Now we have seen how the GoF design patterns are implemented in the age of Java EE. Besides that, I want to point out some patterns and concepts that are applied in our core domain before continuing to more purely technical concerns. The book Domain-Driven Design by Eric Evans, extensively describes these patterns and concepts that support constructing software models that match the actual business domain as accurately as possible. In particular, the importance of communicating with domain experts, sharing a common, ubiquitous domain language, deeply understanding the underlying domain model, and gradually refactoring it, is pointed out. Domain-Driven Design also introduces certain concepts in the software world, such as repositories, services, factories, or aggregates.

Now the question arises as to whether and how these concepts are realizable with Java Enterprise? Domain-Driven Design always aims to include important aspects of the application directly into the domain model rather than just outside as part of a service or transaction script. We will see how this fact plays well with EJBs or CDI managed beans.