//这是一个事件类用来通知一个web 应用的servlet 上下文的改变
public class ServletContextEvent extends java.util.EventObject { 

	/** Construct a ServletContextEvent from the given context.
	 *
	 * @param source - the ServletContext that is sending the event.
	 */
    public ServletContextEvent(ServletContext source) {
	super(source);
    }

	/**
	 * Return the ServletContext that changed.
	 *
	 * @return the ServletContext that sent the event.
	 */
    public ServletContext getServletContext () {
	return (ServletContext) super.getSource();
    }

}

public class ServletContextAttributeEvent extends ServletContextEvent {
	private String name;
	private Object value;

	/** Construct a ServletContextAttributeEvent from the given context for the
	** given attribute name and attribute value.
	*/
	//构造一个servlet上下文属性事件
	public ServletContextAttributeEvent(ServletContext source, String name, Object value) {
	    super(source);
	    this.name = name;
	    this.value = value;
	}

	/**
	* Return the name of the attribute that changed on the ServletContext.
	*
	*/

	public String getName() {
		return this.name;
	}

	/**
	* Returns the value of the attribute that has been added, removed, or replaced.
	* If the attribute was added, this is the value of the attribute. If the attribute was
	* removed, this is the value of the removed attribute. If the attribute was replaced, this
	* is the old value of the attribute.
	*
	*/

	public Object getValue() {
	    return this.value;
	}
}