JAVA，用户是否在线，是否登录，在线统计等方法。

package com.oddel.listener;

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

public class SessionListener implements HttpSessionListener {

public void sessionCreated(HttpSessionEvent event) {

// TODO Auto-generated method stub
HttpSession session=event.getSession();

        SessionBean sessionBean=SessionFactory.getInstance().getSessionBean();
       
        /**
         * 访问次数统计
         * */
        sessionBean.setAccessCount(sessionBean.getAccessCount()+1);
       
        /**
         * 在线人数统计
         * */
        sessionBean.getOnline().put(session.getId(), null);
       
}

public void sessionDestroyed(HttpSessionEvent event) {

HttpSession session=event.getSession();
       
        SessionBean sessionBean=SessionFactory.getInstance().getSessionBean();
       
        sessionBean.getLogin().remove(sessionBean.getOnline().get(session.getId()));
       
        sessionBean.getOnline().remove(session.getId());
    }
}



package com.oddel.listener;

import javax.servlet.http.HttpSession;

public class SessionFactory {

private static SessionFactory factory;
private SessionBean sessionBean=new SessionBean();

private SessionFactory(){}

static{
factory=new SessionFactory();
}

public synchronized  static SessionFactory getInstance() {
        if (factory == null) { 
        factory = new SessionFactory();
        } 
       return factory;
   }

public void addLogin(HttpSession session, String user){
this.getSessionBean().getOnline().put(session.getId(), user);
this.getSessionBean().getLogin().add(user);
}

public void removeLogin(HttpSession session, String user){
this.getSessionBean().getLogin().remove(this.getSessionBean().getOnline().get(session.getId()));
this.getSessionBean().getOnline().remove(session.getId());
}

public boolean isOnline(String user){
return this.getSessionBean().getLogin().contains(user);
}

public SessionBean getSessionBean() {
return sessionBean;
}

public void setSessionBean(SessionBean sessionBean) {
this.sessionBean = sessionBean;
}
}

package com.oddel.listener;

import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;

public class SessionBean {

private Map<String,String> online=new HashMap();//在线
private int accessCount=0;//系统访问人数
private Set<String> login=new HashSet();//已经登录用户


/**
* 返回当前系统在线人数
* @return int
*/
public int getOnlineCount(){
return this.getOnline().size();
}

/**
* 返回当前系统登录人数
* @return int
*/
public int getLoginCount(){
return this.getLogin().size();
}

public Map<String, String> getOnline() {
return online;
}

public void setOnline(Map<String, String> online) {
this.online = online;
}

public int getAccessCount() {
return accessCount;
}

public void setAccessCount(int accessCount) {
this.accessCount = accessCount;
}

public Set<String> getLogin() {
return login;
}

public void setLogin(Set<String> login) {
this.login = login;
}

}

Web.xml添加：

<listener>
<listener-class>
com.oddel.listener.SessionListener
</listener-class>
</listener>

用户登录时调用：
SessionFactory.getInstance().addLogin(httpSession, userid);

页面调用：
import="com.oddel.listener.SessionFactory;
SessionFactory.getInstance().isOnline(userid)
返回true表示用户当前是在线的。
返回false表示用户当前是不在线的。
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