Reconnect JPA (Hibernate) EntityManager to JDBC connection

package org.hibernate.jpa.internal;

import org.hibernate.Session;
import org.hibernate.SessionFactory;
import org.hibernate.internal.SessionImpl;

import javax.annotation.Nonnull;
import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import java.sql.Connection;
import java.sql.SQLException;

/**
 * Manipulates Hibernate internals to allow connecting an {@link EntityManager}
 * to a new JDBC connection when the old connection of the EntityManager has died.
 *
 * @see <a href="http://stackoverflow.com/questions/24060782/jpa-2-hibernate-persistence-context-per-conversation-closed-connection">JPA 2 (Hibernate) persistence context per conversation - closed connection</a>
 *
 */
public class EntityManagerFactoryAdapter {

    private final EntityManagerFactoryImpl entityManagerFactory;

    public EntityManagerFactoryAdapter(EntityManagerFactory entityManagerFactory) {
        this.entityManagerFactory = (EntityManagerFactoryImpl)entityManagerFactory;
    }

    /**
     * Reconnects given {@code entityManager} to the given {@code connection}
     * if the database connection of the EntityManager has been closed.
     * Does nothing if the EntityManager already has an open connection.
     *
     * @param entityManager The EntityManager to reconnect
     * @param connection The connection to connect the EntityManager to
     */
    public void reconnect(@Nonnull EntityManager entityManager, @Nonnull Connection connection) {
        SessionImpl existingSession = entityManager.unwrap(SessionImpl.class);

        try {
            if (existingSession.connection().isClosed()) {
                existingSession.disconnect();
                existingSession.reconnect(connection);
            }
        } catch (SQLException e) {
            throw new RuntimeException("Failed reconnecting EntityManager to given JDBC connection.", e);
        }
    }

    /**
     * Creates a new EntityManager that uses the given JDBC connection
     * for database access.
     *
     * @param connection The JDBC connection to use in the EntityManager
     * @return The created EntityManager
     */
    @Nonnull
    public EntityManager createEntityManager(@Nonnull Connection connection) {
        // Create new EntityManager & close the session attached to it.
        // Otherwise the original session is left open.
        EntityManagerImpl entityManager = (EntityManagerImpl)entityManagerFactory.createEntityManager();
        entityManager.unwrap(Session.class).close();

        // Replace EntityManager session with session created with
        // specified JDBC connection. Necessary to be able to
        // later call .reconnect(connection) on the session.
        SessionFactory sessionFactory = entityManagerFactory.getSessionFactory();
        entityManager.session = sessionFactory.withOptions()
                                              .connection(connection)
                                              .openSession();

        entityManager.getTransaction().begin();

        return entityManager;
    }
}