Refactor EmailService

[Flashky]

Currently EmailService receives a PacktFreeOffer, so it is tightly coupled to that domain object.

The following is proposed to loose the coupling:

• Create a specific email model class EmailData.
• Create a specific EmailService interface with method:
  • void send(EmailData)
• Modify EmailService:
  • Rename it to SimpleJavaMailService.
  • Remove NotificationListener interface and add EmailService interface instead.
  • Adapt the current notify(PacktFreeOffer) method to send(EmailData) method.
• Create an adapter class EmailNotifier which will implement NotificationListener interface. This class will send the object to the wrapped inside the EmailData class to the SimpleJavaMailService .
• Modify NotifierPacktApplication class to initialize the new EmailListener there instead of the old one.

This task should be priotirized first, as the old task should continue working as before, and then we can do the following tasks.

[Flashky]

Done.