- Add new configuration setting ALLOW_JTA_TRANSACTION_ACCESS. Uses can use this setting to

override default JPA behavior for transaction access if needed.
- Added new SPI method accessTransaction() which bypasses checks and returns the current or new transaction.

hibernate-core/src/main/java/org/hibernate/boot/internal/SessionFactoryBuilderImpl.java

@@ -60,6 +60,7 @@ import org.hibernate.tuple.entity.EntityTuplizerFactory;
 import org.jboss.logging.Logger;
 
 import static org.hibernate.cfg.AvailableSettings.ACQUIRE_CONNECTIONS;
+import static org.hibernate.cfg.AvailableSettings.ALLOW_JTA_TRANSACTION_ACCESS;
 import static org.hibernate.cfg.AvailableSettings.AUTO_CLOSE_SESSION;
 import static org.hibernate.cfg.AvailableSettings.AUTO_EVICT_COLLECTION_CACHE;
 import static org.hibernate.cfg.AvailableSettings.AUTO_SESSION_EVENTS_LISTENER;
@@ -480,6 +481,11 @@ public class SessionFactoryBuilderImpl implements SessionFactoryBuilderImplement
 		this.options.jpaBootstrap = true;
 	}
 
+	@Override
+	public void disableJtaTransactionAccess() {
+		this.options.jtaTransactionAccessEnabled = false;
+	}
+
 	@Override
 	public SessionFactoryOptions buildSessionFactoryOptions() {
 		return new SessionFactoryOptionsImpl( this );
@@ -504,6 +510,7 @@ public class SessionFactoryBuilderImpl implements SessionFactoryBuilderImplement
 		// Session behavior
 		private boolean flushBeforeCompletionEnabled;
 		private boolean autoCloseSessionEnabled;
+		private boolean jtaTransactionAccessEnabled;
 
 		// (JTA) transaction handling
 		private boolean jtaTrackByThread;
@@ -594,6 +601,11 @@ public class SessionFactoryBuilderImpl implements SessionFactoryBuilderImplement
 					BOOLEAN,
 					true
 			);
+			this.jtaTransactionAccessEnabled = cfgService.getSetting(
+					ALLOW_JTA_TRANSACTION_ACCESS,
+					BOOLEAN,
+					true
+			);
 
 			this.flushBeforeCompletionEnabled = cfgService.getSetting( FLUSH_BEFORE_COMPLETION, BOOLEAN, true );
 			this.autoCloseSessionEnabled = cfgService.getSetting( AUTO_CLOSE_SESSION, BOOLEAN, false );
@@ -848,6 +860,11 @@ public class SessionFactoryBuilderImpl implements SessionFactoryBuilderImplement
 			return jpaBootstrap;
 		}
 
+		@Override
+		public boolean isJtaTransactionAccessEnabled() {
+			return jtaTransactionAccessEnabled;
+		}
+
 		@Override
 		public Object getBeanManagerReference() {
 			return beanManagerReference;
@@ -1134,6 +1151,11 @@ public class SessionFactoryBuilderImpl implements SessionFactoryBuilderImplement
 		return options.isJpaBootstrap();
 	}
 
+	@Override
+	public boolean isJtaTransactionAccessEnabled() {
+		return options.isJtaTransactionAccessEnabled();
+	}
+
 	@Override
 	public Object getBeanManagerReference() {
 		return options.getBeanManagerReference();

hibernate-core/src/main/java/org/hibernate/boot/internal/SessionFactoryOptionsImpl.java

@@ -51,6 +51,7 @@ public class SessionFactoryOptionsImpl implements SessionFactoryOptions {
 	// Session behavior
 	private final boolean flushBeforeCompletionEnabled;
 	private final boolean autoCloseSessionEnabled;
+	private boolean jtaTransactionAccessEnabled;
 
 	// transaction handling
 	private final boolean jtaTrackByThread;
@@ -124,6 +125,7 @@ public class SessionFactoryOptionsImpl implements SessionFactoryOptions {
 		this.validatorFactoryReference = state.getValidatorFactoryReference();
 
 		this.jpaBootstrap = state.isJpaBootstrap();
+		this.jtaTransactionAccessEnabled = state.isJtaTransactionAccessEnabled();
 		this.sessionFactoryName = state.getSessionFactoryName();
 		this.sessionFactoryNameAlsoJndiName = state.isSessionFactoryNameAlsoJndiName();
 
