ServletContextListener接口的源码
package javax.servlet; import java.util.EventListener; /** * Implementations of this interface receive notifications about * changes to the servlet context of the web application they are * part of. * To receive notification events, the implementation class * must be configured in the deployment descriptor for the web * application. * @see ServletContextEvent * @since v 2.3 */ public interface ServletContextListener extends EventListener { /** ** Notification that the web application initialization ** process is starting. ** All ServletContextListeners are notified of context ** initialization before any filter or servlet in the web ** application is initialized. */ public void contextInitialized ( ServletContextEvent sce ); /** ** Notification that the servlet context is about to be shut down. ** All servlets and filters have been destroy()ed before any ** ServletContextListeners are notified of context ** destruction. */ public void contextDestroyed ( ServletContextEvent sce ); } 此接口被EventListener标记，用来接收web应用中servlet 上下文变化的通知，同时，为了接收通知事件。该 具体实现类必须在web.xml中配置（部署描述符）。其中设计了两个方法：
//通知web应用的初始化处理开始，所有的ServletContextListeners在filter or servlet在（web应用）初始化之前都会被接收到上下文初始化的信息。
public void contextInitialized ( ServletContextEvent sce );
//在上下文中的销毁中，所有的filter or servlet在销毁之间ServletContextListeners都会被提前通知。
public void contextDestroyed ( ServletContextEvent sce );
其中的实现类有：
同时该接口引入了ServletContextEvent事件类：
ServletContextEvent：这是关于Web应用程序的servlet上下文更改的通知的事件类。
package javax.servlet; /** * This is the event class for notifications about changes to * the servlet context of a web application. * @see ServletContextListener * @since v 2.3 */ public class ServletContextEvent extends java.util.EventObject { /** 从给定的上下文中构建一个ServletContextEvent对象 * * @param source - the ServletContext that is sending the event. */ public ServletContextEvent(ServletContext source) { super(source); } /** * 返回一个Servlet上下对象 * * @return the ServletContext that sent the event. */ public ServletContext getServletContext () { return (ServletContext) super.getSource(); } } 其中有EventObject和ServletContext。对于EventObject没啥特别的就是jdk工具类提供的一个事件对象，获取对象只能通过getSource返回一个Object。
ServletContextEvent也使用相同的手段，只能通过传入一个ServletContext构建一个对象，并返回ServletContext。
package java.util; /** * <p> * The root class from which all event state objects shall be derived. * <p> * All Events are constructed with a reference to the object, the "source", * that is logically deemed to be the object upon which the Event in question * initially occurred upon. * * @since JDK1.1 */ public class EventObject implements java.io.Serializable { private static final long serialVersionUID = 5516075349620653480L; /** * The object on which the Event initially occurred. */ protected transient Object source; /** * Constructs a prototypical Event. * * @param source The object on which the Event initially occurred. * @exception IllegalArgumentException if source is null. */ public EventObject(Object source) { if (source == null) throw new IllegalArgumentException("null source"); this.source = source; } /** * The object on which the Event initially occurred. * * @return The object on which the Event initially occurred. */ public Object getSource() { return source; } /** * Returns a String representation of this EventObject. * * @return A a String representation of this EventObject. */ public String toString() { return getClass().getName() + "[source=" + source + "]"; } } 对于ServletContext只是定义了一系列Servlet与Servlet容器通信的方法，例如获取一个文件的MIME的类型，分配一个请求或者写日志文件。在java虚拟机中一个应用只有一个上下文ServletContext
