Response的Content Type的类型

private string CheckType(string filename)
{
    string ContentType;
    switch (filename.Substring(filename.LastIndexOf(".")).Trim().ToLower())
    {
        case ".asf ":
            ContentType = "video/x-ms-asf ";
            break;
        case ".avi ":
            ContentType = "video/avi ";
            break;
        case ".doc ":
            ContentType = "application/msword ";
            break;
        case ".zip ":
            ContentType = "application/zip ";
            break;
        case ".xls ":
            ContentType = "application/vnd.ms-excel ";
            break;
        case ".gif ":
            ContentType = "image/gif ";
            break;
        case ".jpg ":
            ContentType = "image/jpeg ";
            break;
        case "jpeg ":
            ContentType = "image/jpeg ";
            break;
        case ".wav ":
            ContentType = "audio/wav ";
            break;
        case ".mp3 ":
            ContentType = "audio/mpeg3 ";
            break;
        case ".mpg ":
            ContentType = "video/mpeg ";
            break;
        case ".mepg ":
            ContentType = "video/mpeg ";
            break;
        case ".rtf ":
            ContentType = "application/rtf ";
            break;
        case ".html ":
            ContentType = "text/html ";
            break;
        case ".htm ":
            ContentType = "text/html ";
            break;
        case ".txt ":
            ContentType = "text/plain ";
            break;
        default:
            ContentType = "application/octet-stream ";
            break;
    }
    return ContentType;
}