[hibernate-dev] Standalone service registry

[Karl von Randow]

Hi all,

I had a conversation with Steve today on IRC about refactoring the org.hibernate.service package to make it standalone. The service registry implementation is mostly separable from Hibernate core already, and it could be useful in other applications perhaps where hibernate-core isn’t a dependency. I found myself in that exact situation, which is why I’m here.

I have done a test extraction of the service registry classes, excluding the BootServiceRegistry, ClassLoaderService and StrategySelector families. This was quite straight forward, worked well and worked with Hibernate core.

Steve suggested that the boot service registry and associated class loading functionality would be useful standalone as well. To see what that is like, I have now done a test extraction including the BootServiceRegistry, ClassLoaderService and StrategySelector families. It has worked quite well, but was definitely major.

Part of the discussion that I had with Steve this morning, and the piece that he particularly wanted to discuss here, is how to perform the extraction and where to put it:

* Is this standalone service registry its own project, separate from the hibernate-orm project. Would that make it easier to use in other projects? Or is it a hibernate-ssr module within the hibernate-orm project.

* Is it called hibernate-ssr or perhaps hibernate-serviceregistry? Perhaps the later is more appropriate especially if it’s a separate project.


I think the end result of the extraction I’ve done is pretty good, it does of course modify a number of classes across the hibernate-orm project (mostly just imports, though) so I’m wary that this may not be the best contribution to make as a newcomer! For reference, my WIP is here https://github.com/karlvr/hibernate-orm/compare/ssr
I have done it inside the hibernate-orm project to best preserve the git metadata (e.g. source file renames). The project compiles, tests pass (except for some osgi stuff I don’t yet understand!), and it appears to work when used in a large Hibernate project of mine.

The most interesting parts of migrating BootServiceRegistry et al over to the SSR is the Hibernate ORM dependencies in BootServiceRegistry - specifically Integrators. There were also Hibernate ORM specific features in StrategySelectorBuilder and ClassLoaderServiceImpl (specifically ClassLoaderHelper). I have created subclasses in hibernate-core of the implementations I moved to the SSR module, with the same class name as the original. These subclasses provide the Hibernate specific functionality.

Another interesting standalone issue is the exception hierarchy. The exceptions no longer extend from HibernateException. Perhaps it would be possible to have that class in the SSR package and core to address this.

I would be proud to contribute this change. I’m happy to make any changes, and I will definitely tidy up my commit messages to meet the contribution guidelines! Likewise I’m happy to throw away the work if it’s not the right approach. I had a pretty good fun morning anyway :-)

Best regards,
Karl