SAX parser does not resolve filename

Another day, another strange error with SAX, Java, and friends.

I need to iterate over a list of File objects and pass them to a SAX parser. However, the parser fails because of an IOException. However, the various File object methods confirm that the file does indeed exist.

The output which I get:

11:53:57.838 [MainThread] DEBUG DefaultReactionFinder - C:\project\trunk\application\config\reactions\TestReactions.xml
11:53:57.841 [MainThread] ERROR DefaultReactionFinder - C:\project\trunk\application\config\reactions\null (The system cannot find the file specified)

So the problem is obviously that null in the second line. I've tried nearly all variations of passing the file as a parameter to the parser, including as a String (both from getAbsolutePath() and entered by hand), as a URI and, even more weirdly, as a FileInputStream (for this I get the same error, except that the entire relative path gets reported as null, so C:\project\trunk\null).

All that I can think of is that the SAXParserFactory is incorrectly configured. I have no idea what is wrong, though.

Here is the code concerned:

SAXParserFactory factory = SAXParserFactory.newInstance();
factory.setValidating(true);
try {
    parser = factory.newSAXParser();
}
catch (ParserConfigurationException e) {
    throw new InstantiationException("Error configuring an XML parser.  Given error message: \"" + e.getMes开发者_开发技巧sage() + "\".");
}
catch (SAXException e) {
    throw new InstantiationException("Error creating a SAX parser.  Given error message: \"" + e.getMessage() + "\".");
}
...
for (File f : fileLister.getFileList()) {
    logger.debug(f.getAbsolutePath());
    try {
        parser.parse(f, new ReactionHandler(input));
        //FileInputStream fs = new FileInputStream(f);
        //parser.parse(fs, new ReactionHandler(input));
        //fs.close();
    }
    catch (IOException e) {
        logger.error(e.getMessage());
        throw new ReactionNotFoundException("An error occurred processing file \"" + f + "\".");
    }
    ...
}

I have made no special provisions to provide a custom SAX parser implementation: I use the system default. Any help would be greatly appreciated!

Edit More information:

My code when I use streams:

FileInputStream fs = new FileInputStream(f);
InputSource is = new InputSource(fs);
//is.setSystemId(f.toURI().toString());
parser.parse(is, new ReactionHandler(input));

Which gives output

11:07:10.703 [MainThread] DEBUG DefaultReactionFinder - C:\project\trunk\application\config\reactions\TestReactions.xml
11:07:10.706 [MainThread] ERROR DefaultReactionFinder - C:\project\trunk\application\null (The system cannot find the file specified)

which shows that the relative directory of the XML file is not resolved correctly. If I include the line which is commented out, the relative directory is once again resolved correctly. This makes me think that somewhere some setting is incorrect...

Ugh, I should have know... the problem isn't with the code, but with the DOCTYPE definition in the XML file! I gave a public identifier but not a system identifier. This means that the file which the parser could not resolve was not the XML file itself, but rather the DTD file!