How is a composite primary key created in Hibernate?

In Hibernate, a composite primary key is created using the @Embeddable annotation for the class describing the key, and @EmbeddedId in the entity.

Example:

@Embeddable
public class OrderId implements Serializable {
    private Long orderId;
    private Long productId;

    // constructors, getters, setters, equals, and hashCode
}

@Entity
public class Order {
    @EmbeddedId
    private OrderId id;

    private int quantity;

    // other fields, getters, setters
}

Thus, the class with the composite key must be serializable and override equals and hashCode. The entity uses a field annotated with @EmbeddedId.