为什么要将接口声明为抽象？(Why declare an interface as abstract?)

 destroy()是卸载特定Servlet实例时由Servlet容器调用的生命周期方法。 同样，当有客户请求Servlet时， 容器将调用service() 。 
 
 
 
 我们可以从Servlet中的destroy()方法调用service()方法吗？ 
 
 
 简短的回答： 是的 ，因为service()是一种像其他任何方法一样的方法。 
 
 长答案：你可以，但这没有意义。 service()需要一个请求和一个响应参数，这些参数通常在调用Servlet时由容器提供。 如果你自己打电话给service() ，你将如何提供这些参数？ 做什么的？ 你会在两者上使用null吗？ 两个空参数的service()什么好处？ 
 
 
 
 我们可以在Servlet中的service()方法中调用destroy()方法吗？ 
 
 
 是的 ，您可以再次从service()调用destroy() ，因为它也是其他方法。 虽然仍然很奇怪，但有时这可能是有意义的，因为destroy()会执行你定义的任何逻辑（清理，删除属性等）。 
 
 
 重要提示：请记住，简单地调用destroy()将不会卸载 Servlet实例。 您不管理程序中Servlet的生命周期，Servlet容器就是这样。 

destroy() is a lifecycle method called by the Servlet container when unloading a specific instance of the Servlet. Similarly, the container will call service() when there's a client requesting the Servlet.
 
 
 
Can we call service() method from destroy() method in Servlet?
 
 
Short answer: Yes, as service() is a method like any other.
 
Long answer: You can, but it doesn't make sense. service() requires a request and a response parameters that are usually provided by the container when the Servlet is called. If you are calling service() by yourself, how are you gonna provide those parameters? What for? Are you gonna use null on both? What good is service() for two empty parameters?
 
 
 
Can we call destroy() method from service() method in Servlet?
 
 
Yes, again, you can call destroy() from within the service() as it is also a method like any other. Although still strange, this could make sense sometimes, as destroy() will do whatever logic you have defined (cleanup, remove attributes, etc.).
 
 
IMPORTANT: Just bear in mind that simply calling destroy() won't unload the Servlet instance. You do not manage the lifecycle of Servlets in the program, the Servlet Container does.