@@ -197,6 +199,11 @@ public class SessionFactoryOptionsImpl implements SessionFactoryOptions {
 		return jpaBootstrap;
 	}
 
+	@Override
+	public boolean isJtaTransactionAccessEnabled() {
+		return jtaTransactionAccessEnabled;
+	}
+
 	@Override
 	public Object getBeanManagerReference() {
 		return beanManagerReference;

hibernate-core/src/main/java/org/hibernate/boot/internal/SessionFactoryOptionsState.java

@@ -46,6 +46,8 @@ public interface SessionFactoryOptionsState {
 	@Deprecated
 	boolean isJpaBootstrap();
 
+	boolean isJtaTransactionAccessEnabled();
+
 	Object getBeanManagerReference();
 
 	Object getValidatorFactoryReference();

hibernate-core/src/main/java/org/hibernate/boot/spi/AbstractDelegatingSessionFactoryOptions.java

@@ -53,6 +53,11 @@ public class AbstractDelegatingSessionFactoryOptions implements SessionFactoryOp
 		return delegate.isJpaBootstrap();
 	}
 
+	@Override
+	public boolean isJtaTransactionAccessEnabled() {
+		return delegate.isJtaTransactionAccessEnabled();
+	}
+
 	@Override
 	public Object getBeanManagerReference() {
 		return delegate.getBeanManagerReference();

hibernate-core/src/main/java/org/hibernate/boot/spi/SessionFactoryBuilderImplementor.java

@@ -28,6 +28,8 @@ public interface SessionFactoryBuilderImplementor extends SessionFactoryBuilder
 	@Deprecated
 	void markAsJpaBootstrap();
 
+	void disableJtaTransactionAccess();
+
 	/**
 	 * Build the SessionFactoryOptions that will ultimately be passed to SessionFactoryImpl constructor.
 	 *

hibernate-core/src/main/java/org/hibernate/boot/spi/SessionFactoryOptions.java

@@ -58,6 +58,8 @@ public interface SessionFactoryOptions {
 	@Deprecated
 	boolean isJpaBootstrap();
 
+	boolean isJtaTransactionAccessEnabled();
+
 	/**
 	 * The name to be used for the SessionFactory.  This is use both in:<ul>
 	 *     <li>in-VM serialization</li>

hibernate-core/src/main/java/org/hibernate/cfg/AvailableSettings.java

@@ -1463,4 +1463,15 @@ public interface AvailableSettings {
 	 * @since 5.1
 	 */
 	String CREATE_EMPTY_COMPOSITES_ENABLED = "hibernate.create_empty_composites.enabled";
+
+	/**
+	 * Setting that allows access to the underlying {@link org.hibernate.Transaction}, even
+	 * when using a JTA since normal JPA operations prohibit this behavior.
+	 * <p/>
+	 * Values are {@code true} grants access, {@code false} does not.
+	 * <p/>
+	 * The default behavior is to allow access unless the session is bootstrapped via JPA.
+	 */
+	String ALLOW_JTA_TRANSACTION_ACCESS = "hibernate.jta.allowTransactionAccess";
+
 }

hibernate-core/src/main/java/org/hibernate/engine/spi/SessionDelegatorBaseImpl.java

@@ -433,6 +433,11 @@ public class SessionDelegatorBaseImpl implements SessionImplementor {
 		return delegate.getEventListenerManager();
 	}
 
+	@Override
+	public Transaction accessTransaction() {
+		return delegate.accessTransaction();
+	}
+
 	@Override
 	public Transaction beginTransaction() {
 		return delegate.beginTransaction();

hibernate-core/src/main/java/org/hibernate/engine/spi/SharedSessionContractImplementor.java

@@ -21,6 +21,7 @@ import org.hibernate.Interceptor;
 import org.hibernate.ScrollMode;
 import org.hibernate.ScrollableResults;
 import org.hibernate.SharedSessionContract;
+import org.hibernate.Transaction;
 import org.hibernate.collection.spi.PersistentCollection;
 import org.hibernate.engine.jdbc.LobCreationContext;
 import org.hibernate.engine.jdbc.spi.JdbcCoordinator;
@@ -150,6 +151,15 @@ public interface SharedSessionContractImplementor
 	 */
 	boolean isTransactionInProgress();
 
