I solved this problem in a different that is less destructive. This
also works to replace a DTD with a different one or to force validation
on a schema even if a non-existant DTD is specified.
This particular implementation requires using the SAXParser but I
belive the idea would work with other parsers that provide similar
functionality,
namely an override of "resolveEntity". The key trick is to resolve all
DTD's with a "NullInputStream" ( these are trivial to write so I wont
supply the code here)
An empty DTD file validates any XML (atleast it does in my tests).
Here's the snippet
private class ValidatorHandler extends DefaultHandler {
..... // other methods as needed
@Override
public InputSource resolveEntity(String publicId, String
systemId) throws IOException,
SAXException {
if( systemId.toLowerCase().endsWith(".dtd"))
return new InputSource( new NullInputStream());
else
return super.resolveEntity(publicId, systemId);
}
}
SAXParserFactory f = SAXParserFactory.newInstance();
.... setup the factory
SAXParser parser = f.newSAXParser();
... setup the parser
parser.parse(xml, new ValidatorHandler());
David A. Lee
dlee@calldei.com
http://www.calldei.com
http://www.xmlsh.org
812-482-5224
Mike Sokolov wrote:
4A9FC3FB.60600@ifactory.com" type="cite">After
all the discussion about "What is data?" I don't know if this list is
the place to discuss actual details of implementation, but please feel
free to send me elsewhere if you can think of a better venue.
I have a need to handle XML that references a non-existent DTD. The
DTD is irrelevant to the actual processing of the XML, and isn't
available anywhere, but it is declared in in the DOCTYPE. I'm sure
many of you have encountered this situation: it's practically the norm,
in my experience.
After years of dealing with this inherently unsatisfactory situation in
a variety of ways, I came up with a new one that I am liking at the
moment, which is to insert a Stream into a Java XML processing stack
that strips out the prolog of the XML document before handing it off to
a parser. This has the nice property that it doesn't require
modifications to the stored XML files. It loses PIs and comments and
the XML decl, but I can live with that.
My question is twofold:
1) does the following code snippet actually do what it is claiming to?
Does anybody see any obvious mistakes? My knowledge of the format of
DOCTYPE decls and so on is somewhat limited. I read the spec and this
seems to work on the examples I have, but I suspect there are some
cases I'm not handling.
2) Is there a better approach? Existing code to do the same thing?
Some way to tell parsers to ignore the DOCTYPE (even though that seems
to run counter to the spec)?
Thanks for your attention...
-Mike Sokolov
/**
* An InputStream for XML that strips off the prolog of an XML
* document. The idea is to avoid having to prevent parsers from
attempting
* to process an external DTD.
*
* @author sokolov
*
*/
class XmlNoPrologInputStream extends PushbackInputStream {
XmlNoPrologInputStream (InputStream base) throws
IOException {
super (base, 2);
int c;
while ((c = read()) >= 0) {
if (c == '<') {
int c1 = read();
if (c1 < 0) {
// ill-formed
reset();
return;
}
// XML declaration, PI, comment or DOCTYPE
if (c1 == '?' || c1 == '!')
continue;
// must be the start of the document: arrange to
begin
// reading here
unread(c1);
unread(c);
return;
}
}
}
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