How to implement data search using Spring Data JPA based on specified conditions?

In Spring Data JPA, there are several approaches to search for data based on specified conditions:

1. Repository methods with named queries — create methods in the repository interface with names reflecting the search conditions, for example:

public interface UserRepository extends JpaRepository<User, Long> {
    List<User> findByLastNameAndAge(String lastName, int age);
}

2. @Query with JPQL or native SQL — write the query manually:

@Query("SELECT u FROM User u WHERE u.lastName = :lastName AND u.age = :age")
List<User> findUsers(@Param("lastName") String lastName, @Param("age") int age);

3. Specification API — for dynamic construction of conditions:

public class UserSpecification implements Specification<User> {
    private String lastName;
    private Integer age;

    public UserSpecification(String lastName, Integer age) {
        this.lastName = lastName;
        this.age = age;
    }

    @Override
    public Predicate toPredicate(Root<User> root, CriteriaQuery<?> query, CriteriaBuilder cb) {
        List<Predicate> predicates = new ArrayList<>();
        if (lastName != null) {
            predicates.add(cb.equal(root.get("lastName"), lastName));
        }
        if (age != null) {
            predicates.add(cb.equal(root.get("age"), age));
        }
        return cb.and(predicates.toArray(new Predicate[0]));
    }
}

And then use it in the repository:

List<User> users = userRepository.findAll(new UserSpecification("Smith", 30));

Thus, the choice of method depends on the complexity and dynamism of the search conditions.