TIL: Generating .xlsx Files with CFML - An Easy Way to Reduce File Size

Just a quick note about generating XLSX (Excel) files with ColdFusion, which basically amounts to me regurgitating the documentation. It’s a small change in code, but the reduction in spreadsheet file size can be considerable.

Some Background

I’ve been under the (mistaken) impression that when generating spreadsheet files with ColdFusion, my options were limited to XLS or CSV. I would generate the former using the built-in spreadsheet functions (spreadsheetNew()) and the latter by manually assembling strings into a comma-delimited format.

While I’m a big fan of the plaintext, interoperable nature of the CSV, some clients explicitly request Excel sheets - so they get their XLS files. These were always “good enough” for the basic reports they were requesting.

Nevertheless, it bothered me that I was using an outdated format for Excel files. My core frustration was practical - XLS files are so much larger than their XLSX counterparts - but this was never enough of a bother to warrant further investigation.

The Code

Consequently, I was happily surprised to discover that spreadsheetNew() provides a second boolean argument, xmlFormat, which indicates if the spreadsheet should be created in the XLSX format - it’s right there in the docs - somehow I’ve just always missed it. Here’s the complete method signature:

spreadsheetNew( [sheetname] [, xmlFormat] );

The xmlFormat option defaults to false, generating an XLS file - and that’s how I’d been using it for all these years. Sigh.

Here’s an example generating a spreadsheet, first using the default XLS approach, and then setting xmlFormat to true, in order to generate an XLSX file:

// legacy approach
filePath = expandPath( '/' ) & 'test.xls';
sheet = spreadsheetNew( 'XLS Test' );

for (i=1; i<=100; i++) {
  spreadsheetAddRow( sheet, i );
}

spreadsheetWrite( sheet, filePath, true );

// XLSX approach
xlsxFilePath = expandPath( '/' ) & 'test.xlsx';
xlsxSheet = spreadsheetNew( 'XLSX Test', true );

for (i=1; i<=100; i++) {
  spreadsheetAddRow( xlsxSheet, i );
}

spreadsheetWrite( xlsxSheet, xlsxFilePath, true );

In order to save it as an XLSX file, the only difference was setting the xmlFormat to true (and updating the file extension).

To take a look at the benefit of this change, let’s compare file sizes:

sheetSize = getFileInfo( filePath ).size;
xlsxSheetSize = getFileInfo( xlsxFilePath ).size;
bytesSaved = sheetSize - xlsxSheetSize;
change = ( bytesSaved / sheetSize )*100;
writeOutput( "File size reduced by #round( change )#% ");
// File size reduced by 54%

Sure enough, the resulting XLSX file is less than half the size of the identical XLS one. That’s a pretty big win for one very small change in code.

A Note for Lucee CFML Users

The Spreadsheet Functions provided by Adobe ColdFusion are not natively supported in Lucee. Fortunately, it’s not too much work to add them, as I’ve previously blogged: How Not To Use Spreadsheet Functions in Lucee.

Read that post for a more detailed exploration of using spreadsheet functions in Lucee, but the TLDR; is that there are two basic approaches:

  1. Install the cfspreadsheet extension. This can be done programmatically or via the Lucee admin.
  2. Take an altogether different approach and use Julian Halliwell’s cfsimplicity/lucee-spreadsheet standalone library for spreadsheet manipulation.

Happy spreadsheeting!