JavaWeb中的Session、SessionListener、在线人数统计

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JavaWeb中的Session

在JavaWeb中使用HttpSession（以下简称session）对象来表示一个会话。
正在装载数据……
Session的创建（代表会话周期的开始）：第一次调用request.getSession()方法时，会创建一个session对象。
Session的销毁（代表会话周期的结束）：在某个请求周期内调用了Session.invalidate()方法，此请求周期结束后，session被销毁；或者是session超时后自动销毁。
对于JSP，如果指定了<%@ page session="false"%>，则在JSP中无法直接访问内置的session变量，同时也不会主动创建session，因为此时JSP未自动执行request.getSession()操作获取session。
在session对象刚创建的第一个请求周期内，调用session.isNew()方法将得到true。
可以在web.xml文件中配置session默认的超时时间（分钟）：

< session-config >
< session-timeout > 10 session-timeout >
session-config >

也可以调用session. setMaxInactiveInterval()方法设置session超时时间（分钟）

SessionListener

通过SessionListenr可以监听session的创建和销毁，步骤：
1.写一个类MySessionListener，实现javax.servlet.http.HttpSessionListener接口及其sessionCreated()、sessionDestroyed()方法
2.在web.xml中配置SessionListener：

< listener >
< listener-class > MySessionListener类全名 listener-class >
listener >
当 session被创建和销毁时，容器会分别调用SessionListener的sessionCreated()方法和 sessionDestroyed()方法，这两个方法中传入了一个参数对象HttpSessionEvent，可以通过此对象的 getSession()方法获取session对象。

应用：在线人数统计

import java.util.HashSet;
import javax.servlet.ServletContext;
import javax.servlet.http.HttpSession;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class MySessionListener implements HttpSessionListener {

        public void sessionCreated(HttpSessionEvent event) {
               HttpSession session = event.getSession();
               ServletContext application = session.getServletContext();

               // 在application范围由一个HashSet集保存所有的session
               HashSet sessions = (HashSet) application.getAttribute( " sessions " );
               if (sessions == null ) {
                      sessions = new HashSet();
                      application.setAttribute( " sessions " , sessions);
               }

               // 新创建的session均添加到HashSet集中
               sessions.add(session);
               // 可以在别处从application范围中取出sessions集合

              // 然后使用sessions.size()获取当前活动的session数，即为“在线人数”
        }

        public void sessionDestroyed(HttpSessionEvent event) {
               HttpSession session = event.getSession();
               ServletContext application = session.getServletContext();
               HashSet sessions = (HashSet) application.getAttribute( " sessions " );

               // 销毁的session均从HashSet集中移除
               sessions.remove(session);
        }
}

package stat;

import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpSessionAttributeListener;
import javax.servlet.http.HttpSessionBindingEvent;
import javax.servlet.http.HttpSessionBindingListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

public class OnlineCounter extends HttpServlet implements HttpSessionListener,
    HttpSessionAttributeListener,HttpSessionBindingListener {
public OnlineCounter(){
    System.out.println("OnlineCounter initialized.");
}
private static final long serialVersionUID = 1L;

private static int sessionCounter = 0;

private static int attributeCounter = 0;

public void sessionCreated(HttpSessionEvent se) {
    sessionCounter++;
    System.out.println("session created:" + sessionCounter);
}

public void sessionDestroyed(HttpSessionEvent se) {
    sessionCounter--;
    System.out.println("session destroied");
}

public void attributeAdded(HttpSessionBindingEvent se) {
    attributeCounter++;
    System.out.println("attribute added :" + attributeCounter);
}

public void attributeRemoved(HttpSessionBindingEvent se) {
    attributeCounter--;
    System.out.println("attribute removed");
}

public void attributeReplaced(HttpSessionBindingEvent se) {
    System.out.println(se.getName()+" replaced");
}

public void valueBound(HttpSessionBindingEvent event){
      System.out.println(event.getName()+"_Bound_"+event.getValue());
}

public void valueUnbound(HttpSessionBindingEvent event) {
    System.out.println(event.getName()+"_Unbound_"+event.getValue());
}

public static int getOnlineSession() {
    return sessionCounter;
}
public static int getOnlineAttribute() {
    return attributeCounter;
}
}

统计在线人数..sessionCreated中添加ip判断

package com.asiainfo.sale.common;

import javax.servlet.http.*;
import javax.servlet.ServletException;
import java.io.IOException;
import java.util.Date;
import java.util.ArrayList;
import java.sql.Timestamp;
import javax.servlet.ServletRequestListener;
import javax.servlet.ServletRequestEvent;

public class SessionCounter implements HttpSessionListener,ServletRequestListener {
    private static final String CONTENT_TYPE = "text/html; charset=GBK";
    private static int activeSessions = 0;
    private HttpServletRequest request;
    private static ArrayList list = new ArrayList();

public void init() throws ServletException {

}

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        response.setContentType(CONTENT_TYPE);
        HttpSession session = request.getSession();
    }

public void destroy() {
}

    public void requestDestroyed(ServletRequestEvent event) {
        //To change body of implemented methods use File | Settings | File Templates.
    }

    public void requestInitialized(ServletRequestEvent sre){
        request=(HttpServletRequest)sre.getServletRequest();
    }

    public void sessionCreated(HttpSessionEvent httpSessionEvent) {
        String sessionId = httpSessionEvent.getSession().getId();
        Timestamp createTime = new Timestamp(System.currentTimeMillis());
        String loginIp = request.getRemoteAddr();
        boolean rs = true;
        if(list.size() > 0){
            for(int i = 0;i < list.size(); i ++){
                if(loginIp.equals(list.get(i))){
                    rs = false;
                }
            }
        }
        if(rs){                      //如果队列中存在相同的IP 则SESSION不增加
            list.add(loginIp);
            System.out.println("ipList队列新增ip: "+loginIp);
            activeSessions++;
            System.out.println("新增SESSION,sessionId = " + sessionId +"; createTime = " + createTime
                             + "; loginIp = " + loginIp +"; 当前总SESSION值为 "+activeSessions);
        }
    }

    public void sessionDestroyed(HttpSessionEvent httpSessionEvent) {
        String sessionId = httpSessionEvent.getSession().getId();
        Timestamp overTime = new Timestamp(System.currentTimeMillis());
        String loginIp = request.getRemoteAddr();
        if(activeSessions>0){
            if(list.size() > 0){
                for(int i = 0;i < list.size(); i ++){
                    if(loginIp.equals(list.get(i))){
                        list.remove(i);
                        System.out.println("ipList队列移除ip: "+loginIp);
                    }
                }
            }
            activeSessions--;                   //在用户销毁的时候,从队列中踢出这个IP
            System.out.println("销毁SESSION,sessionId = " + sessionId +"; overTime = " + overTime
                             + "; loginIp = " + loginIp +"; 当前总SESSION值为 "+activeSessions);
        }
    }