Getting and using a Connection from an EntityManager.

EclipseLink

As described in Getting a JDBC Connection from an EntityManager, we can unwrap an EntityManager into a Connection.

final EntityManagerFactory factory = entityManagerFactory();
final EntityManager manager = factory.createEntityManager();
manager.getTransaction().begin();
try {
    final Connection connection = manager.unwrap(Connection.class);
} catch (final PersistenceException pe) {
    logger.error("failed to unwrap EntityManager into a Connection", pe);
}
manager.getTransaction().commit();
manager.close();
factory.close();

Hibernate

Let’s follow this excellent answer using reflections.

final EntityManagerFactory factory = entityManagerFactory();
final EntityManager manager = factory.createEntityManager();
//manager.getTransaction().begin();
final Class<?> sessionClass;
try {
    sessionClass = Class.forName("org.hibernate.Session");
} catch (final ClassNotFoundException cnfe) {
    //logger.debug("class not found", cnfe);
    return;
}
final Object session = manager.unwrap(sessionClass);
final Class<?> workClass;
try {
    workClass = Class.forName("org.hibernate.jdbc.Work");
} catch (final ClassNotFoundException cnfe) {
    //logger.debug("class not found", cnfe);
    return;
}
final Method executeMethod;
try {
    executeMethod
        = workClass.getMethod("work", Connection.class);
} catch (final NoSuchMethodException nsme) {
    return;
}
final Object workProxy = Proxy.newProxyInstance(
        workClass.getClassLoader(),
        new Class[]{workClass},
        (proxy, method, args) -> {
            if (method.equals(executeMethod)) {
                final Connection connection = (Connection) args[0];
                result.add(function.apply(connection));
            }
            return null;
        }
);
sessionClass.getMethod("doWork", workClass).invoke(session, workProxy);
//manager.getTransaction().commit();
manager.close();
factory.close();