Java Persistence API

Using Entities in Java EE Applications

EntityManagers are obtained via "Dependency Injection"
Within the context of an EJB method, the JTA transaction will be started for you

EJB Example

  @Stateless
  public class EmployeeDaoImpl implements EmployeeDao {
    @PersistenceContext
    private EntityManager entityManager;

    public Collection getAllEmployees() {
      Query query = entityManager.createQuery( "select x from Employee x" );
      return query.getResultList();
    }
    ...
  }

In a servlet environment, you must initiate the JTA transactions yourself (a servlet filter maybe)

Servlet Example