Understanding HelloService implementation code

In this section, we will try to understand the Hello Service implementation (hello-lagom-impl) code. This is an implementation microservice for the Hello Reactive System.

It has the HellolagomState state, as shown here:

case class HellolagomState(message: String, timestamp: String) 
 
object HellolagomState { 
  implicit val format: Format[HellolagomState] = 
   Json.format[HellolagomState] 
}

It has the HellolagomEvent event, as show here:

sealed trait HellolagomEvent extends AggregateEvent[HellolagomEvent] { 
  def aggregateTag = HellolagomEvent.Tag 
} 
 
object HellolagomEvent { 
  val Tag = AggregateEventTag[HellolagomEvent] 
} 

We have defined the following GreetingMessageChanged event to represent the change in the GreetingMessage state:

case class GreetingMessageChanged(message: String) extends HellolagomEvent 
 
object GreetingMessageChanged { 
  implicit val format: Format[GreetingMessageChanged] = 
                                      ...