首先需要時web專案

監聽類，實現介面HttpSessionListener，由於這個struts2專案，所有有一些其他的配置，為了較為容易的看到效果，這個對session設定了時效為1分鐘，可以寫程式碼，也可以直接在myeclipse中寫東西

import java.text.SimpleDateFormat;
import java.util.Date;

import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class SessionListenerTest implements HttpSessionListener {
	int i;

	SimpleDateFormat sdf=new SimpleDateFormat("HH:mm:ss");
	@Override
	public void sessionCreated(HttpSessionEvent arg0) {
		i++;
		// TODO Auto-generated method stub
		System.out.println("session被建立了-來自session監聽器      "+sdf.format(new Date())+"目前線上人數為:"+i);

	}

	@Override
	public void sessionDestroyed(HttpSessionEvent arg0) {
		i--;
		// TODO Auto-generated method stub
		System.out.println("session被銷燬了-來自session監聽器      "+sdf.format(new Date())+"目前線上人數為:"+i);
	}
	
	

}
 

web.xml的配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee   http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">
 <filter>
  <filter-name>struts2filter</filter-name>
  <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>
 </filter>
 <filter-mapping>
  <filter-name>struts2filter</filter-name>
  <url-pattern>/*</url-pattern>
 </filter-mapping>
 <listener>
  <description>用於監聽session的建立和銷燬</description>
  <listener-class>filter.action.SessionListenerTest</listener-class>
 </listener>
 <session-config>
  <session-timeout>1</session-timeout>
 </session-config>
 <welcome-file-list>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
 <login-config>
  <auth-method>BASIC</auth-method>
 </login-config>
</web-app>