redis如何替代php实现文件存储session的实例

class SessionManager {
  private $redis;
  public function construct(){
    $this->redis = new Redis();
    $this->redis->connect('192.168.0.102', 6379);
    $retval =session_set_save_handler(
      array($this,"open"),
      array($this,"close"),
      array($this,"read"),
      array($this,"write"),
      array($this,"destroy"),
      array($this,"gc")
    );
    session_start();
  }
  public function open($path,$name){
    return true;
  }
  public function close(){
    return true;
  }
  public function read($id){
    $session_value = $this->redis->get($id);
    if($session_value){
      return $session_value;
    }else{
      return "";
    }
  }
  public function write($id,$data){
    if($this->redis->set($id,$data)){
      return true;
    }else{
      return false;
    }
  }
  public function destroy($id){
    if($this->redis->delete($id)){
      return true;
    }else{
      return false;
    }
  }
  public function gc($maxlifetime){
    return true;
  }
  public function destruct(){
    session_write_close();
  }
}

include("SessionManager.php");
new SessionManager();
$_SESSION['user_name']="xxdcsnd@sina.com";

include("SessionManager.php");
new SessionManager();
echo $_SESSION['user_name'];