https://www.heckjj.com/index.php zh-cn https://www.heckjj.com/post// Heck <@hecks.tk> Sun, 30 Mar 2014 09:03:23 +0000 https://www.heckjj.com/post// 因此，在通知上下文(context)初始化和销毁的时候，ServletContextListner非常有用。

import javax.servlet.ServletContextListener; import javax.servlet.ServletContextEvent; import javax.servlet.*; public class MyListener implements ServletContextListener { private ServletContext context = null; public void contextDestroyed(ServletContextEvent event){   //Output a simple message to the server's console   System.out.println("The Simple Web App. Has Been Removed");   this.context = null; } // 这个方法在Web应用服务做好接受请求的时候被调用。 public void contextInitialized(ServletContextEvent event){   this.context = event.getServletContext();   //Output a simple message to the server's console   System.out.println("The Simple Web App. Is Ready"); } }

<web-app> <listener>   <listener-class>    com.listeners.MyContextListener   </listener-class> </listener> <servlet/> <servlet-mapping/> </web-app>
ServletContextListener接口有两方需要实现的方法:
contextInitialized()和contextDestroyed();
Listener,译为监听者.顾名思义,它会监听Servlet容器(实际上就是中间件启动和销毁时执行的方法),当应用开始的时候它会调用contextInitialized()方法;
当应用关闭的时候,它同样会调用contextDestroyed()方法.
我们可以利用这个特性初始化一些信息,当然我们也可以利用Servlet类init()方法,并在配置文件中让它启动应用的时候
就执行,并且在关闭的时候执行destroy()方法.但是继承此接口应该更符合容器的应用.
举个简单的例子:在一些论坛,社区及聊天室当中,删除在线的超时用户就可以利用这个接口来实现.
可以利用JAVA的TimerTask及Timer类来实现每隔一定的时间进行自动检测.

实例代码如下:
UserOnlineTimerTask.java
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package tk.hecks.servlet; import java.util.TimerTask; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; public class UserOnlineTimerTask extends TimerTask { Log log = LogFactory.getLog(UserOnlineTimerTask.class); public void run() { // 删除超时在线用户 log.info("删除在线的超时用户...."); } }
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SysListener.java
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package tk.hecks.servlet; import java.io.IOException; import java.util.Timer; import javax.servlet.ServletContextEvent; import javax.servlet.ServletContextListener; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServlet; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; public class SysListener extends HttpServlet implements ServletContextListener { Log log = LogFactory.getLog(SysListener.class); Timer timer = new Timer(); public void service(ServletRequest request, ServletResponse response) throws ServletException, IOException { // } public void contextInitialized(ServletContextEvent sce) { log.info("initial context...."); timer.schedule(new UserOnlineTimerTask(), 0, 10000); } public void contextDestroyed(ServletContextEvent sce) { log.info("destory context...."); timer.cancel(); } }
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如果你没有使用log4j的话,你可以把log.info()改为System.out.println()会得到同样的结果.
Tags - servlet , timer , class , log4j , webserver ]]> https://www.heckjj.com/post//#blogcomment <user@domain.com> Thu, 01 Jan 1970 00:00:00 +0000 https://www.heckjj.com/post//#blogcomment