Session保存到数据库的php类分享

<?php 
class SessionToDB 
{ 
private $_path = null; 
private $_name = null; 
private $_pdo = null; 
private $_ip = null; 
private $_maxLifeTime = 0; 

public function __construct(PDO $pdo) 
{ 
session_set_save_handler( 
array(&$this, 'open'), 
array(&$this, 'close'), 
array(&$this, 'read'), 
array(&$this, 'write'), 
array(&$this, 'destroy'), 
array(&$this, 'gc') 
); 

$this->_pdo = $pdo; 
$this->_ip = !empty($_SERVER['REMOTE_ADDR']) ? $_SERVER['REMOTE_ADDR'] : null; 
$this->_maxLifeTime = ini_get('session.gc_maxlifetime'); 
} 

public function open($path,$name) 
{ 
return true; 
} 

public function close() 
{ 
return true; 
} 

public function read($id) 
{ 
$sql = 'SELECT * FROM session where PHPSESSID = ?'; 
$stmt = $this->_pdo->prepare($sql); 
$stmt->execute(array($id)); 

if (!$result = $stmt->fetch(PDO::FETCH_ASSOC)) { 
return null; 
} elseif ($this->_ip != $result['client_ip']) { 
return null; 
} elseif ($result['update_time']+$this->_maxLifeTime < time()){ 
$this->destroy($id); 
return null; 
} else { 
return $result['data']; 
} 
} 

public function write($id,$data) 
{ 
$sql = 'SELECT * FROM session where PHPSESSID = ?'; 
$stmt = $this->_pdo->prepare($sql); 
$stmt->execute(array($id)); 

if ($result = $stmt->fetch(PDO::FETCH_ASSOC)) { 
if ($result['data'] != $data) { 
$sql = 'UPDATE session SET update_time =? , date = ? WHERE PHPSESSID = ?'; 

$stmt = $this->_pdo->prepare($sql); 
$stmt->execute(array(time(), $data, $id)); 
} 
} else { 
if (!empty($data)) { 
$sql = 'INSERT INTO session (PHPSESSID, update_time, client_ip, data) VALUES (?,?,?,?)'; 
$stmt = $this->_pdo->prepare($sql); 
$stmt->execute(array($id, time(), $this->_ip, $data)); 
} 
} 

return true; 
} 

public function destroy($id) 
{ 
$sql = 'DELETE FROM session WHERE PHPSESSID = ?'; 
$stmt = $this->_pdo->prepare($sql); 
$stmt->execute(array($id)); 

return true; 
} 

public function gc($maxLifeTime) 
{ 
$sql = 'DELETE FROM session WHERE update_time < ?'; 
$stmt = $this->_pdo->prepare($sql); 
$stmt->execute(array(time() - $maxLifeTime)); 

return true; 
} 
} 

try{ 
$pdo = new PDO('mysql:host=localhost;dbname=rphp4zf', 'root','rickyfeng'); 
$pdo->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION); 

new SessionToDB($pdo); 
} catch(PDOException $e) { 
echo 'Error: '.$e->getMessage(); 
}