Thanks!
I did some testing to see how OpenBD and Lucee would handle each variation of the request.
Lucee accepts:
<cfset results.folder = getPageContext().getRequest().getAttribute( "javax.servlet.error.request_uri" )>
Lucee rejects:
<cfset results.folder = "#request.javax.servlet.error.request_uri#">
OpenBD accepts:
<cfset results.folder = getPageContext().getRequest().getAttribute( "javax.servlet.error.request_uri" )>
<cfset results.folder = "#request.javax.servlet.error.request_uri#">