like or better in any way, then don't hesitate to prepare a PR.

Study the source code of ShoppingCart.kt. 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
• onPersistFailure defines restarts with backoff in case of failures

Tests are defined in ShoppingCartTests.kt. To run the tests, enter:

gradle test

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