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From Edwin Goei <Edwin.G...@eng.sun.com>
Subject Re: Potential Xerces regression (bug# 933)
Date Wed, 14 Mar 2001 00:06:18 GMT
Scott_Boag@lotus.com wrote:
> 
> > JAXP 1.1, which is based on DOM Level 2, exposes a new method to create
> > a DOM Document object to conform to DOM Level 2.  This is the preferred
> > method to create a DOM Level 2 tree:
> >
> > DocumentBuilderFactory dbf = new DocumentBuilderFactory();
> > dbf.setNamespaceAware(true);  // needed b/c default value is false
> > DocumentBuilder db = dbf.newDocumentBuilder();
> > DOMImplementation di = db.getDOMImplementation();  // W3C DOM Impl
> > DocumentType dt = di.createDocumentType("pref:root", pubID, sysId);
> > Document doc = createDocument("http://someuri", "pref:root", dt);
> 
> Edwin, this will not work for XSLT processing with JAXP 1.1.  People want
> to create a Document node and have it populated by the XSLT processor.  In
> order to support this we will have to change
> javax.xml.transform.dom.DOMResult to hold a DOMImplementation that can be
> passed in, so that Xalan can create the document node when an element node
> is created (besides the change in JAXP, this is a fair amount of work in
> Xalan, because this non-node will have to be passed through the entire
> processing flow).

OK well, then using DocumentBuilder.newDocument() will still work.  Here
is the JAXP development timeline: first there was DOM (Level 1) which
did not define a way to create a DOM Document, then JAXP 1.0 appeared
which filled this need by adding DocumentBuilder.newDocument(), then
came DOM Level 2, which added
DOMImplementation.createDocument(rootElement,...), then came JAXP 1.1. 
So the new DOM Level 2 createDocument(rootElement...) creation mechanism
is fundamentally different from JAXP 1.0 b/c it specifies the XML root
element as an argument.  So in JAXP 1.1,
DocumentBuilder.getDOMImplementation() was added to allow apps to create
documents the DOM Level 2 way.

> God, I wish this had been caught 3 months ago.  Perhaps
> we can make that change for JAXP 1.2 or 1.1.1.  But, in any case, the
> Javadoc does not seem to deprecate DocumentBuilderImpl#newDocument() that I
> can see, so there's nothing to say it's "not preferred".  This is a
> flat-out mismatch with DOM2.

Maybe using DocumentBuilder.newDocument() should not be marked
"non-preferred" (deprecated) b/c it adds another way to create a DOM
Document object, which may be useful for apps like Xalan that want to
create a generic DOM Document without a root element.  I am not sure if
it conflicts with DOM b/c I have not had time to keep up to date with
future DOM plans.  Perhaps Joe Kesselman can comment?

BTW, as I understand it, methods are no longer marked with "@deprecated"
b/c this causes compiler warnings.  This issue may need to be cc-ed to
the JSR-63 list (which is where JAXP 1.1 issues are discussed).

> 
> I think that the near term solution to this is that it be documented that
> DocumentBuilder#newDocument() can throw a not supported exception for some
> DOM implementations, and precisely document that the Document returned is
> in a temporarily invalid state that does not match any state recognized by
> the DOM.

I'm not sure I understand the need for this.  Since JAXP is limited to
XML parsing, all implementations will have some class that will
implement the DOM Document interface, so the
DocumentBuilder#newDocument() method can just return a new instance of
that class.  Something else to be discussed on the JSR63 list, perhaps?

-Edwin

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