/** Implementations of this interface receive notifications of
	** changes to the attribute list on the servlet context of a web application.
	* To receive notification events, the implementation class
	* must be configured in the deployment descriptor for the web application.
	* @see ServletContextAttributeEvent
	 * @since	v 2.3
	*/
//实现这个接口会收到web 应用中的servlet context属性链修改的通知
public interface ServletContextAttributeListener extends EventListener {
	/** Notification that a new attribute was added to the servlet context. Called after the attribute is added.*/
	//一个属性被添加给servlet context之前会通知
public void attributeAdded(ServletContextAttributeEvent scab);
	/** Notification that an existing attribute has been removed from the servlet context. Called after the attribute is removed.*/
	//属性被删除之后通知
public void attributeRemoved(ServletContextAttributeEvent scab);
	/** Notification that an attribute on the servlet context has been replaced. Called after the attribute is replaced. */
	//属性被替换后通知
public void attributeReplaced(ServletContextAttributeEvent scab);
}