+	/**
+	 * Provides access to the underlying transaction or creates a new transaction if
+	 * one does not already exist or is active.  This is primarily for internal or
+	 * integrator use.
+	 *
+	 * @return the transaction
+     */
+	Transaction accessTransaction();
+
 	/**
 	 * Hide the changing requirements of entity key creation
 	 *

hibernate-core/src/main/java/org/hibernate/internal/AbstractSharedSessionContract.java

@@ -352,37 +352,29 @@ public abstract class AbstractSharedSessionContract implements SharedSessionCont
 		if ( getFactory().getSessionFactoryOptions().isJpaBootstrap() ) {
 			// JPA requires that we throw IllegalStateException if this is called
 			// on a JTA EntityManager
-			//
-			// todo : ultimately add an option for allowing users to access the Transaction in JTA cases too like classic Hibernate
-
 			if ( getTransactionCoordinator().getTransactionCoordinatorBuilder().isJta() ) {
-				throw new IllegalStateException( "A JTA EntityManager cannot use getTransaction()" );
+				if ( !getFactory().getSessionFactoryOptions().isJtaTransactionAccessEnabled() ) {
+					throw new IllegalStateException( "A JTA EntityManager cannot use getTransaction()" );
+				}
 			}
-
-			if ( this.currentHibernateTransaction == null ) {
-				this.currentHibernateTransaction = new TransactionImpl(
-						getTransactionCoordinator(),
-						getExceptionConverter()
-				);
-			}
-			if ( !isClosed() ) {
-				getTransactionCoordinator().pulse();
-			}
-			return currentHibernateTransaction;
 		}
-		else {
-			// Historically Hibernate would not allow access to the Transaction after the Session is closed
-			checkOpen();
+		return accessTransaction();
+	}
 
-			if ( this.currentHibernateTransaction == null || this.currentHibernateTransaction.getStatus() != TransactionStatus.ACTIVE ) {
-				this.currentHibernateTransaction = new TransactionImpl(
-						getTransactionCoordinator(),
-						getExceptionConverter()
-				);
-			}
+	@Override
+	public Transaction accessTransaction() {
+		checkOpen();
+		if ( this.currentHibernateTransaction == null || this.currentHibernateTransaction.getStatus() != TransactionStatus.ACTIVE ) {
+			this.currentHibernateTransaction = new TransactionImpl(
+					getTransactionCoordinator(),
+					getExceptionConverter()
+			);
+
+		}
+		if ( !isClosed() ) {
 			getTransactionCoordinator().pulse();
-			return currentHibernateTransaction;
 		}
+		return this.currentHibernateTransaction;
 	}
 
 	@Override

hibernate-core/src/main/java/org/hibernate/jpa/AvailableSettings.java

@@ -346,4 +346,14 @@ public interface AvailableSettings {
 	 * @since 5.0.8
 	 */
 	String DELAY_CDI_ACCESS = "hibernate.delay_cdi_access";
+
+	/**
+	 * Setting that allows access to the underlying {@link org.hibernate.Transaction}, even
+	 * when using a JTA since normal JPA operations prohibit this behavior.
+	 * <p/>
+	 * Values are {@code true} grants access, {@code false} does not.
+	 * <p/>
+	 * The default behavior is to allow access unless the session is bootstrapped via JPA.
+	 */
+	String ALLOW_JTA_TRANSACTION_ACCESS = "hibernate.jta.allowTransactionAccess";
 }

hibernate-core/src/main/java/org/hibernate/jpa/boot/internal/EntityManagerFactoryBuilderImpl.java

@@ -881,6 +881,12 @@ public class EntityManagerFactoryBuilderImpl implements EntityManagerFactoryBuil
 //			sfBuilder.applyInterceptor( sessionFactoryInterceptor );
 //		}
 
+		// will use user override value or default to false if not supplied to follow JPA spec.
+		final boolean jtaTransactionAccessEnabled = readBooleanConfigurationValue( AvailableSettings.ALLOW_JTA_TRANSACTION_ACCESS );
+		if ( !jtaTransactionAccessEnabled ) {
+			( ( SessionFactoryBuilderImplementor ) sfBuilder ).disableJtaTransactionAccess();
+		}
+
 		// Locate and apply any requested SessionFactoryObserver
 		final Object sessionFactoryObserverSetting = configurationValues.remove( AvailableSettings.SESSION_FACTORY_OBSERVER );
 		if ( sessionFactoryObserverSetting != null ) {