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@c...  
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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