php实现将Session写入数据库

<?php
  /*
  *@author  fahy
  *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);