class A{ 
    public $name;
    protected $age;
    private $code;
    public function __construct($name,$age,$code)
    {
        $this->name = $name;
        $this->age = $age;
        $this->code = $code;
    }
    public function __sleep()
    {
        return ['code'];
    }
}
$a_obj = new A("bihuo",18,'12345');
$str = serialize($a_obj);
echo urlencode($str);