Tolerate Hibernate 5.2

[garethpowell]

Whilst trying to upgrade our application to use Spring Boot 2.1.0 I hit upon a problem when Hibernate initialises. We are currently tied to using Hibernate 5.2.x and so far as I can tell Spring Boot 2.1.0 should still support this version. However, there appears to be an explicit dependency on Hibernate 5.3.x during the Spring Boot JPA auto-configuration. With Hibernate 5.2.x when the HibernateJpaConfiguration class executes to bootstrap Hibernate, a ClassNotFoundException is thrown as it's unable to locate the new to Hibernate 5.3.x class BeanContainer.

Caused by: java.lang.ClassNotFoundException: org.hibernate.resource.beans.container.spi.BeanContainer
	at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583)
	at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178)
	at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521)
	... 45 common frames omitted

The problem looks to be in the HibernateJpaConfiguration.determineHibernatePropertiesCustomizers method where it instantiates a SpringBeanContainer.

I have attached a super simple project generated from the Spring Initializr that demonstrates the problem. The only change I made following project creation was to set the property hibernate.version to be 5.2.17.Final. Simply run the Maven build or start up the app to see the problem.

Having taken a look at the sources, there appears to be no conditional check during initialization to establish whether the BeanContainer class is available. I think we need something similar to what can be found in LocalSessionFactoryBean

	@Override
	public void setBeanFactory(BeanFactory beanFactory) {
		if (beanFactory instanceof ConfigurableListableBeanFactory &&
				ClassUtils.isPresent("org.hibernate.resource.beans.container.spi.BeanContainer",
						getClass().getClassLoader())) {
			this.beanFactory = (ConfigurableListableBeanFactory) beanFactory;
		}
	}

spring-boot-hibernate-problem-demo.zip

[wilkinsona]

We can consider making this conditional, but please note that we generally try to avoid writing code to support multiple minor versions of the same dependency, particularly minor versions that are earlier than the version that we compile against.

so far as I can tell Spring Boot 2.1.0 should still support this version

Can you please point to the source of that impression? I'd like to make sure that our documentation isn't misleading.

[philwebb]

@garethpowell Is there anything specific blocking you from upgrading to Hibernate 5.3?

[wilkinsona]

It's not just BeanContainer. We also use RegionFactoryTemplate which is another 5.3 addition.

[wilkinsona]

Actually, it's not us, but a different Hibernate module. That shows the difficulty in testing that we're 5.2 compatible when 5.3 is on the classpath.

[garethpowell]

@wilkinsona I suppose I inferred that Spring Boot would/should continue to support older versions of Hibernate based on the support from Spring 5.x. I don't think Spring Boot should force that particular upgrade on users as there are significant changes between 5.2 and 5.3 in particular the Caching SPI, and it's for this reason we can't simply upgrade to 5.3 at the moment @philwebb. We are using Elasticache in AWS as the backend and the library supporting this is not available for Hibernate 5.3 yet. I have been looking for alternatives, but so far haven't found a suitable one.

As of Spring Framework 5.0, Spring requires Hibernate ORM 4.3 or later for JPA support and even Hibernate ORM 5.0+ for programming against the native Hibernate Session API. Note that the Hibernate team does not maintain any versions prior to 5.1 anymore and is likely to focus on 5.3+ exclusively soon.

[wilkinsona]

Spring Boot takes a more opinionated view of things than Spring Framework so you can't safely assume that because Framework supports a particular range of versions of a dependency that Boot will do the same.

Generally speaking, third-party projects focus on backwards compatibility rather than forwards compatibility. This means that it will usually be safe to override Boot's dependency management to upgrade to a new minor release but that an override that downgrades to an older minor version may not work.

This feels to me more like an issue for the Elasticache Hibernate integration. Have you considered sticking on Boot 2.0.x until they have implemented Hibernate 5.3 compatibility?

[garethpowell]

As an organisation we endeavour to to keep up to date with Spring and other core libraries as new versions become available, thus avoiding any big bang changes. I appreciate the opinionated approach of Spring Boot and this works marvelously for the most part. I could understand support for pre 5.x Hibernate compatibility being dropped, but I can't help but think that this is going to prevent a large number of people upgrading to Spring Boot 2.1 if they're also forced to update to Hibernate 5.3. Anyway, we'll be staying on Boot 2.0 for at least awhile yet then. Thanks for your prompt response to this issue.