// Read customer from database
EntityManagerFactory emf = 
    Persistence.createEntityManagerFactory("CustomerService");
EntityManager em = emf.createEntityManager();
Customer customer = em.find(Customer.class, (long) 1);
         
// Save customer to XML
JAXBContext jc = JAXBContext.newInstance(Customer.class);
Marshaller marshaller = jc.createMarshaller();
StringWriter writer = new StringWriter();
marshaller.marshal(customer, writer);
        
// Load customer from XML 
Unmarshaller unmarshaller = jc.createUnmarshaller();
StringReader reader = new StringReader(writer.toString());
Customer detachedCustomer = 
    (Customer) unmarshaller.unmarshal(reader);
detachedCustomer.setLastName("Jones");
 
// Persist customer to database
Customer mergedCustomer = em.merge(detachedCustomer);
em.getTransaction().begin();
em.persist(mergedCustomer);
em.getTransaction().commit();
em.close();