Getting data from REST

@RestController
public class LibraryController {

    private List<Book> books = new ArrayList<>();

    // 1
    @GetMapping(path = "/books/{id}")
    public Book getBookById(@PathVariable int id) {
        return books.get(id - 1);
    }

    // 2
    @GetMapping(path = "/books")
    public Book getBook() {
        return books.get(0);
    }

    // 3
    @GetMapping(path = "/books/{name}")
    public Book getBookByName(@PathVariable String name) {
        Book book;
        for (Book value : books) {
            book = value;
            if (book.getName().equals(name)) return book;
        }
        return null;
    }

}

@RestController
class LibraryController {
    private val books: List<Book> = ArrayList()

    // 1
    @GetMapping("/books/{id}")
    fun getBookById(@PathVariable id: Int): Book {
        return books[id - 1]
    }

    // 2
    @GetMapping("/books")
    fun getBook(): Book {
        return books[0]
    }

    // 3
    @GetMapping("/books/{name}")
    fun getBookByName(@PathVariable name: String?): Book? {
        var book: Book
        for (value in books) {
            book = value
            if (book.getName().equals(name)) return book
        }
        return null
    }
}