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From Henry Zongaro <zong...@ca.ibm.com>
Subject Re: newTransformer returns null
Date Thu, 26 Jun 2008 13:15:21 GMT
Hi, Richard.

Richard Jones <richard.d.jones@hp.com> wrote on 2008-06-24 11:54:08 AM:
> Transformer transformer = tFactory.newTransformer(xslt);
> and am finding that "transformer" is null.  This is confusing, as the
> javadocs are explicit on the subject:
>       newTransformer
> public abstract Transformer <http://xml.apache.org/xalan-
> j/apidocs/javax/xml/transform/Transformer.html> *newTransformer*(Source 
> http://xml.apache.org/xalan-j/apidocs/javax/xml/transform/Source.html> 
>                                     throws 
TransformerConfigurationException <
> http://xml.apache.org/xalan-
> j/apidocs/javax/xml/transform/TransformerConfigurationException.html>
>     *Returns:*
>         A |Transformer| object that may be used to perform a
>         transformation in a single |Thread|, never |null|.

This is a bug.  See XALANJ-2376.[1]  The source of the problem was that 
earlier versions of JAXP stated that the default ErrorListener must simply 
report any error in System.err output stream, but never throw exceptions, 
even in the case of a fatalError.  But how could a processor possibly 
return something useful from newTransformer if it had suffered a fatal 

The Xalan-J developers saw only two choices - throw the exception, despite 
the fact that the ErrorListener is supposed to dictate whether an 
exception is thrown, or return null, so that the user would at least be 
alerted to the problem by the subsequent NullPointerException.  The JAXP 
Expert Group considered the problem, and decided that the processor should 
be permitted to throw the exception in the event of a fatal error, even if 
the installed ErrorListener chose not to throw it.  So we made the wrong 
guess on the outcome, and we haven't yet fixed it.

The work-around is to install an ErroListener that always throws the 
reported exception from its fatalError method.

I hope that helps.


[1] https://issues.apache.org/jira/browse/XALANJ-2376
Henry Zongaro
XML Transformation & Query Development
IBM Toronto Lab   T/L 313-6044;  Phone +1 905 413-6044

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