[xmlc] any BCEL (or otherwise bytecode) experts out there? Can't figure something out...

Turns out that since I turned on URL Rewriting to test my 
OutputOptions.set/getURLRewiteAttributes() addition, I have only been using 
the DynamicMLCreatorASM2Impl class which seems to work in all 
cases.  However, I'm now testing fallback to DynamicMLCreatorBCELImpl and 
it doesn't seem to work properly (this means when using dynamic loading, 
which is the case in which the DynamicMLCreator implementations are 
used).  When URL Rewriting is on, the BaseDOMFormatter checks whether the 
current attribute is a URL rewrite attribute.  If this has not been 
specified in OutputOptions, it asks the XMLObject implementation for the 
information.  This, in turn, asks the dom factory implementation if the 
current attribute is a URL rewrite attribute.  The getDomFactory() method 
is used to get the dom factory.  It returns a static reference to the dom 
factory which is set up something like this...

private static final org.enhydra.xml.xmlc.dom.XMLCDomFactory fDOMFactory = 
org.enhydra.xml.xmlc.dom.XMLCDomFactoryCache.getFactory(org.enhydra.xml.xhtml.XHTMLDomFactory.class);


Now, to the point.  When using the ASM2 impl of DynamicMLCreator, 
XMLCDomFactoryCache.getFactory() gets called when the XMLObject 
implementation is loaded.  However, when using the BCEL version, the 
getFactory() method is never called (I added some debugging code to see 
when it was getting called).  Therefore, the "fDOMFactory" static variable 
is null and XMLObjectImpl.getDomFactory(), therefore, returns null causing 
a NullPointerException.  The thing is, the getFactory() call seems to be 
defined in both the ASM2 and BCEL DynamicMLCreator implementations.  Its 
just that only the ASM2 one creates a class that makes a successful call to 
getFactory().  Here's the stack trace I get (slightly modified version of 
the Preview servlet, so don't let the line number there throw you for a 
loop.  Everything else should be the same as what you'd get in your own 
testing)...

java.lang.NullPointerException
        at 
org.enhydra.xml.xmlc.XMLObjectImpl.isURLAttribute(XMLObjectImpl.java:797)
	at 
org.enhydra.xml.io.BaseDOMFormatter.isURLRewriteAttribute(BaseDOMFormatter.java:699)
	at 
org.enhydra.xml.io.BaseDOMFormatter.writeAttributeValue(BaseDOMFormatter.java:638)
        at org.enhydra.xml.io.XMLFormatter.handleAttr(XMLFormatter.java:232)
        at org.enhydra.xml.dom.DOMTraversal.processAttr(DOMTraversal.java:410)
        at org.enhydra.xml.dom.DOMTraversal.processNode(DOMTraversal.java:367)
	at 
org.enhydra.xml.dom.DOMTraversal.processAttrsUnsorted(DOMTraversal.java:333)
        at 
org.enhydra.xml.dom.DOMTraversal.processAttributes(DOMTraversal.java:284)
        at org.enhydra.xml.io.XMLFormatter.writeOpenTag(XMLFormatter.java:262)
        at org.enhydra.xml.io.XMLFormatter.handleElement(XMLFormatter.java:296)
        at org.enhydra.xml.dom.DOMTraversal.processNode(DOMTraversal.java:370)
        at 
org.enhydra.xml.dom.DOMTraversal.processChildren(DOMTraversal.java:268)
        at org.enhydra.xml.io.XMLFormatter.handleDocument(XMLFormatter.java:166)
        at org.enhydra.xml.dom.DOMTraversal.processNode(DOMTraversal.java:358)
        at org.enhydra.xml.dom.DOMTraversal.traverse(DOMTraversal.java:243)
        at org.enhydra.xml.io.BaseDOMFormatter.write(BaseDOMFormatter.java:746)
        at org.enhydra.xml.io.DOMFormatter.write(DOMFormatter.java:205)
        at org.enhydra.xml.io.DOMFormatter.toBytes(DOMFormatter.java:184)
	at 
org.enhydra.xml.xmlc.servlet.XMLCContext.outputDocument(XMLCContext.java:412)
        at 
org.enhydra.xml.xmlc.servlet.XMLCContext.writeDOM(XMLCContext.java:503)
        at xmlc.demo.Preview.service(Preview.java:38)


Both of these DynamicMLCreator implementations were generated based off 
existing XMLC compiled classes and then modified to do exactly what we 
wanted.  My overall knowledge of this bytecode stuff is minimal.  So, is 
there anyone out there that can interpret the DynamicMLCreatorBCELImpl and 
tell me why the getFactory() call is not being made at runtime?  If you 
can, a patch to fix the issue would be very helpful.  This is the last 
thing I need to do before the 2.2.7 release.  I think we need fallback to 
BCEL for environments that can't use ASM2 because it conflicts with 
ASM1.x.x which a number of applications still use.

To test, just turn on URL Rewriting, set the following context param in 
web.xml (make sure to also set up reparse resource dirs and other such 
context params.  For an example, see the Tomcat example app.  In fact, the 
Tomcat app can be used for testing since it is mostly pretty much set to go)...

  <context-param>
    <param-name>xmlcSessionURLEncoding</param-name>
    <param-value>always</param-value>
    <description> </description>
  </context-param>

...And then in your servlet, use the XMLCContext to load up the XMLCFactory...

  XMLCContext context = XMLCContext.getContext(this);
  XMLCFactory factory = context.getXMLCFactory();

  //cast to a deferred parsing factory...
  XMLCDeferredParsingFactory dpFactory = null;
  if (factory instanceof XMLCDeferredParsingFactory) {
      dpFactory = (XMLCDeferredParsingFactory)factory;
  }

  //dynamically load up the file
  XMLObject xmlObj = dpFactory.createFromFile(path);

  //write to the response.  Within this call is where the 
NulPointerException is being thrown
  //when using the BCEL DynamicMLCreator implementation
  context.writeDOM(req, resp, xmlObj);

I've committed a preliminary change to DynamicClassLoader to allow for 
fallback to BCEL when ASM2 is not found in the classpath.  So, when you 
test this, make sure to remove ASM2 from the classpath.  ASM2 is used in 
preference to BCEL if both exist in the classpath.  If anyone can help me 
out here, it would be much appreciated!


thanks,

Jake



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