servlet監聽器
在WEB應用中響應特定對象的特定事件
好處:更方便的控制application,session,request對象的發生的特定事件
可以集中處理特定的事件
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HttpSession監聽器接口
1 HttpSessionListener(需要配web.xml)
2 HttpSessionAttributeListener(需要配web.xml)
3 HttpSessionBindingListener
4 HttpSessionActivationListener(需要配web.xml)
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HttpSessionListener
1 sessionCreated()//當session對象產生的時候調用的方法
2 sessionDestroyed()//當session對象消滅的時候調用的方法
web.xml配置
<listener>
<listener-class>webbook.chapter14.CounterListener(對應的實現類)
</listener-class>
</listener>
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HttpSessionAttributeListener
1 attributeAdded()//添加時調用
2 attributeReplaced()//替換時調用
3 attributeRemoved()//刪除時調用
產生事件的代碼
session.setAttribute("username","wangwu");
session.setAttribute("username","lisi");
session.removeAttribute("username");
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HttpSessionBindingListener
1 valueBound();
2 vaoueUnbound();
調用機制
如果一個類實現了HttpSessionBindingListener接口,則當這個類的對象通過session.setAttribute()被綁定到Session對象中時,
則該對象的valueBound()方法被自動調用,當這個對象從Session中刪除時(調用session.invalidate()和session.removeAtrribute()
方法,或Session對象過期)valueUnbound()方法將被自動調用.
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HttpSessionActivationListener
1 sessionDidActivate();
2 sessionWillPassivate();
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例子:
1 建立CounterListener處理類
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class CounterListener implements HttpSessionListener {
private static long onlineNumber=0;
public void sessionCreated(HttpSessionEvent se) {
onlineNumber++;
}
public void sessionDestroyed(HttpSessionEvent se) {
onlineNumber--;
}
public static long getOnlineNumber(){
return onlineNumber;
}
}
2 配置web.xml
<listener>
<listener-class>com.tags.CounterListener</listener-class>
</listener>
3 JSP頁面
<%@page import="com.tags.CounterListener;"%>
<body>
當前的在線人數：<%=CounterListener.getOnlineNumber() %> <br>
</body>
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ServletContext監聽器接口
ServletContextListener
1 contextInitialized()
2 contextDestroyed()
調用機制
當在web應用中部署了實現該接口的實現類后,在WEB容器加載WEB應用時(如:啟動服務器)就會自動調用contextInitialized()方法,
而當WEB容器銷毀WEB應用時(如:關閉服務器),會自動調用contextDestroyed()方法.
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ServletContextAttributeListener
1 attributeAdded()
2 attributeReplaced()
3 attributeRemoved()
觸發事件的代碼
context.setAttribute("counter",new Integer(0));
context.setAttribute("counter",new Integer(100));
context.removeAttribute("counter");
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HttpServletRequest監聽器
ServletRequestListener
1 requestInitialized();
2 requestDestroyed()
調用機制
與ServletContextListener接口類似,在web應用中部署實現該接口的實現類扣,在HttpServletRequest對象(JSP中的request對象)建立
或者被銷毀時,由web容器自動調用requestInitialized()或者requestDestroyed()方法.
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ServletRequestAttributeListener
1 attributeAdded();
2 attributeReplaced();
3 attributeRemoved();
觸發事件的代碼
request.setAttribute("username","lisi");
request.setAttribute("username","wangwu");
request.removeAttribute("username");
******************************************************************
public class ListenerOnline implements HttpSessionLinstener,ServletContext{
private application;
public void sessionCreated(HttpSessionEvent event){
Integer n=(Integer)application.getAttrabute("z",1000);
application.setAttrabute("z",n.IntValue()+1);
}
public void sessionDestroyed(HttpSessionEvent event){
}
public void contextInitialized(ServletContextEvent event){
application=event.getServletContext();
application.setAttrabute("z",1000);
}
public void contextDestroyed(ServletContextEvent event){
}
}
<listener>
<listener-class>com.tags.ListenerOnline</listener-class>
</listener>
<meta http-equiv="refresh" content="3"/>
posted on 2009-11-29 22:47
junly 閱讀(330)
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