Events: Transactional Observers

[hendryluk]

Expanding on #7

CDI spec allows you to specify that a particular observer should receive event notifications during the before or after completion phase of the transaction in which the event was raised. I.e. it defers the notifications of an event until the intended phase of the transaction has been reached (as opposed to the current implementation that only allows immediate notifications).
Ref: https://docs.jboss.org/weld/reference/latest/en-US/html/events.html#_transactional_observers

Supported options are:

• IN_PROGRESS
• AFTER_SUCCESS
• AFTER_FAILURE
• AFTER_COMPLETION
• BEFORE_COMPLETION

Example

public void OnLoggedIn([Observes(During=TransactionPhase.AfterSuccess)] LoggedIn evt)
{
   /* handles */
}

This is important e.g. in scenario where you want to send an outbound customer email only after the transaction has been successfully committed.