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:
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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