Listener
1、概念
注册监听:将事件、事件源、监听器绑定在一起。 当事件源上发生某个事件后,执行监听器代码
ServletContextListener 接口,它能够监听 ServletContext 对象的生命周期,实际上就是监听 Web 应用的生命周期。
2、代码实现
package com.beiyou.listener;
import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
public class Listener1 implements ServletContextListener {
@Override
public void contextInitialized(ServletContextEvent servletContextEvent) {
//ServletContext对象创建后会调用该方法
System.out.println("Listener1 -> contextInitialized"); //扩展内容明天讲 ServletContext sct=sce.getServletContext();
sct.setAttribute("mysql", "127.0.0.1");
}
@Override
public void contextDestroyed(ServletContextEvent servletContextEvent) {
//ServletContext对象被销毁之前会调用该方法
System.out.println("Listener1 -> contextDestroyed");
}
}
<listener>
<listener-class>com.beiyou.listener.Listener1</listener-class>
</listener>
<listener>
<listener-class>com.beiyou.listener.Listener2</listener-class>
</listener>
3. 使用注解
@WebListener
4.扩展
public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException, ServletException {
ServletConfig servletConfig = getServletConfig();
Object mysql = servletConfig.getServletContext().getAttribute("mysql");
request.getRequestDispatcher("login.jsp").forward(request, response);
}