Category Archives: Web Design

cfspreadsheet + GetTempFile() = NullPointerException

Every once in a while I encounter a problem with something so blindingly simple that

  1. I can’t imagine I haven’t tried it before, and
  2. I can’t believe no one else has documented the problem either.

ColdFusion 9 and later has a tag called <cfspreadsheet> which makes it dead simple to read, update, or create an Excel file. Want to plug the results of a query into a spreadsheet? Literally one tag with just three parameters.

There’s also function GetTempFile() that will create a guaranteed unique file on the server that you can then manipulate.

The obvious solution if you want to create a spreadsheet to download is to create a temp file, write to it with cfspreadsheet, then serve it up.

<cfset filename=GetTempFile(GetTempDirectory()) >
<cfspreadsheet action="write" overwrite="true" filename="#filename#" query="myquery">
<cfheader name="Content-disposition" value="attachment;filename=MyFile.xls">
<cfcontent type="application/msexcel" file="#filename#">
<cffile action="delete" file="#filename#">

It turns out this won’t work. You’ll get a Null Pointer Exception in the logs. Not because of anything you’d expect, though…it turns out that cfspreadsheet is relying on the file extension, and since GetTempFile() gives you a file ending in .tmp instead of .xls, it isn’t sure what to do with the file.

Solution: Find some other way to name your temporary file, and give it an .xls extension.

A matter of perspective

Last week, the webcomic XKCD ran a strip, Umwelt. Or perhaps it would be better to describe it as several comic strips.

As explained in the mouseover text, the title refers to the idea that because animals have different senses, each animal effectively inhabits a different reality. This can philosophically be extended to human perceptions.

Keeping that in mind, make sure you read it in a few different web browsers (both desktop and mobile!) for the full effect (JavaScript required). And try resizing the window.

As an art project, it’s the best use of browser-sniffing I’ve ever seen.

Recent Tech Links: Unmaintainable Code, XKCD on The Cloud and More

Recent Links: Comic Strips, Moon, Hotspot Safety, Flash Forward and More

Comic strips and art:

Sci-fi and fantasy:

  • Keeping Up With the Cardassians. For months, this is what I heard every time someone mentioned the Kardashians. (What can I say? My brain is more attuned to Star Trek than to reality TV.)
  • Author Robert J. Sawyer answers pointed questions about Flashforward and the TV adaptation, including what went wrong. I have to agree that it was really hurt by focusing too heavily on the conspiracy arc.


Tech stuff: