Re: [xml-dev] NullPointerException

Yvonne Aburrow wrote:
> Hi, my Apache FOP engine keeps throwing a NullPointerException every 
> time I try to transform an XML file using a particular XSL.  (Files are 
> at <http://people.bath.ac.uk/ccsya/library/> and the offending XSL is 
> <http://people.bath.ac.uk/ccsya/library/libraryguides.xsl>.)  I'm using 
> Java 1.4.2 and have checked it works with a previous XSL.  I tried 
> validating it with the FO DTD offered by RenderX, but it was no help (it 
> threw an error at <xsl:stylesheet>).  I'm using XMLSpy version 5 rel 4.
> 
> Any help would be much appreciated

First, you have to realize that generating PDF from arbitrary
XML is a two stage process: first a transformation, which generates
a XML document using the XSLFO vocabulary, then the actual formatting
of the XSLFO into PDF. You can't validate the style sheet against a
FO DTD, only the result of the transformation. In order to track down
the problems, run the XSLT standalone and generate an XSLFO document,
which can then be validated against the DTD (after you fixed the
problems with the style sheet itself

Secondly, XMLSpy 5.4 contains an older release of FOP. In particular,
the current release 0.20.5 generates more sensible error messages for
many of the common problems which caused NPEs.
You can get the latest FOP release from
  http://xml.apache.org/fop/download.html
Read
  http://xml.apache.org/fop/running.html
and specifically
  http://xml.apache.org/fop/running.html#check-input
for running FOP without XML Spy.

Thirdly, there are more appropriate places to ask for help first:
- The Altova help desk
- The FOP user list
    http://xml.apache.org/fop/maillist.html#fop-user
  for FOP specific problems
- The XSL list
    http://www.mulberrytech.com/xsl/xsl-list/
  for general XSL related problems and specifically for XSLT questions.

J.Pietschmann