@@ -1,9 +1,113 @@
 package com.ll.nbe342team8.domain.book.book.service;
 
+import com.ll.nbe342team8.domain.book.book.dto.BookPatchRequestDto;
+import com.ll.nbe342team8.domain.book.book.dto.BookResponseDto;
+import com.ll.nbe342team8.domain.book.book.dto.ExternalBookDto;
+import com.ll.nbe342team8.domain.book.book.entity.Book;
+import com.ll.nbe342team8.domain.book.book.repository.BookRepository;
+import com.ll.nbe342team8.domain.book.book.type.SortType;
+import jakarta.persistence.EntityNotFoundException;
 import lombok.RequiredArgsConstructor;
+import org.springframework.data.domain.Page;
+import org.springframework.data.domain.PageRequest;
+import org.springframework.data.domain.Pageable;
+import org.springframework.data.domain.Sort;
 import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.time.LocalDate;
+import java.util.ArrayList;
+import java.util.List;
 
 @Service
 @RequiredArgsConstructor
 public class BookService {
-}
+
+    private final ExternalBookApiService externalBookApiService;
+    private final BookRepository bookRepository;
+
+    public Page<Book> getAllBooks(int page, int pageSize, SortType sortType) {
+        List<Sort.Order> sorts = new ArrayList<>();
+        sorts.add(sortType.getOrder());
+
+        Pageable pageable = PageRequest.of(page, pageSize, Sort.by(sorts));
+        return bookRepository.findAll(pageable);
+    }
+
+    public Book getBookById(Long id) {
+        if (id == null) {
+            throw new IllegalArgumentException("ID 값이 null입니다.");
+        }
+        return bookRepository.findById(id)
+                .orElseThrow(() -> new IllegalArgumentException("해당 ID(" + id + ")의 책을 찾을 수 없습니다."));
+    }
+
+    public long count() {
+        return bookRepository.count();
+    }
+
+    public Book create(Book book) {
+        return bookRepository.save(book);
+    }
+
+    public Book createReview(Book book, float rating) {
+        book.createReview(rating);
+        return bookRepository.save(book);
+    }
+
+    public Book deleteReview(Book book, float rating) {
+        book.deleteReview(rating);
+        return bookRepository.save(book);
+    }
+
+    public Page<Book> searchBooks(int page, int pageSize, SortType sortType, String title) {
+        List<Sort.Order> sorts = new ArrayList<>();
+        sorts.add(sortType.getOrder());
+
+        Pageable pageable = PageRequest.of(page, pageSize, Sort.by(sorts));
+        return bookRepository.findBooksByTitleContaining(title, pageable);
+    }
+
+    // 도서 추가
+    @Transactional
+    public Book addBook(String isbn13) {
+
+        if (bookRepository.existsByIsbn13(isbn13)) {
+            throw new IllegalArgumentException("이미 등록된 도서입니다.");
+        }
+
+        ExternalBookDto externalBookDto = externalBookApiService.searchBook(isbn13);
+
+        Book book = mapToEntity(externalBookDto);
+
+        return bookRepository.save(book);
+    }
+
+    private Book mapToEntity(ExternalBookDto dto) {
+        return Book.builder()
+                .title(dto.getTitle())
+                .author(dto.getAuthor())
+                .isbn(dto.getIsbn())
+                .isbn13(dto.getIsbn13())
+                .pubDate(LocalDate.parse(dto.getPubDate()))
+                .priceStandard(dto.getPriceStandard())
+                .pricesSales(dto.getPriceSales())
+                .toc(dto.getToc())
+                .coverImage(dto.getCover())
+                .description(dto.getDescription())
+                .descriptionImage(dto.getDescriptionImage())
+                .categoryId(dto.getCategoryId())
+                .build();
+    }
+
+    // 도서 정보 수정
+    @Transactional
+    public BookResponseDto updateBookPart(Long bookId, BookPatchRequestDto requestDto) {
+        Book book = bookRepository.findById(bookId)
+                .orElseThrow(() -> new EntityNotFoundException("책을 찾을 수 없습니다."));
+
+        book.update(requestDto); // DTO 에서 null 이 아닌 값만 업데이트
+
+        return BookResponseDto.from(book);
+    }
+}
\ No newline at end of file

리뷰: 애초에 입력 값에서 id가 notnull 임을 validate 하는게 맞지 않을까요?
기본적인 validation 을 service 레이어에서 수행하게 하지 말아주세요.