entityManager.getTransaction().begin();
java.sql.Connection connection = entityManager.unwrap(java.sql.Connection.class); // unwraps the Connection class.
...
entityManager.getTransaction().commit();

entityManager.getTransaction().begin();
UnitOfWork unitOfWork = (UnitOfWork)((JpaEntityManager)entityManager.getDelegate()).getActiveSession();
unitOfWork.beginEarlyTransaction();
Accessor accessor = unitOfWork.getAccessor();
accessor.incrementCallCount(unitOfWork.getParent());
accessor.decrementCallCount();
java.sql.Connection connection = accessor.getConnection();
...
entityManager.getTransaction().commit();

Session hibernateSession = entityManager.unwrap(Session.class);
Connection jdbcConnection = hibernateSession.connection();

Connection connection = entityManager().unwrap(SessionImpl.class).connection();

private void executeNative(final String query) {
    Session session = entityManager.unwrap(Session.class);
    session.doWork(new Work() {

        @Override
        public void execute(Connection connection) throws SQLException {
            Statement s = null;
            try {
                s = connection.createStatement();
                s.executeUpdate(query);
            }
            finally {
                if (s != null) {
                    s.close();
                }
            }
        }

    });
}

SessionImpl sessionImpl = (SessionImpl) session;
Connection conn = sessionImpl.connection();

import java.sql.Connection;
import org.apache.openjpa.persistence.OpenJPAEntityManager;
import org.apache.openjpa.persistence.OpenJPAPersistence;



public final class MsSqlDaoFactory {


   public static final Connection getConnection(final EntityManager entityManager) {
          OpenJPAEntityManager openJPAEntityManager = OpenJPAPersistence.cast(entityManager);
          Connection connection = (Connection) openJPAEntityManager.getConnection();
          return connection;

    }

}

Statement statement = null;
EntityManager em = null;
em = emf.createEntityManager();
EntityTransaction et = em.getTransaction();

if(!et.isActive()) {
    et.begin();
}

java.sql.Connection connection = em.unwrap(java.sql.Connection.class);

    String qquerry="SELE ...
    try {
        statement = connection.createStatement();
        ResultSet rs =  statement.executeQuery(qquerry);

        if (!rs.next()) {
            return null;
        }
        else{
            wwwwas=rs.getString(4);
        }
        statement.close();
        }
    catch (SQLException e) {
        System.out.println("n b-03:"+e);
        throw new RuntimeException(e.getMessage(), e);
    }
    finally {
        try {
            //  em.getTransaction().commit();
            if(connection != null )
            connection.close();
        }
        catch (Exception e) {
            throw new RuntimeException(e.getMessage(), e);
       }
    }