Question

I am making a Java EE application just to use what I learn while reading in the books. I made a simple Entity and a DAO object that do different actions on this Entity such as create, update etc. Then in my EJB I want to use this DAO object so that I later can expose it to JSF etc.

I am having a little problems of understanding how to use objects of different classes in different layers of my application. How do I expose them to each other?

Do I just do as in regular Java SE? Have properties for the different classes and instantiate them in the classes I want? (No probably not, I have seen the use of @Inject and so on, but I do not understand one bit of it. And not when I can use it either)

I would apprciate some text on when/how we use the different annotations and how we connect different layers rather than just some code showing it.

I am on the Java chat if anyone have some spare time =)

Answer 1

You’re asking too general questions. Grab some decent book on Java EE (there are tons of them). For better understanding of dependency injection, I’d recommend official Weld documentation. However here is a typical example aimed to show you how to connect different Java EE layers:

JPA Entity:

@Entity
public class Employee {

  @Id
  private Long id;

  private String name;

  //getters and setters
}

EJB bean:

@Stateless
public class EmployeeService {

  //The entity manager will be injected automatically  
  @PersistenceContext
  private EntityManager em;

  public Employee findEmployeeById(Long id) {
    return em.find(Employee.class, id);
  }

}

JSF controller (let’s assume it’s CDI-bean):

@Named
@SessionScoped
public class EmployeeController implements Serializable {

  //using CDI @Inject annotation empService will be initialized automatically
  @Inject
  private EmployeeService empService;

  //this method can be called from .xhtml page
  public String obtainEmployeeName(Long id) {
    String empName = "";
    Employee emp = empService.findEmployeeById(id);
    if (emp != null) {
      empName = emp.getName();
    }
    return empName;
  }
}

xhtml page:

<h:outputText value="#{employeeController.obtainEmployeeName(3)}" />

Update
Some books that might help: