Clone a DOM subtree to the root of a new DOMDocument efficiently ?

[Chris Cheung]

Dear all,

  Very often I need to clone a DOM subtree to a new DOMDocument and make 
the root of the subtree be the document element of the new DOMDocument.
However, it seems that in Xerces-C++/Perl, the document element is 
created when creating the DOMDocument (via 
DomImplementation::createDocument) and cannot be replaced afterward.
Hence I cannot use the DOMDocument::importNode to directly deep clone the
root node of the source subtree, but rather I have to copy its 
attributes and child nodes one by one (in Perl code):

sub element2Doc
{
    my ($element) = @_;

    # Create a new DOM Document
    my $domImpl =
        XML::Xerces::DOMImplementationRegistry::getDOMImplementation('LS')

    my $newDoc = $domImpl->createDocument($element->getNamespaceURI,
        $element->getTagName, undef);

    # Need to copy every attribute and every child node,
    # (Since these is no API to set document element of a DOMDocument.)
    my $newRoot = $newDoc->getDocumentElement();
    my $attrs = $element->getAttributes();

    for (my $i = 0; $i < $attrs->getLength; $i++)
    {
        my $attr = $attrs->item($i);
        my $nsURI = $attr->getNamespaceURI;
        if ($nsURI)
        {
            # The attribute is qualified
            $newRoot->setAttributeNS($nsURI, $attr->getName, 
                $attr->getValue);
        }
        else
        {
            $newRoot->setAttribute($attr->getName, $attr->getValue);
        }
    }

    my @childNodes = $element->getChildNodes();
    foreach (@childNodes)
    {
        my $copiedChild = $newDoc->importNode($_, 1);
        $newRoot->appendChild($copiedChild);
    }
    return $newDoc;
}


Using the Xerces-Perl wrapper over the efficient Xerces-C++ library,
the code runs slowly since a lot of Perl statements are executed each 
calls short C++ methods, especially for broad but not deep source DOM 
subtree.

Is there any smarter way to do the same thing?
Thank you in advance for any help.

-- 
Best Regards,

Chris Cheung
Center for Large-Scale Computation

Have a nice day!



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