java-tutorials/spring-rest-http/src/main/java/com/baeldung/service/CustomerService.java

package com.baeldung.service;

import com.baeldung.model.Customer;

import java.util.Optional;

public interface CustomerService {

    Customer createCustomer(Customer customer);

    Optional<Customer> findCustomer(String id);

    void updateCustomer(Customer customer);
}