package com.springmvc.controller;
...
import org.springframework.web.bind.annotation.RequestParam;

@Controller
@RequestMapping("/books")
public class BookController {
    @Autowired
    private BookService bookService;
    ...
    @GetMapping("/book") ➊
    public String requestBookById(@RequestParam("id") String bookId, Model model) { ➋
        Book bookById = bookService.getBookById(bookId);
        model.addAttribute("book", bookById);
        return "book";
    }
}