Can hibernate register an entity class dynamiclly without recreating the session factory in runtime?

No. The bootstrap process creates the Metadata and passes it to the SessionFactory upon instantiation. For this reason, you can not add entities dynamically to a SessionFactory, meaning that you need to recreate it from scratch.

However, the SessionFactory initialization can be done programmatically so you can recreate it whenever you have new entities that need to be registered.

Firstly, thank you very much for your gentle response.
One more question, After creating a new SessionFactory, shall I close the old one? If I do, will all the sessions and transactions related to it throw exceptions at this time? How can I get a smooth transition while trying to rebuild a SessionFactory?

You should close the old SessionFactory because and deallocate all its resources (e.g. connection pool, caches, metadata). Related to that transition, you could probably orchestrate it in your application code. Hibernate does not offer anything for this particular use case.