How to find a way to get the DataSource object from the EntityManager in Hibernate

Issue

• We don't have a custom mapping capability in the JPA specification.
• We need help to build a Spring JdbcTemplate object when only have a reference to the entity manager.

• In other words, if we have a reference to an EntityManager for my persistence unit, how to get the data source (even use JBoss specific APIs) so that we can create a JdbcTemplate object.

• In otherwords imagine:

EntityManager em = ...
JdbcTemplate springTempalte = new JdbcTemplate( em.getDatasource() );

• We would be able to use the spring template.
• The problem is that we cannot find a way to get to the data source from the entity manager.
• We don't want to reference the data source directly, since there can be multiple persistence units linked to different data-sources and we want that configuration all in one place.
• What API calls (even JBoss specific) can we make to get the data source used in a given EntityManager in JBoss EAP 6.3.
• We need to know how to get to the data-source, but lets know what SqlResultSetMapping is and whether we can have a custom implementation that does the mapping instead of using the annotation class?
• Can please provide us JBoss specific or Hibernate APIs that help us go from the JBoss EntityManager implementation to the underlying data source ?
• We are okay to cast that object to a JBoss specific or hibernate specific implementation that we can guarantee exists in EAP 6.4+.