直接在SessionListener中就能完成在线人数统计功能 为啥要用RequestListener??????

public class SessionListener implements HttpSessionListener {

private static ArrayList<User> userlist = UserList.getUserlist();

private static User user=null;

public void sessionCreated(HttpSessionEvent arg0) {

String sessionId = arg0.getSession().getId();

if (userlist != null) {

for (int i = 0; i < userlist.size(); i++) {

User u = userlist.get(i);

if (u.getSessionIdByString() == sessionId) {

return;

}

}

}

user = new User();

user.setSessionIdByString(sessionId);

userlist.add(user);

arg0.getSession().getServletContext().setAttribute("user", userlist);

}

public void sessionDestroyed(HttpSessionEvent arg0) {

userlist.remove(user);

arg0.getSession().getServletContext().setAttribute("user", userlist);

}

}

public class User {	private String sessionIdByString="";	public String getSessionIdByString() {		return sessionIdByString;	}	public void setSessionIdByString(String sessionIdByString) {		this.sessionIdByString = sessionIdByString;	}	}

package moedl;

import java.util.ArrayList;

public class UserList {

private static ArrayList<User> userlist = new ArrayList<User>();

public static ArrayList<User> getUserlist() {

return userlist;

}

// public static void setUserlist(ArrayList<User> userlist) {

// UserList.userlist = userlist;

// }

}