Enterprise JavaBeans - Example

Example

The following shows a basic example of what an EJB looks like in code:

@Stateless public class CustomerService { @PersistenceContext private EntityManager entityManager; public void addCustomer(Customer customer) { entityManager.persist(customer); } }

The above defines a service class for persisting a Customer object (via O/R mapping). The EJB takes care of managing the persistence context and the addCustomer method is transactional and thread-safe by default. As demonstrated, the EJB focuses only on business logic and persistence and knows nothing about any particular presentation.

Such an EJB can be used by a class in e.g. the web layer as follows:

@Named @RequestScoped public class CustomerBacking { @EJB private CustomerService customerService; public String addCustomer { customerService.addCustomer(customer); context.addMessage(...); // abbreviated for brevity return "customer_overview"; } }

The above defines a JavaServer Faces (JSF) backing bean in which the EJB is injected by means of the @EJB annotation. Its addCustomer method is typically bound to some UI component, like a button. Contrary to the EJB, the backing bean does not contain any business logic or persistence code, but delegates such concerns to the EJB. The backing bean does know about a particular presentation, of which the EJB had no knowledge.