BookstoreService.java

package com.bookstore.service;

import com.bookstore.projection.AuthorInfo;
import com.bookstore.repository.AuthorRepository;
import java.util.List;
import org.springframework.data.domain.Page;
import org.springframework.data.domain.PageImpl;
import org.springframework.data.domain.PageRequest;
import org.springframework.data.domain.Pageable;
import org.springframework.data.domain.Sort;
import org.springframework.stereotype.Service;

@Service
public class BookstoreService {

    private final AuthorRepository authorRepository;

    public BookstoreService(AuthorRepository authorRepository) {
        this.authorRepository = authorRepository;
    }

    public Page<AuthorInfo> fetchNextPage(int page, int size) {
        Pageable pageable = PageRequest.of(page, size, new Sort(Sort.Direction.ASC, "age"));

        List<AuthorInfo> authors = authorRepository.fetchAll(pageable);
        Page<AuthorInfo> pageOfAuthors = new PageImpl(authors, pageable,
                authors.isEmpty() ? 0 : authors.get(0).getTotal());

        return pageOfAuthors;
    }
}