（1）在一个类中编写普通的virtual方法
（2）在派生类中实现接口中的方法时，也可以标记为virtual
public interface IServer
{
/// <summary>
/// 响应GET方法
/// </summary>
/// <param name="request">Http请求</param>
void OnGet(HttpRequest request, HttpResponse response);
/// <summary>
/// 响应Post方法
/// </summary>
/// <param name="request">Http请求</param>
void OnPost(HttpRequest request, HttpResponse response);
/// <summary>
/// 响应默认请求
/// </summary>
/// <param name="request">Http请求</param>
void OnDefault(HttpRequest request, HttpResponse response);
}
public class HttpServer : IServer
{
/// <summary>
/// 响应Post请求（virtual作用：在子类中可以被重写，从而提现个性化；在此处编写公共逻辑，从而体现共性）
/// </summary>
/// <param name="request"></param>
public virtual void OnPost(HttpRequest request, HttpResponse response)
{
}
}