BookService.java

package com.example.demo;

import org.springframework.stereotype.Service;

@Service
public class BookService {
    public Book getBookById(String id){
        try{
            // simulate slow retrieval from DB
            Thread.sleep(2000);
        }catch(Exception e){
            e.printStackTrace();
        }
        return new Book(id, "Book " + id);
    }
}