Derive StatelessSession from primary Session in HibernateJpaDialect

This is analogous to LocalSessionFactoryBean's SpringSessionContext.

See gh-36025

spring-orm/src/main/java/org/springframework/orm/jpa/DefaultJpaDialect.java

@@ -18,6 +18,7 @@ package org.springframework.orm.jpa;
 
 import java.io.Serializable;
 import java.sql.SQLException;
+import java.util.Map;
 
 import jakarta.persistence.EntityManager;
 import jakarta.persistence.PersistenceException;
@@ -113,6 +114,27 @@ public class DefaultJpaDialect implements JpaDialect, Serializable {
 			throws PersistenceException, SQLException {
 	}
 
+	/**
+	 * Derive a new {@code EntityAgent} from the given {@code EntityManager} if possible,
+	 * sharing the transactional context.
+	 * <p><b>NOTE: This method is designed for Spring's early JPA 4.0 support.</b>
+	 * For JPA 3.2 compatibility, the return type cannot be enforced as
+	 * {@code jakarta.persistence.EntityAgent}. Subclasses should override it with
+	 * their specific EntityAgent type if possible, or otherwise just EntityAgent,
+	 * as a covariant return type. This will make it forward-compatible with a
+	 * future variant of this method in the {@link JpaDialect} interface itself.
+	 * @param entityManager the current JPA EntityManager
+	 * @param properties the properties for the EntityAgent, if any
+	 * @return the new EntityAgent instance, or {@code null} if none can be derived
+	 * @throws jakarta.persistence.PersistenceException if thrown by JPA methods
+	 * @since 7.0.4
+	 */
+	public @Nullable Object deriveEntityAgent(EntityManager entityManager, @Nullable Map<?, ?> properties)
+			throws PersistenceException {
+
+		return null;
+	}
+
 
 	//-----------------------------------------------------------------------------------
 	// Hook for exception translation (used by JpaTransactionManager)

spring-orm/src/main/java/org/springframework/orm/jpa/EntityManagerFactoryUtils.java

@@ -334,7 +334,15 @@ public abstract class EntityManagerFactoryUtils {
 
 		// Create a new EntityManager for use within the current transaction.
 		logger.debug("Opening JPA EntityAgent");
-		Object entityAgent = createEntityAgent(emf, properties);
+		Object entityAgent = null;
+		if (emHolder != null && emf instanceof EntityManagerFactoryInfo info &&
+				info.getJpaDialect() instanceof DefaultJpaDialect defaultJpaDialect) {
+			// For JpaTransactionManager: share transaction context with primary EntityManager.
+			entityAgent = defaultJpaDialect.deriveEntityAgent(emHolder.getEntityManager(), properties);
+		}
+		if (entityAgent == null) {
+			entityAgent = createEntityAgent(emf, properties);
+		}
 
 		if (emHolder != null) {
 			emHolder.setEntityAgent(entityAgent);

spring-orm/src/main/java/org/springframework/orm/jpa/vendor/HibernateJpaDialect.java

@@ -16,8 +16,10 @@
 
 package org.springframework.orm.jpa.vendor;
 
+import java.lang.reflect.Method;
 import java.sql.Connection;
 import java.sql.SQLException;
+import java.util.Map;
 
 import jakarta.persistence.EntityManager;
 import jakarta.persistence.PersistenceException;
@@ -25,6 +27,7 @@ import org.hibernate.ConnectionReleaseMode;
 import org.hibernate.FlushMode;
 import org.hibernate.JDBCException;
 import org.hibernate.Session;
+import org.hibernate.StatelessSession;
 import org.hibernate.engine.spi.SessionImplementor;
 import org.jspecify.annotations.Nullable;
 
@@ -39,10 +42,12 @@ import org.springframework.transaction.InvalidIsolationLevelException;
 import org.springframework.transaction.TransactionDefinition;
 import org.springframework.transaction.TransactionException;
 import org.springframework.transaction.support.ResourceTransactionDefinition;
+import org.springframework.util.ClassUtils;
+import org.springframework.util.ReflectionUtils;
 
 /**
  * {@link org.springframework.orm.jpa.JpaDialect} implementation for Hibernate.
- * Compatible with Hibernate ORM 7.x.
+ * Compatible with Hibernate ORM 7.x and 8.x.
  *
  * @author Juergen Hoeller
  * @author Costin Leau
@@ -54,6 +59,10 @@ import org.springframework.transaction.support.ResourceTransactionDefinition;
 @SuppressWarnings("serial")
 public class HibernateJpaDialect extends DefaultJpaDialect {
 
+	/** Hibernate 8.0: inherited setProperty(String, Object) method from JPA 4.0 EntityAgent. */
+	private static final @Nullable Method STATELESS_SESSION_SET_PROPERTY = ClassUtils.getMethodIfAvailable(
+			StatelessSession.class, "setProperty", String.class, Object.class);
+
 	private final HibernateExceptionTranslator exceptionTranslator = new HibernateExceptionTranslator();
 
 	boolean prepareConnection = true;
@@ -194,6 +203,21 @@ public class HibernateJpaDialect extends DefaultJpaDialect {
 		return new HibernateConnectionHandle(entityManager.unwrap(SessionImplementor.class));
 	}
 
+	@Override
+	public StatelessSession deriveEntityAgent(EntityManager entityManager, @Nullable Map<?, ?> properties)
+			throws PersistenceException {
+
+		StatelessSession entityAgent = entityManager.unwrap(Session.class).statelessWithOptions().connection().open();
+		if (properties != null && STATELESS_SESSION_SET_PROPERTY != null) {
+			for (Map.Entry<?, ?> entry : properties.entrySet()) {
+				if (entry.getKey() instanceof String key) {
+					ReflectionUtils.invokeMethod(STATELESS_SESSION_SET_PROPERTY, entityAgent, key, entry.getValue());
+				}
+			}
+		}
+		return entityAgent;
+	}
+
 	@Override
 	public @Nullable DataAccessException translateExceptionIfPossible(RuntimeException ex) {
 		return this.exceptionTranslator.translateExceptionIfPossible(ex);

spring-orm/src/main/java/org/springframework/orm/jpa/vendor/HibernateJpaVendorAdapter.java

@@ -50,7 +50,7 @@ import org.springframework.transaction.jta.JtaTransactionManager;
 
 /**
  * {@link org.springframework.orm.jpa.JpaVendorAdapter} implementation for Hibernate.
- * Compatible with Hibernate ORM 7.x.
+ * Compatible with Hibernate ORM 7.x and 8.x.
  *
  * <p>Exposes Hibernate's persistence provider and Hibernate's Session as extended
  * EntityManager interface, and adapts {@link AbstractJpaVendorAdapter}'s common