<session-config> 
  <session-timeout>1</session-timeout> 
</session-config> 

package com.scx.entity; 
/** 
 * 用户实体类 
 * 
 */ 
public class User { 
  //当前用户的session id 
  private String sessionId; 
  //当前用户的ip地址 
  private String ip; 
  //当前用户第一次访问的时间 
  private String firstTime; 
  public User() { 
    super(); 
  } 
  public String getIp() { 
    return ip; 
  } 
  public void setIp(String ip) { 
    this.ip = ip; 
  } 
  public String getFirstTime() { 
    return firstTime; 
  } 
  public void setFirstTime(String firstTime) { 
    this.firstTime = firstTime; 
  } 
  public String getSessionId() { 
    return sessionId; 
  } 
  public void setSessionId(String sessionId) { 
    this.sessionId = sessionId; 
  } 
} 

package com.scx.listener; 
import java.util.ArrayList; 
import javax.servlet.annotation.WebListener; 
import javax.servlet.http.HttpSessionEvent; 
import javax.servlet.http.HttpSessionListener; 
import com.scx.entity.User; 
import com.scx.util.SessionUtil; 
/** 
 * HttpSessionListener 监听器 
 * 
 */ 
@WebListener 
public class MyHttpSessionListener implements HttpSessionListener{ 
  //当前用户数 
  private int userCounts=0; 
  @Override 
  public void sessionCreated(HttpSessionEvent se) { 
    //sessionCreated 用户数+1 
    userCounts++; 
    //重新在servletContext中保存userCounts 
    se.getSession().getServletContext().setAttribute("userCounts", userCounts); 
  } 
  @Override 
  public void sessionDestroyed(HttpSessionEvent se) { 
    //sessionDestroyed 用户数-1 
    userCounts--; 
    //重新在servletContext中保存userCounts 
    se.getSession().getServletContext().setAttribute("userCounts", userCounts); 
    @SuppressWarnings("unchecked") 
    ArrayList<User> userList=(ArrayList<User>) se.getSession().getServletContext().getAttribute("userList"); 
    String sessionId=se.getSession().getId(); 
    //如果当前用户在userList中 在session销毁时 将当前用户移出userList 
    if(SessionUtil.getUserBySessionId(userList, sessionId)!=null){ 
      userList.remove(SessionUtil.getUserBySessionId(userList, sessionId)); 
    } 
    //将userList集合 重新保存到servletContext 
    se.getSession().getServletContext().setAttribute("userList", userList); 
  } 
} 

package com.scx.listener; 
import java.text.SimpleDateFormat; 
import java.util.ArrayList; 
import java.util.Date; 
import javax.servlet.ServletRequestEvent; 
import javax.servlet.ServletRequestListener; 
import javax.servlet.annotation.WebListener; 
import javax.servlet.http.HttpServletRequest; 
import com.scx.entity.User; 
import com.scx.util.SessionUtil; 

/** 
 * ServletRequestListener 监听器 
 * 
 */ 
@WebListener 
public class MyServletRequestListener implements ServletRequestListener { 
  //用户集合 
  private ArrayList<User> userList; 
  @Override 
  public void requestDestroyed(ServletRequestEvent arg0) { 
  } 
  @SuppressWarnings("unchecked") 
  @Override 
  public void requestInitialized(ServletRequestEvent arg0) { 
    //从servletContext中获的userList 
    userList=(ArrayList<User>) arg0.getServletContext().getAttribute("userList"); 
    //如果servletContext中没有userList对象 初始化userList 
    if(userList==null){ 
      userList=new ArrayList<User>(); 
    } 
    HttpServletRequest request=(HttpServletRequest) arg0.getServletRequest(); 
    //sessionId 
    String sessionId=request.getSession().getId(); 
    //如果当前sessionId不存在集合中 创建当前user对象 
    if(SessionUtil.getUserBySessionId(userList,sessionId)==null){ 
      User user=new User(); 
      user.setSessionId(sessionId); 
      user.setIp(request.getRemoteAddr()); 
      SimpleDateFormat sdf=new SimpleDateFormat("yyyy-MM-dd hh:MM:ss"); 
      user.setFirstTime(sdf.format(new Date())); 
      userList.add(user); 
    } 
    //将userList集合 保存到ServletContext 
    arg0.getServletContext().setAttribute("userList", userList); 
  } 
} 

package com.scx.util; 
import java.util.ArrayList; 
import com.scx.entity.User; 
public class SessionUtil { 
  //根据sessionId判断当前用户是否存在在集合中 如果存在 返回当前用户 否则返回null 
  public static User getUserBySessionId(ArrayList<User> userList,String sessionId) { 
    for (User user : userList) { 
      if(sessionId.equals(user.getSessionId())){ 
        return user; 
      } 
    } 
    return null; 
  } 
}