Change HibernateJpaConfiguration to public to be able to extend it

[damienbeaufils]

Hello,

Since this commit, we can't extend anymore HibernateJpaAutoConfiguration class to specify hibernate mapping files like this, but we can’t either extend HibernateJpaConfiguration class because it is package-protected.
This PR changes HibernateJpaConfiguration class modifier to public to be able to extend it.
It could be a solution for this question on SO.

Thanks!

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[snicoll]

@damienbeaufils extending from an auto-configuration isn't really a great idea. Can we take a step back and discuss why you need to do this? Perhaps we can adapt the auto-configuration to take that use case into account.

[damienbeaufils]

@snicoll I agree extending from an autoconfiguration is not great.
My use case is quite simple I think: I would like to configure the Hibernate JPA datasource provided by Spring Boot with specific XML mapping files.
The way people found is to override the LocalContainerEntityManagerFactoryBean bean from the old HibernateJpaAutoConfiguration and set mapping resources.

[snicoll]

Can you show an example of such override please?

[damienbeaufils]

Sure. An example:

@Configuration
public class MappingsConfiguration extends HibernateJpaAutoConfiguration {

    public MappingsConfiguration(DataSource dataSource, JpaProperties jpaProperties, ObjectProvider<JtaTransactionManager> jtaTransactionManager, ObjectProvider<TransactionManagerCustomizers> transactionManagerCustomizers, ObjectProvider<List<SchemaManagementProvider>> providers) {
        super(dataSource, jpaProperties, jtaTransactionManager, transactionManagerCustomizers, providers);
    }

    @Bean
    @Override
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(EntityManagerFactoryBuilder factoryBuilder) {
        LocalContainerEntityManagerFactoryBean localContainerEntityManagerFactoryBean = getSuperEntityManagerFactory(factoryBuilder);
        localContainerEntityManagerFactoryBean.setMappingResources(
                "db/mappings/dummy.xml"
        );
        return localContainerEntityManagerFactoryBean;
    }

    LocalContainerEntityManagerFactoryBean getSuperEntityManagerFactory(EntityManagerFactoryBuilder factoryBuilder) {
        return super.entityManagerFactory(factoryBuilder);
    }
}

If you need a whole project using this code, see this repository.

[wilkinsona]

This feels like the sort of thing that we've previously solved with a customizer interface. If we consider this to be too much of an edge case to warrant that, a bean post-processor could be used instead.

[damienbeaufils]

@wilkinsona Do you have an example of a customizer interface somewhere?

[wilkinsona]

JacksonObjectMappingBuilderCustomizer is one example. It's used by JacksonAutoConfiguration.

[snicoll]

perhaps mappingResources could be a spring.jpa property somehow. That would remove that need altogether (although I agree the customizer is typically what we do in such cases).

[wilkinsona]

I like that idea, @snicoll. The method just takes String… so a List<String> spring.jpa.mapping-resources property would seem to fit nicely.

[snicoll]

Cool.

@damienbeaufils I am not keen to change the scope of that class (extending the AutoConfiguration is kind of a smell anyway). Let's add support for this in #10684. If you find other use cases where extending is necessary we can go the customizer route.

[damienbeaufils]

@snicoll I'm fine with this solution. Thanks! If you need any feedback for #10684 before the next milestone release, feel free to ask.