listener

来源：互联网发布：怎么在电脑上切换网络编辑：程序博客网时间：2024/05/01 13:00

java_ee_sdk-5-javadocs\docs\api\index.html中的javax.servlet.http下有
ServletContextListener：           session的创建和销毁
HttpSessionAttributeListener：session的attribute属性改变
以下示例参考drp项目
一、ServletContextListener示例：
1、java代码中：
public class InitListener implements ServletContextListener {
   public void contextDestroyed(ServletContextEvent sce) {
   }
   public void contextInitialized(ServletContextEvent sce) {
       System.out.println("InitListener.init()");
       System.out.println("创建系统的BeanFactory...");
       //将抽象工厂放到ServletContext中
       BeanFactory beanFactory = BeanFactory.getInstance();
       sce.getServletContext().setAttribute("beanFactory", beanFactory);
       //加入常量
       sce.getServletContext().setAttribute("add", Constants.ADD);
       sce.getServletContext().setAttribute("del", Constants.DEL);
       sce.getServletContext().setAttribute("modify", Constants.MODIFY);
       sce.getServletContext().setAttribute("showAdd", Constants.SHOW_ADD);
       sce.getServletContext().setAttribute("audit", Constants.AUDIT);
   }
}
2、web.xml中：
<listener>
   <listener-class>com.bjpowernode.drp.util.listener.InitListener</listener-class>
</listener>

二、HttpSessionAttributeListener示例：用来显示当前用户在线数,不过有半小时的误差，因为session关闭后tomcat服务器默认半小时后才会发现。
1、java代码中：
public class TestHttpSessionAttributeListener implements HttpSessionAttributeListener {
   public void attributeAdded(HttpSessionBindingEvent se) {
       System.out.println("TestHttpSessionAttributeListener-->>>attributeAdded()");
       System.out.println("name=====" + se.getName());
       System.out.println("value=====" + se.getValue());
       if ("user_info".equals(se.getName())) {
           Integer count = (Integer)se.getSession().getServletContext().getAttribute("count");
           if (count == null) {
               count = 1;
           }else {
               count++;
           }
           se.getSession().getServletContext().setAttribute("count", count);
       }
   }
   public void attributeRemoved(HttpSessionBindingEvent se) {
       System.out.println("TestHttpSessionAttributeListener-->>>attributeRemoved()");
   }
   public void attributeReplaced(HttpSessionBindingEvent se) {
       System.out.println("TestHttpSessionAttributeListener-->>>attributeReplaced()");
   }
}
2、web.xml中：
<listener>
   <listener-class>com.bjpowernode.drp.util.listener.TestHttpSessionAttributeListener</listener-class>
</listener>