Use Hibernate 4.3.x with JTA on Glassfish 4

This will allow you to upgrade to JPA 2.1 using the new Hibernate framework on Java EE 7 and maintain your JTA datasources with a standard JPA EntityManager.

First you will want to download Hibernate 4.3.x from http://hibernate.org/orm/downloads/ and drop all the required jars in the zip in {Glassfish4 direcory}/glassfish/lib
I also installed jboss-logging-3.1.x.GA.jar in the {Glassfish4 direcory}/glassfish/lib/endorsed folder to allow Hibernate logging.

I recommend using Maven for your project dependency management since Hibernate has a large dependency tree. Add the following dependency to pom.xml

<dependency>
    <groupId>org.hibernate</groupId>
    <artifactId>hibernate-entitymanager</artifactId>
    <version>4.3.0.Final</version>
</dependency>

In Hibenate 3.6 and JPA 2.0 your persistence.xml file would look like this:

<persistence version="2.0"
    xmlns="http://java.sun.com/xml/ns/persistence"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_2_0.xsd">
  <persistence-unit name="myunitname" transaction-type="JTA">
    <provider>org.hibernate.ejb.HibernatePersistence</provider>
        ...
  </persistence-unit>
</persistence>

Now with Hibernate 4.3 You must update your persitence version and your provider class:

<persistence version="2.1" 
     xmlns="http://xmlns.jcp.org/xml/ns/persistence"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence/persistence_2_1.xsd">
  <persistence-unit name="myunitname" transaction-type="JTA">
    <provider>org.hibernate.jpa.HibernatePersistenceProvider</provider>
    <jta-data-source>jdbc/my-data-source</jta-data-source>
    <properties>
      <property name="hibernate.transaction.jta.platform" value="org.hibernate.service.jta.platform.internal.SunOneJtaPlatform" />
        ...
    </properties>
  </persistence-unit>
</persistence>

Note the addition of the property hibernate.transaction.jta.platform This is required and the value will change depending on your container. For Glassfish it's org.hibernate.service.jta.platform.internal.SunOneJtaPlatform. See here for other platform implementations: http://docs.jboss.org/hibernate/core/4.0/javadocs/org/hibernate/service/jta/platform/internal/package-summary.html