JPA.java

package jpa;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.EntityTransaction;
import javax.persistence.Persistence;

public class JPA {

    EntityManagerFactory emf;

    public static void main(String[] args) {
        new JPA();
    }

    public JPA() {

        emf = Persistence.createEntityManagerFactory("JPATestPU");
        try {
            Person person = new Person();
            person.setName("Tina");

            createEntity(person);
            Object id = person.getId();

            System.out.println("" + readEntity(Person.class, id));

        } finally {
            emf.close();
        }
    }

    //It works as well with the definiton
    //"void createEntity(Object entity)"
    public final <T> void createEntity(T entity) {
        EntityManager em = emf.createEntityManager();
        EntityTransaction tx = em.getTransaction();
        try {
            tx.begin();
            em.persist(entity);
            tx.commit();
        } catch (RuntimeException ex) {
            if (tx != null && tx.isActive()) {
                tx.rollback();
            }
            throw ex;
        } finally {
            em.close();
        }
    }

    public final <T> T readEntity(Class<T> clss, Object id) {
        EntityManager em = emf.createEntityManager();
        try {
            return em.find(clss, id);
        } finally {
            em.close();
        }
    }
}