（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)
        {

        }

}