Hibernate Processor is a standard Java annotation processor which produces the Jakarta Persistence static metamodel, validates queries at compilation time, and implements Jakarta Data repositories.
Jakarta Persistence static metamodel
The static metamodel is a standard part of JPA.
It lets us reference the persistent fields and properties of an entity in a completely typesafe way.
Consider the entity class Order:
@Entity
public class Order {
@Id
@GeneratedValue
Integer id;
@ManyToOne
Customer customer;
@OneToMany
Set<Item> items;
BigDecimal totalCost;
// ...
}Hibernate Processor would generate the static metamodel class Order_, something like this:
// code generated by the annotation processor
@StaticMetamodel(Order.class)
public class Order_ {
public static volatile SingularAttribute<Order, Integer> id;
public static volatile SingularAttribute<Order, Customer> customer;
public static volatile SetAttribute<Order, Item> items;
public static volatile SingularAttribute<Order, BigDecimal> totalCost;
}The static metamodel class allows to write criteria queries like this, without the use of strings:
var builder = entityManager.getCriteriaBuilder();
var query = builder.createQuery(Order.class);
var item = query.from(Order.class).join(Order_.items);
query.where(builder.equal(item.get(Item_.id), 5)).distinct(true);Query validation
Hibernate Processor is able to completely validate HQL, JPQL, and JDQL queries provided via annotations—for example, using a JPA @NamedQuery annotation, a Jakarta Data @Query annotation, or a Hibernate @HQL annotation—and report any errors in the syntax or typing of the query at compilation time.
Hibernate Data Repositories
Hibernate Processor is the thing which provides the implementation of a @Repository interface in our implementation of Jakarta Data, Hibernate Data Repositories.
You write a repository interface like this:
@Transactional
@Repository
public interface Library {
@Find
Optional<Book> byIsbn(String isbn);
@Find
List<Book> byTitle(@Pattern String title);
@Insert
void add(Book book);
@Delete
void delete(String isbn);
@Find
List<Book> allBooks(Sort<Book> bookSort);
@Find
@OrderBy(_Book.ISBN)
List<Book> allBooks();
}Then Hibernate Processor provides an implementation which complies with the semantics defined by the Jakarta Data specification.