java web 监听器例子_java web Listener的简单使用案例

电玩女神 2022-11-03 00:58 141阅读 0赞

1 packagetest\_servlet\_package;2 importjava.io.FileOutputStream;3 importjava.io.PrintWriter;4 importjavax.servlet.ServletContext;5 importjavax.servlet.ServletContextEvent;6 importjavax.servlet.ServletContextListener;7 importjavax.servlet.http.HttpSessionActivationListener;8 importjavax.servlet.http.HttpSessionAttributeListener;9 importjavax.servlet.http.HttpSessionBindingEvent;10 importjavax.servlet.http.HttpSessionEvent;11 importjavax.servlet.http.HttpSessionListener;12 public class MySessionListener implementsHttpSessionActivationListener,HttpSessionAttributeListener,HttpSessionListener,ServletContextListener\{13 ServletContext context = null;14 int users = 0;15 public voidsessionWillPassivate(HttpSessionEvent arg0) \{16 //监听Http会话的passivate情况

17 print("sessionWillPassivate("+arg0.getSession().getId()+")");18 \}19 public voidsessionDidActivate(HttpSessionEvent arg0) \{20 //监听Http会话的active情况

21 print("sessionDidActivate("+arg0.getSession().getId()+")");22 \}23 public voidattributeAdded(HttpSessionBindingEvent arg0) \{24 //监听Http会话中的属性添加

25 print("attributeAdded('"+arg0.getSession().getId()+"','"+arg0.getName()+"','"+arg0.getValue()+"')");26 \}27 public voidattributeRemoved(HttpSessionBindingEvent arg0) \{28 //监听Http会话中的属性删除

29 print("attributeRemoved('"+arg0.getSession().getId()+"','"+arg0.getName()+"','"+arg0.getValue()+"')");30 \}31 public voidattributeReplaced(HttpSessionBindingEvent arg0) \{32 //监听Http会话中的属性更改操作

33 print("attributeReplaced('"+arg0.getSession().getId()+"','"+arg0.getName()+"','"+arg0.getValue()+"')");34 \}35 public voidsessionCreated(HttpSessionEvent arg0) \{36 //Http会话的创建监听

37 users++; //创建一个会话，把users变量加1

38 print("sessionCreated('"+arg0.getSession().getId()+"'),目前拥有"+users+"个用户");39 context.setAttribute("users",new Integer(users)); //把会话数设置到ServletContext的属性users中

40 \}41 public voidsessionDestroyed(HttpSessionEvent arg0) \{42 //Http会话的释放监听

43 users--;//释放一个会话，把users变量减1

44 print("sessionDestroyed('"+arg0.getSession().getId()+"'),目前拥有"+users+"个用户");45 context.setAttribute("users",new Integer(users)); //把会话数设置到ServletContext的属性users中

46 \}47 public voidcontextInitialized(ServletContextEvent arg0) \{48 //该方法实现了ServletContextListener接口定义的方法，对ServletContext进行初始化

49 this.context = arg0.getServletContext();//初始化ServletContext对象

50 print("ServletContext初始化......");//打印出该方法的操作信息

51 \}52 public voidcontextDestroyed(ServletContextEvent arg0) \{53 //监听Servlet上下文被释放

54 this.context = null; //释放ServletContext对象

55 print("ServletContext被释放......");//打印出该方法的操作信息

56 \}57 private voidprint(String message)\{58 //调用该方法在txt文件中打印出message字符串信息

59 PrintWriter out = null;60 try\{61 out = new PrintWriter(new FileOutputStream("d:\\\\output.txt",true));62 out.println(new java.util.Date()+" SessionListener: "+message);63 out.close();64 \}catch(Exception e)\{65 e.printStackTrace();66 \}67 \}68 /\*

69 (1)该程序实现了HttpSessionListener接口类中的两个方法：70 ● sessionCreated(HttpSessionEvent arg0)方法进行Http会话创建的监听，如果Http会话被创建将调用该方法。71 ● sessionDestroyed(HttpSessionEvent arg0)方法对Http会话销毁进行监听，如果某个Http会话被释放将调用该方法。72 (2)实现HttpSessionActivationListener接口类中的如下两个方法：73 ● sessionDidActivate(HttpSessionEvent arg0)方法对Http会话处于active情况进行监听。74 ● sessionWillPassivate(HttpSessionEvent arg0)方法对Http会话处于passivate情况进行监听。75 (3)实现HttpSessionAttributeListener接口类中的如下3种方法：76 ● attributeAdded(HttpSessionBindingEvent arg0)方法对Http会话中属性添加进行监听。77 ● attributeReplaced(HttpSessionBindingEvent arg0)方法对Http会话中属性修改进行监听。78 ● attributeRemoved(HttpSessionBindingEvent arg0)方法对Http会话中属性删除进行监听。79 (4)另外，该程序中还实现了ServletContextListener接口类，该类的实现方法已经在12.2.1小节中有所介绍。80 同样需要在web.xml配置文件进行该监听器的声明，该监听器实现了在线会话人数的统计，81 当一个会话创建时，users变量将加1；当销毁一个会话对象的时候，users变量将减1。82 \*/

84 \}