How to use JPA API Specification?

Hey, this is my first article here. I hope that I'll be able to post content about technology more consistently from now on.

I've chosen to bring you an advanced JPA 2 topic: the Specification API.

Specification was a concept that Eric Evans brought up in his book Domain Driven Design(DDD). Based on this, JPA brings this concept as a set of interfaces that facilitate the reuse of predicates, using the Criteria API. That's it, simples as that.

Let's look an example:

We have a book model with id, author, title, isbn and publication year.

and We have a book repository interface that extends JpaSpecificationExecutor

The JpaSpecificationExecutor provides two methods:

Now to build our query, We can define the class that implements the Specification interface.

With this static method booksByAuthor, we can use this specification to filter for all books that have an author in common. Let's see how simple it is below:

One aspect of the specification that makes it more interesting is the fact that we can combine the queries. Let's look an example:

And the specification class would look like this:

That's it. Thank you very much for reading this content. I usually bring content with a more hands-on approach and if something wasn't so clear, feel free to comment and suggest improvements.

If you want to know more about this content, I recommend the official documentation:
JPA Specifications