Servlet-ServletContextListener

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package javax.servlet;

import java.util.EventListener;

/**
 * Interface for receiving notification events about ServletContext

 * lifecycle changes.

 这个接口，可以接收到通知事件，这些通知事件是关于ServletContext的生命周期的变化的事件。

 *
 * <p>In order to receive these notification events, the implementation
 * class must be either declared in the deployment descriptor of the web
 * application, annotated with {@link javax.servlet.annotation.WebListener},
 * or registered via one of the addListener methods defined on

 * {@link ServletContext}.

为了接收到这些通知事件，这个实现类必须，要么在Web Application的部署描述中声明（web.xml就是这个部署描述），

要么通过WebListener注解进行注解，或者通过ServletContext的addListener进行注册。

 *
 * <p>Implementations of this interface are invoked at their
 * {@link #contextInitialized} method in the order in which they have been
 * declared, and at their {@link #contextDestroyed} method in reverse

 * order.

这个接口的实现（类）会按照它们声明的顺序依次被调用，在contextInitialized(环境初始化/上下文初始化)，

并且会在contextDestroyed(环境毁坏/上下文毁坏)的时间按照它们声明的顺序的逆序被调用。

 *
 * @see ServletContextEvent
 *
 * @since Servlet 2.3
 */
public interface ServletContextListener extends EventListener {

    /**
     * Receives notification that the web application initialization

     * process is starting.

       web application初始化过程正在开始的时候会接收到通知

     *
     * <p>All ServletContextListeners are notified of context
     * initialization before any filters or servlets in the web

     * application are initialized.

      所有的ServletContextListeners(Servlet环境监听器)会优先得到context(环境/上下文)的初始化通知，

接收context(环境/上下文)的初始化的事件通知，要早于过web应用中的过滤器或者Servlet的初始化的通知。

     *
     * @param sce the ServletContextEvent containing the ServletContext

     * that is being initialized

      这个方法的入参是ServletContextEvent类型的，这个类里面包括一个正在被初始化的ServletContext（Servlet环境/Servlet上下文）。

     */
    public void contextInitialized(ServletContextEvent sce);

    /**
     * Receives notification that the ServletContext is about to be

     * shut down.

   接收通知，这个通知是ServletContext将要被关闭的通知。

     *
     * <p>All servlets and filters will have been destroyed before any

     * ServletContextListeners are notified of context

    所有的servlet和过滤器将会被毁掉，在任何ServeContextListeners(Servlet环境/上下文监听器)被通知之前。

     * destruction.
     *
     * @param sce the ServletContextEvent containing the ServletContext

     * that is being destroyed

      这个方法的入参是ServletContextEvent，它里面包含了那个正在将要被销毁的ServletContext(Servlet环境/上下文)

     */
    public void contextDestroyed(ServletContextEvent sce);
}