首先编写一个模型类[如果还需要其他信息可增加类属性]：
代码:
package com.bupticet.listener;
public class OnlineModel{
  private String userName;
  private String ipAddress;
  private String loadTime;
  private String address;
  /**
   * OnlineModel
   */
  public OnlineModel() {
  }
  public OnlineModel(String name,String ip,
                     String time,String address){
    this.userName = name;
    this.ipAddress = ip;
    this.loadTime = time;
    this.address = address;
  }
  public String getIpAddress() {
    return ipAddress;
  }
  public String getAddress() {
    return address;
  }
  public String getLoadTime() {
    return loadTime;
  }
  public void setUserName(String userName) {
    this.userName = userName;
  }
  public void setIpAddress(String ipAddress) {
    this.ipAddress = ipAddress;
  }
  public void setAddress(String address) {
    this.address = address;
  }
  public void setLoadTime(String loadTime) {
    this.loadTime = loadTime;
  }
  public String getUserName() {
    return userName;
  }
  public String toString(){
    return this.userName+"    "+this.ipAddress+"    "+this.loadTime+"    "+this.address+"\n\n"+"<br>";
  }
}
再写一个session监听类，实现HttpSessionListener接口：
代码:
package com.bupticet.listener;
import javax.servlet.*;
import javax.servlet.http.*;
import java.util.*;
public class OnlineList implements HttpSessionAttributeListener{
	private static List list=new ArrayList();
	public void attributeAdded(HttpSessionBindingEvent se){
		if("online".equals(se.getName()))	{
			list.add((OnlineModel)(se.getValue()));
		}
	}
	public void attributeRemoved(HttpSessionBindingEvent se){
		if("online".equals(se.getName())){
			list.remove((OnlineModel)(se.getValue()));
		}
	}
	public void attributeReplaced(HttpSessionBindingEvent se){}
	public static List getList(){
		return(list);
	}
}
然后在web.xml中声明这个监听器：
代码:
<listener>
<listener-class>
com.bupticet.listener.OnlineList
</listener-class>
</listener>
最后在登陆的servlet或者页面中加入如下代码[请做适当修改]：
代码:
java.text.SimpleDateFormat sdf = new java.text.SimpleDateFormat("yyyy年MM月dd日HH:mm:ss");
                    String time = sdf.format(java.util.Calendar.getInstance().getTime());
                    String[] address = IPLocalizer.search(request.getRemoteAddr());
                    session.setAttribute("online",new OnlineModel(userName,request.getRemoteAddr(),time,address[0]+address[1]));
这样就较为完美的实现了一个在线统计系统
 
显示在线统计：

PHP 代码:
<table width="100%" border="0" cellspacing="0" cellpadding="0">
  <tr class="tableHead" align=center>
    <td width='5%' nowrap>序号</a></td>
    <td width="0%">|</td>
    <td width='18%'>姓名</a></td>
    <td width="0%">|</td>
    <td width='20%'>IP</a></td>
    <td width="0%">|</td>
    <td width='30%'>登陆时间</a></td>
    <td width="0%">|</td>
        <td width='27%'>来自于</a></td>
    <td width="0%">|</td>
  </tr>
<%
java.util.List list=com.bupticet.listener.OnlineList.getList();
int onlineNumber = list.size();
int onlinePageCount = 0;
if(onlineNumber%pagesize==0){
    onlinePageCount = onlineNumber/pagesize;
}else{
    onlinePageCount = onlineNumber/pagesize+1;
}
String str = "";
String trbgcolor=Page_trbgcolor;

int i = (pageNum-1)*pagesize;
int j = 0;
for(;i<onlineNumber&&j<pagesize;i++,j++){
    com.bupticet.listener.OnlineModel om = (com.bupticet.listener.OnlineModel)(list.get(i));
    trbgcolor=(trbgcolor==Page_trbgcolor)?"#FFFFFF":Page_trbgcolor;
     str+=" <tr  height='21' align='center' bgcolor='"+trbgcolor+"'>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+(i+1)+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+om.getUserName()+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+om.getIpAddress()+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+om.getLoadTime()+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+om.getAddress()+"</font></td>"+"\n";
           str+="<td width='0%'></td></tr>"+"\n";
}
for(;j<pagesize;j++){
        trbgcolor=(trbgcolor==Page_trbgcolor)?"#FFFFFF":Page_trbgcolor;
     str+=" <tr  height='21' align='center' bgcolor='"+trbgcolor+"'>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+"&nbsp;"+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+"&nbsp;"+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+"&nbsp;"+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+"&nbsp;"+"</font></td>"+"\n";
       str+="<td width='0%'></td>"+"\n";
       str+="<td nowrap><font color='"+Page_warncolor+"'>"+"&nbsp;"+"</font></td>"+"\n";
           str+="<td width='0%'></td></tr>"+"\n";

}
%>
</table> 
  用session监听实现在线统计_Java