Improve robustness of HibernateJpaParametersParameterAccessor.

This change avoids errors when no transactional EntityManager is available.

Closes #2540
Original pull request #2542

Author: cigaly

src/main/java/org/springframework/data/jpa/provider/HibernateJpaParametersParameterAccessor.java

@@ -17,7 +17,7 @@
 
 import javax.persistence.EntityManager;
 
-import org.hibernate.Session;
+import org.hibernate.SessionFactory;
 import org.hibernate.TypeHelper;
 import org.hibernate.jpa.TypedParameterValue;
 import org.hibernate.type.Type;
@@ -50,8 +50,7 @@ class HibernateJpaParametersParameterAccessor extends JpaParametersParameterAcce
 
 		super(parameters, values);
 
-		Session session = em.unwrap(Session.class);
-		this.typeHelper = session.getSessionFactory().getTypeHelper();
+		this.typeHelper = em.getEntityManagerFactory().unwrap(SessionFactory.class).getTypeHelper();
 	}
 
 	@Override

src/test/java/org/springframework/data/jpa/provider/HibernateJpaParametersParameterAccessorUnitTests.java

@@ -0,0 +1,49 @@
+package org.springframework.data.jpa.provider;
+
+import java.lang.reflect.Method;
+
+import javax.persistence.EntityManager;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.data.jpa.repository.query.JpaParameters;
+import org.springframework.test.context.ContextConfiguration;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+import org.springframework.transaction.PlatformTransactionManager;
+import org.springframework.transaction.TransactionStatus;
+import org.springframework.transaction.support.DefaultTransactionDefinition;
+
+@ExtendWith(SpringExtension.class)
+@ContextConfiguration("classpath:hjppa-test.xml")
+public class HibernateJpaParametersParameterAccessorUnitTests {
+
+	@Autowired private EntityManager em;
+
+	@Autowired private PlatformTransactionManager transactionManager;
+
+	@Test
+	void withoutTransaction() throws NoSuchMethodException {
+		simpleTest();
+	}
+
+	@Test
+	void withinTransaction() throws Exception {
+		final TransactionStatus tx = transactionManager.getTransaction(new DefaultTransactionDefinition());
+		try {
+			simpleTest();
+		} finally {
+			transactionManager.rollback(tx);
+		}
+	}
+
+	private void simpleTest() throws NoSuchMethodException {
+		final Method method = EntityManager.class.getMethod("flush");
+		final JpaParameters parameters = new JpaParameters(method);
+		final HibernateJpaParametersParameterAccessor accessor = new HibernateJpaParametersParameterAccessor(parameters,
+				new Object[] {}, em);
+		Assertions.assertEquals(0, accessor.getValues().length);
+		Assertions.assertEquals(parameters, accessor.getParameters());
+	}
+}

src/test/resources/hjppa-test.xml

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<beans xmlns="http://www.springframework.org/schema/beans"
+       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+       xmlns:jdbc="http://www.springframework.org/schema/jdbc"
+       xsi:schemaLocation="http://www.springframework.org/schema/jdbc https://www.springframework.org/schema/jdbc/spring-jdbc.xsd
+		http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd">
+
+    <bean id="entityManagerFactory"
+          class="org.springframework.orm.hibernate5.LocalSessionFactoryBean">
+        <property name="dataSource" ref="dataSource" />
+        <property name="packagesToScan">
+            <array>
+                <value>org.springframework.data.jpa.domain</value>
+                <value>org.springframework.data.jpa.domain.sample</value>
+            </array>
+        </property>
+    </bean>
+
+    <bean id="transactionManager" class="org.springframework.orm.jpa.JpaTransactionManager">
+        <property name="entityManagerFactory" ref="entityManagerFactory" />
+    </bean>
+
+    <bean id="defaultEntityManager"
+          class="org.springframework.orm.jpa.support.SharedEntityManagerBean">
+        <property name="entityManagerFactory" ref="entityManagerFactory" />
+        <property name="synchronizedWithTransaction" value="true" />
+    </bean>
+
+    <jdbc:embedded-database id="dataSource" type="HSQL" generate-name="true">
+        <jdbc:script execution="INIT" separator="/;" location="classpath:scripts/hsqldb-init.sql"/>
+        <jdbc:script execution="INIT" separator="/;" location="classpath:scripts/schema-stored-procedures.sql"/>
+    </jdbc:embedded-database>
+</beans>