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From "Andy Carlson" <andyslist...@hotmail.com>
Subject Re: JAXP (in)compatability between Xerces and Crimson
Date Fri, 09 Nov 2001 17:08:22 GMT
Shane,

Thanks for your reply. Looks like there may be hope on the horizon!

And to think that when I started composing the mail I thought it was going 
to be a bug report which could get fixed quickly. I later realised that I 
couldnt really either a) find a specific bug or b) blame any single 
component, just the whole process.

Oh well... I suppose we would be out of a job if everything worked like you 
wanted it to.

Cheers,
Andy
----------------------------------------------------------------
Andy Carlson



>From: Shane_Curcuru@lotus.com
>Reply-To: general@xml.apache.org
>To: general@xml.apache.org
>Subject: Re: JAXP (in)compatability between Xerces and Crimson
>Date: Fri, 9 Nov 2001 11:50:27 -0500
>
>One ray of (potential) hope is the first product from the xml-commons
>subproject: xml-apis.jar.  We haven't yet had an official release yet,
>although I just might do one soon to match Xalan's planned 2.2D12 release
>in the next day or so.
>
>The point of xml-apis.jar is to hold externally-defined standards based XML
>related files, to use a few too many adjectives.  This essentially means
>our own copies of DOM L2, SAX 2.x and JAXP 1.1.x.  If we can get a number
>of other subprojects to cooperate, we can all get these common and usually
>backwards-compatible standards files from the same place: xml-apis.jar.
>We're hoping that will be a reasonable solution to the mismatched JAXP
>problems.
>
>---- you  "Andy Carlson" <andyslistbox@hotmail.com> wrote ----
> > Hi all, I've just spent quite a while tracking down a weird problem...
>I'm running a servlet under Tomcat 4.0. The servlet includes Axis, which in
> > this case is using the Xerces (1.4.3) parser. Everything works fine - no
> > problem so far... Now I try to run the same servlet on Tomcat 4.0
>embedded in JBoss (2.4.1)
> > and I get the following:
> > - java.lang.ClassCastException:
> > org.apache.crimson.jaxp.DocumentBuilderFactoryImpl
> > at
>javax.xml.parsers.DocumentBuilderFactory.newInstance(DocumentBuilderFactory.java:152)
>
>
>
> > So what's the answer?
> > - at the moment the answer seems to be to avoid mixing Crimson and 
>Xerces
>in
> > the same context unless you have a very good understanding of how they
>are
> > going to interact with each other - you might get away with it or you
>might
> > (like me) spend a long time chasing strange problems.
>Yup, especially since JAXP has undergone some changes in exactly how it
>looks up factories recently that make the code behave differently and have
>different classes (under the covers).  But there are a lot of other
>situations (depends on servlet container and some specific parser versions)
>where I've had multiple parsers play happily.
>
> > ... but this is bad news because it means that if my servlet uses an XML
> > parser, I have to check whether the app server I'm deploying on is using
> > another one in a way which is going to cause a conflict.
>Ah - part of the solution is JAXP, which means at least you shouldn't have
>to change your code - just perhaps change part of the environment without
>recompiling etc.  So, part of this issue also lies with various servlet
>containers, which each may have hidden quirks with classloaders etc.
>
> > - For the future it would seem to be a better approach to agree on a
>single
> > implementation of JAXP within Apache, put it in its own JAR and
>explicitly
> > disallow (in the JAXP spec?) XML parser implementations from
>reimplementing
> > all or part of JAXP in their own JARs.
>Interesting point; but there's a fine line between defining a high-level
>spec like JAXP and specifying too many implementation details without solid
>enough history behind them.  In the end, the real decision is with Sun,
>since they own the core JAXP spec; Apache will just continue providing some
>useful implementations thereof...
>
>- Shane
>
>
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