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" eg 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?

    • 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.

    JPA是舞蹈，Hibernate是舞蹈演员。

    Some things are too hard to understand without a historical perspective of the language and understanding of the JCP.

    Often there are third parties that develop packages that perform a function or fill a gap that are not part of the official JDK. For various reasons that function may become part of the Java JDK through the JCP (Java Community Process)

    Hibernate (in 2003) provided a way to abstract SQL and allow developers to think more in terms of persisting objects (ORM). You notify hibernate about your Entity objects and it automatically generates the strategy to persist them. Hibernate provided an implementation to do this and the API to drive the implementation either through XML config or annotations.

    The fundamental issue now is that your code becomes tightly coupled with a specific vendor(Hibernate) for what a lot of people thought should be more generic. Hence the need for a generic persistence API.

    Meanwhile, the JCP with a lot of input from Hibernate and other ORM tool vendors was developing JSR 220 (Java Specification Request) which resulted in JPA 1.0 (2006) and eventually JSR 317 which is JPA 2.0 (2009). These are specifications of a generic Java Persistence API. The API is provided in the JDK as a set of interfaces so that your classes can depend on the javax.persistence and not worry about the particular vendor that is doing the work of persisting your objects. This is only the API and not the implementation. Hibernate now becomes one of the many vendors that implement the JPA 2.0 specification. You can code toward JPA and pick whatever compliant ORM vendor suits your needs.

    There are cases where Hibernate may give you features that are not codified in JPA. In this case, you can choose to insert a Hibernate specific annotation directly in your class since JPA does not provide the interface to do that thing.

    Source: http://www.reddit.com/r/java/comments/16ovek/understanding_when_to_use_jpa_vs_hibernate/

    链接地址: http://www.djcxy.com/p/37008.html

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