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);