At first let's have a look at the contents of a vertically sliced module. Since it is modeled after business concerns, the module will include everything necessary to fulfill certain functionality.

First of all, the module includes technical entry points for use cases such as HTTP endpoints, presentation framework controllers, or JMS endpoints. These classes and methods usually make use of Java EE principles, such as inversion of control, to be called from the container as soon as some communication hits the application.

The functionalities that initiate the actual use cases are the next and equally important concern. They usually differ from the technical endpoints such that they don't contain any communication logic. The business use case boundaries are the entry point of our domain logic. They are implemented as managed beans, usually Stateless Sessions Beans, EJBs in other words, or CDI managed beans.

The boundaries initiate and implement the business logic. In cases where the logic of a use case consists of just a few steps the boundary can sufficiently contain the whole logic in the business method or private methods in the class definition. Then no other delegate is required. For the vast majority of use cases the boundary would delegate logic to corresponding services. These delegates have finer-grained responsibilities. Depending on the domain this includes implementing detailed business logic or accessing external systems such as databases. Following Domain-Driven Design language, these classes include services, transaction scripts, factories, and repositories.

The next type of objects are all classes that typically would be considered as model content, such as entities, value objects, and transfer objects. These classes represent the entities in the domain, but also can, and should, implement business logic. Examples are entity beans that are managed in the database, other POJOs, and enumerations.

In some cases the package might also contain cross-cutting concerns such as interceptors with business or technical responsibilities. All these types of components now have to be organized within a module.