将Session写入数据库

使用session_set_save_handler()函数，将Session的内容写入数据库

<?php
    /*
    *@author    Fahy
    *@link    http://home.cnblogs.com/u/HuangWj
    *数据库为mysql，
    *数据库名为session，表名为session，
    *表中字段包括PHPSESSID,update_time,client_ip,data
    */
    class Session{
        private static $handler = null;
        private static $ip = null;
        private static $lifetime = null;
        private static $time = null;
        
        //配置静态变量
        private static function init($handler){
            self::$handler = $handler;        //获取数据库资源
            self::$ip = !empty($_SERVER["REMOTE_ADDR"])? $_SERVER["REMOTE_ADDR"]:'unkonw';        //获取客户端ip
            self::$lifetime = ini_get('session.gc_maxlifetime');        //获取session生命周期
            self::$time = time();        //获取当前时间
        }
        //调用session_set_save_handler()函数并开启session
        static function start($pdo){
            self::init($pdo);
            session_set_save_handler(
                array(__CLASS__,'open'),
                array(__CLASS__,'close'),
                array(__CLASS__,'read'),
                array(__CLASS__,'write'),
                array(__CLASS__,'destroy'),
                array(__CLASS__,'gc')
            );
            session_start();
        }
        
        public static function open($path,$name){
            return true;
        }
        public static function close(){
            return true;
        }
        
        //查询数据库中的数据
        public static function read($PHPSESSID){
             $sql = "select PHPSESSID,update_time,client_ip,data from session where PHPSESSID=?";
             $stmt = self::$handler->prepare($sql);
             $stmt->execute(array($PHPSESSID));
             if(!$result = $stmt->fetch(PDO::FETCH_ASSOC)){
                 return '';
             }
             if(self::$ip == $result['client_ip']){
                 self::destroy($PHPSESSID);
                 return '';
             }
             if(($result['update_time']+self::$lifetime)<self::$time){
                 self::destroy($PHPSESSID);
                 return '';
             }
             return $result['data'];
        }
        /*
         *首先查询该session是否存在数据，如果存在，则更新数据，如果不存在，则插入数据
         */
        //将session写入数据库中，$data传入session中的keys和values数组
        public static function write($PHPSESSID,$data){
            $sql = "select PHPSESSID,update_time,client_ip,data from session where PHPSESSID=?";
             $stmt = self::$handler->prepare($sql);
             $stmt->execute(array($PHPSESSID));
             
             if($result=$stmt->fetch(PDO::FETCH_ASSOC)){                
                 if($result['data'] != $data || self::$time > ($result['update_time']+30)){
                     $sql = "update session set update_time=?,data=? where PHPSESSID = ?";
                     $stmt = self::$handler->prepare($sql);
                     $stmt->execute(array($self::$time,$data,$PHPSESSID));
                }
             }else{
                 if(!empty($data)){
                     try{
                         $sql = "insert into session(PHPSESSID,update_time,client_ip,data) values(?,?,?,?)";
                     }catch(PDOException $e){
                         echo $e->getMessage();
                     }
                     $sth = self::$handler->prepare($sql);
                     $sth->execute(array($PHPSESSID,self::$time,self::$ip,$data));
                 }
             }
             return true;
        }
        
        public static function destroy($PHPSESSID){
            $sql = "delete from session where PHPSESSID = ?";
            $stmt = self::$handler->prepare($sql);
            $stmt->execute(array($PHPSESSID));
            return true;
        }
        public static function gc($lifetime){
            $sql = "delete from session where update_time<?";
            $stmt = self::$handler->prepare($sql);
            $stmt->execute(array(self::$time-$lifetime));
            return true;
        }
    }
    //使用PDO连接数据库
    try{
        $pdo = new PDO("mysql:host=localhost;dbname=session","root","hwj193");
    }catch(PDOException $e){
        echo $e->getMessage();
    }
    //传递数据库资源
    Session::start($pdo);