Plain Java together with CDI and EJB form the core domain components of a modern Java EE application. Why is it called core domain? As mentioned, we want to pay attention to the actual business. There are aspects, components, and functionality that serve the business purpose at their core, whereas others just support, make the business domain accessible, or fulfill other technical requirements.

Java EE ships with many APIs that support realizing dozens of technical requirements. Most of them are technically motivated though. The biggest advantage of the Java EE platform, however, is that clean Java business logic can be implemented with minimal code impact of the technology. The APIs required for that are mainly CDI and EJB. Other APIs, that are required for technical motivations, such as JPA, JAX-RS, JSON-P, and many others, are introduced with a secondary priority.

Managed beans, no matter whether CDI or EJB, are implemented as annotated Java classes, without any technical super classes or interfaces required. In the past, this was called the no-interface view. Nowadays this is the default case. Extending classes obscure the picture on the domain and also come with other shortcomings when it comes to testability. A modern framework integrates itself as simply and as lean as possible.