package com.springmvc.controller;
...
import com.springmvc.exception.CategoryException;

@Controller
@RequestMapping("/books")
public class BookController {
    ...

    @GetMapping("/{category}")
    public String requestBooksByCategory(@PathVariable("category") String bookCategory, Model model) {
        List<Book> booksByCategory = bookService.getBookListByCategory(bookCategory);

        if (booksByCategory == null || booksByCategory.isEmpty()) {
            throw new CategoryException();
        }
        model.addAttribute("bookList", booksByCategory);
        return "books";
    }
    ...
}