Mastering Spring 5.0

Approach 1 - sequential approach

Let's consider three services--CustomerInformationService, MailService, and EmailService, which can provide the capabilities listed earlier. We can create NewCustomerService with the following steps:

1. Call CustomerInformationService to save customer information to the database.
2. Call MailService to mail the welcome kit.
3. Call EmailService to send the e-mail notification.

NewCustomerService becomes the central place for all business logic. Imagine if we have to do more things when a new customer is created. All that logic would start accumulating and bloating up NewCustomerService.