What's the difference between JPA and Hibernate?
I understand that JPA 2 is a specification and Hibernate is a tool for ORM. Also, I understand that Hibernate has more features than JPA 2. But from a practical point of view, what really is the difference?
I have experience using iBatis and now I'm trying to learn either Hibernate or JPA2. I picked up Pro JPA2 book and it keeps referring to "JPA provider". For example:
If you think a feature should be standardized, you should speak up and request it from your JPA provider
This confuses me so I have a few questions:
- Using JPA2 alone can I fetch data from DB by simply annotating my POJO's
- Is JPA2 supposed to be used with a "JPA Provider" e.g TopLink or Hibernate? If so, then what's the benefit of using JPA2 + Hibernate as compared to JPA2 alone, or compared to Hibernate alone ?
- Can you recommend a good practical JPA2 book. "Pro JPA2" seems more like a bible and reference on JPA2 (It doesn't get into Queries until the later half of the book). Is there a book that takes a problem/solution approach to JPA2?
Answer
As you state JPA is just a specification, meaning there is no implementation. You can annotate your classes as much as you would like with JPA annotations, however without an implementation nothing will happen. Think of JPA as the guidelines that must be followed or an interface, while Hibernate's JPA implementation is code that meets the API as defined by the JPA specification and provides the under the hood functionality.
When you use Hibernate with JPA you are actually using the Hibernate JPA implementation. The benefit of this is that you can swap out Hibernate's implementation of JPA for another implementation of the JPA specification. When you use straight Hibernate you are locking into the implementation because other ORMs may use different methods/configurations and annotations, therefore you cannot just switch over to another ORM.
For a more detailed description read my blog entry.