Fare query scrittura e lettura con PersistenceManager

PersistenceManager.initialize();
        
try {
    EntityManager entityManager = PersistenceManager.getEntityManagerFactory().createEntityManager();
    entityManager.getTransaction().begin();

    User user = new User();
    user.setUsername("mariorossi01");
    entityManager.persist(user);

    List<User> users = entityManager.createQuery("SELECT u FROM User u", User.class).getResultList();
    for (User u : users) {
        System.out.println("User: " + u.getId() + ", " + u.getUsername());
    }

    entityManager.getTransaction().commit();
}catch(Exception e){
    return;
}

PersistenceManager.close();