Tag Archives: programming

Groovy, null, and ‘null’

Groovy will let you call toString() on a null object. The result is the word ‘null’, which might be what you’re expecting if you know the object is null, but probably isn’t what you’re expecting if you don’t.

So if you’re, say, binding a SQL parameter and you forget to check for nulls like you would in Java, and you forget to use a null-safe operator like you should in Groovy, and you get a null value, what happens? Does groovy…

  1. Throw a NullPointerException like Java?
  2. Set the field to null?

Neither. It sets the field to the string ‘null’.

Make sure to use myVariable?.toString() instead of myVariable.toString() for cases like this!

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.

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All right, all right! ) Happy now?