public function getRegExp($event_key)
    {
        $pos = strpos($event_key,'*');
        if ($pos === false){
            return null;
        }
        
        $buffer = '';
        $reg_exp = '';
        $length = strlen($event_key);
        
        for($i=0; $i<$length; $i++){
            $c = $event_key[$i];
            if (strpos(self::PREG_METACHARS,$c) !== false){
                if (!empty($buffer)){
                    $reg_exp .= preg_quote($buffer,'/');
                    $buffer = '';
                }
                if ($c == '*'){
                    $reg_exp .= '.*';
                }
                else{
                    $reg_exp .= preg_quote($c,'/');;
                }
            }
            else{
                $buffer .= $c;
            }
        }
        if (!empty($buffer)){
            $reg_exp .= preg_quote($buffer,'/');
        }
        
        return '/^' . $reg_exp . '$/';
    }