// Use an XML object or an Array. This array is just an example
var _arrLinks:Array = ["testfiletype.txt", "http://www.domain.com/", "something.fdz", "another-file.rtf", "www.somedomain.com", "domain.com"];
var _fileExt:String;
var _strTmp:String;
for (var i:uint = 0; i < _arrLinks.length; i++)
{
	_strTmp = _arrLinks[i];
	_fileExt = _strTmp.substr(0, 4);
	
	if (_fileExt == "www.") _fileExt = "www";
	else if (_fileExt != "http") _fileExt = _strTmp.substr(_strTmp.lastIndexOf('.') + 1, _strTmp.length);
	
	switch (_fileExt)
	{
		case "swf":
			trace("This is a SWF file: " + _strTmp);
			break;
		case "txt":
			trace("This is a TXT file: " + _strTmp);
			break;
		case "http":
			trace("This is an HTTP link: " + _strTmp);
			break;
		case "www":
			trace("This is a WWW link, convert to an HTTP link: http://" + _strTmp);
			break;
		case "com":
			trace("This is a dot com link, convert to an HTTP link: http://" + _strTmp);
			break;
		default:
			trace("Unrecognized link or file extension. Please add (" + _fileExt + ") to the switch statment or change your filename.");
			break;
	}
}

Works great for parsing links in XML documents and arrays.

Determine File Extension

file, extension

ActionScript 3