Creating an JPA EntityManager

EntityManager-sample.java

// in JavaSE environment 
EntityManagerFactory emf = Persistence.createEntityManagerFactory("sample");
EntityManager em = emf.createEntityManager();

try{
   ...

]
finally{
   em.close();
   emf.close();

}

// in JavaEE environment
// the name is optional when your persistence.xml descriptor has only one PU
@PersistenceContext(unitName="sample")
EntityManager em;

// when you wish, for some particular reason, create your own EntityManager in a JavaEE env, inject the EMF
@PersistenceUnit(unitName="sample")
EntityManagerFactory emf;