BookController.java

package com.example.demo;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

@RestController
public class BookController {

    @Autowired
    BookService bookService;

    @Autowired
    CacheStore<Book> bookCache;

    @GetMapping("/")
    public String index(){
        return "OK";
    }

    @GetMapping(value = "/book/{id}")
    public Book getBook(@PathVariable String id){
        // get book from cache
        Book cached = bookCache.get(id);
        if(cached != null){
            return cached;
        }
        // get book from service
        Book book = bookService.getBookById(id);
        // add book to cache
        bookCache.add(id, book);
        return book;
    }
}