What's the difference between JPA and Hibernat

Question

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 1

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.

Answer 2

JPA is the interface, Hibernate is one implementation of that interface.

Answer 3

JPA is a specification that you implement in your data layer to perform db opertations, OR mappings and other required tasks.

Since it is just a specification, you need a tool to have it implemented. That tool can be either Hibernate, TopLink, iBatis, spring-data etc.

You don't necessarily require JPA if you are using Hibernate in your Data Layer. But if you use JPA specification for Hibernate, then it will make switching to other ORM tools like iBatis, TopLink easy in future, because the specification is common for others as well.

*(if you remember, you do import javax.persistence.*; when you use annotations for OR mapping (like @Id, @Column, @GeneratedValue etc.) in Hibernate, that's where you are using JPA under Hibernate, you can use JPA's @Query & other features as well)

Answer 4

JPA is just a specification which needs concrete implementation. The default implementation provided by oracle is "Eclipselink" now. Toplink is donated by Oracle to Eclipse foundation to merge with eclipselink.

Using Eclipselink, one can be sure that the code is portable to any implementation if need arises. Hibernate is also a full JPA implementation + MORE. Hibernate is super set of JPA with some extra Hibernate specific functionality. So application developed in Hibernate may not be compatible when switched to other implementation. Still hibernate is choice of majority of developers as JPA implementation and widely used.

Another JPA implementation is OpenJPA, which is an extension of Kodo implementation.

JPA vs Hibernate

Answer 5

JPA is the interface while Hibernate is the implementation.

Traditionally there have been multiple Java ORM solutions:

• Hibernate
• TopLink
• JDO

each implementation defining its own mapping definition or client API. The JPA expert group gathered the best of all these tools and so they created the Java Persistence API standard.

A standard persistence API is very convenient from a client point of view, making it relatively easy to switch one implementation with the other (although in practice it's not that simple because on large projects you'll have to use specific non-standard features anyway).

The standard JPA has pushed Java ORM competition to a new level and this can only lead to better implementations.

As explained in my book, High-Performance Java Persistence, Hibernate offers features that are not yet supported by JPA:

• extended identifier generators (hi/lo, pooled, pooled-lo)
• transparent prepared statement batching
• customizable CRUD (@SQLInsert, @SQLUpdate, @SQLDelete) statements
• static or dynamic collection filters (e.g. @FilterDef, @Filter, @Where) and entity filters (e.g. @Where)
• mapping properties to SQL fragments (e.g. @Formula)
• immutable entities (e.g. @Immutable)
• more flush modes (e.g. FlushMode.MANUAL, FlushMode.ALWAYS)
• querying the second-level cache by the natural key of a given entity
• entity-level cache concurrency strategies (e.g. Cache(usage = CacheConcurrencyStrategy.READ_WRITE))
• versioned bulk updates through HQL
• exclude fields from optimistic locking check (e.g. @OptimisticLock(excluded = true))
• versionless optimistic locking (e.g. OptimisticLockType.ALL, OptimisticLockType.DIRTY)
• support for skipping (without waiting) pessimistic lock requests
• support for Java 8 Date and Time
• support for multitenancy
• support for soft delete (e.g. @Where, @Filter)

These extra features allow Hibernate to address many persistence requirements demanded by large enterprise applications.

Answer 6

JPA is just a specification which needs concrete implementation. The default implementation oracle provide is "Eclipselink" now. (Toplink is donated by Oracle to Eclipse foundation to merge with eclipselink)

(Reference : http://www.oracle.com/technetwork/middleware/toplink/index-085257.html http://www.eclipse.org/org/press-release/20080317_Eclipselink.php )

Using Eclipselink, one can be sure that the code is portable to any implementation if need arises. Hibernate is also a full JPA implementation + MORE ( Sort of JPA Plus). Hibernate is super set of JPA with some extra Hibernate specific functionality. So app developed in Hibernate may not be compatible when switched to other implementation. Still hibernate is choice of majority of developers as JPA implementation and widely used.

Another JPA implementation is OpenJPA (openjpa.apache.org) which is an extension of Kodo implementation.