package com.springmvc.repository;
...
@Repository
public class BookRepositoryImpl implements BookRepository {
    ...
    public Set<Book> getBookListByFilter(Map<String, List<String>> filter) {
    ...
    }

    public Book getBookById(String bookId) {
        Book bookInfo = null;
        for (int i = 0; i < listOfBooks.size(); i++) {
            Book book = listOfBooks.get(i); 
            if (book != null && book.getBookId() != null && book.getBookId().equals(bookId)) {
                bookInfo = book;
                break;
            }
        }
        if (bookInfo == null) 
            throw new IllegalArgumentException("도서 ID가 " + bookId + "인 해당 도서를 찾을 수 없습니다.");
            return bookInfo;
    }
}