Re: [digester] Multiple Digester Instances

Tue, 14 Oct 2003 15:13:54 -0700

Simon Kitching wrote:

Hi Robert,

On Wed, 2003-10-15 at 09:45, Robert Grey wrote:


Actually I resolved the problem by creating a "cache" of digester objects in a Vector before the application starts. Then I pull those objects off one by one as I need them. It seems that if I intialize a new Digester object after parsing has started it begins to create the "null pointers" which occur in various places. I am using the same rules object I created in the beginning because all of the XML files are the same, I just hoped to split them into multiple files for sake of coherence in our application. Could that be the problem? Here is an example of one of the "null pointers":



Unfortunately, I don't think that reusing rules will work.



Yep ... that is definitely true. You would OK creating clones of the rule instances, but they each contain an internal pointer back to the Digester that owns them, so trying to reuse them will definitely confuse things.

Rule objects contain a reference to their owning Digester object. This
is set when you add a rule to a digester, or set for all Rule object
owned by a Rules object (yecch, hate that naming) when the Rules object
is added to a Digester. So adding the same Rule object to multiple
Digester objects will cause problems; the rules end up having a
reference to the last Digester object they happen to have been added to.
When fired in the context of some other Digester, if they do something
like:
 digester.getMatch(), or digester.push()
they will be referencing the wrong Digester object. Not good.

I think that it is ok to reuse rules *after* a parse has completed, eg
* create rules
* add to digester1
* digester1.parse()
* after parse is complete, add to digester2 & parse, etc.

However I doubt that reusing them while a parse is still in progress
will work without significant rework of Digester core functionality.



You would also never be able to use digester1 again in this case, because the rules instances have been swiped.

The exception you are getting is caused by some Rule object throwing an
exception in its end method, which fits with what I would expect to
happen if you change the Digester a rule is associated with between
calls to begin() and end() [because you added the rule to a different
Digester object].

Regards,

Simon


Craig




[EDS] - Problems parsing main config file: : com.circuitcity.eds.exceptions.XmlParseException: com. circuitcity.eds.exceptions.XmlParseException: com.circuitcity.eds.exceptions.XmlParseException: java .lang.NullPointerException
at org.apache.commons.digester.Digester.createSAXException(Digester.java:2540)
at org.apache.commons.digester.Digester.createSAXException(Digester.java:2566)
at org.apache.commons.digester.Digester.endElement(Digester.java:1061)
at org.apache.xerces.parsers.SAXParser.endElement(SAXParser.java:1403)
at org.apache.xerces.validators.common.XMLValidator.callEndElement(XMLValidator.java:1550)
at org.apache.xerces.framework.XMLDocumentScanner.scanElement(XMLDocumentScanner.java:1809)
at org.apache.xerces.framework.XMLDocumentScanner$ContentDispatcher.dispatch(XMLDocumentScan
ner.java:1182)
at org.apache.xerces.framework.XMLDocumentScanner.parseSome(XMLDocumentScanner.java:381)
at org.apache.xerces.framework.XMLParser.parse(XMLParser.java:1098)
at org.apache.commons.digester.Digester.parse(Digester.java:1567)

Thanks for your support.
-Robert Grey



From: Simon Kitching <[EMAIL PROTECTED]>
Reply-To: "Jakarta Commons Users List" <[EMAIL PROTECTED]>
To: Jakarta Commons Users List <[EMAIL PROTECTED]>
Subject: Re: [digester] Multiple Digester Instances
Date: Wed, 15 Oct 2003 09:25:27 +1300

Hi Robert,

The "xmlrules" code currently does this sort of thing, so you may wish
to look there for inspiration.

It would also help if you included the stack trace for your "null
pointer" problems.

One thing I notice in your code snippet below: where does the "rules"
object you are passing to your new Digester instance come from? If it is
the value returned by digester.getRules(), then this may be the cause of
the problem; I doubt that the same Rules object can be used in multiple
Digester instances.

Regards,

Simon

On Wed, 2003-10-15 at 09:10, Robert Grey wrote:


Currently I am using digester recursively, I have an object that will
create a new instance of digester when it is called from a rule in a
previous digester instance. I continually get null pointers when I try

to do


this with this code:

public void parseMainConfigFile(InputStream stream) throws

GeneralException


{
   // now that plugins are configured, start the parsing process
   try {
       //return (ParseMainXml) digester.parse(stream);
       Digester newDigester = new Digester();
       newDigester.setValidating(false);
       newDigester.addObjectCreate(ROOTNODE, ParseMainXml.class);
       newDigester.setRules(rules);
       newDigester.parse(stream);
    } catch (Exception e) {
       throw new XmlParseException(e);
    }
}

This method is used to create the original parser and to parse documents
called from that original parser. Is there any way to do this properly?
Thanks for any advice...
-Robert Grey



---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]



_________________________________________________________________
Never get a busy signal because you are always connected with high-speed Internet access. Click here to comparison-shop providers. https://broadband.msn.com


---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]






---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]





---------------------------------------------------------------------
To unsubscribe, e-mail: [EMAIL PROTECTED]
For additional commands, e-mail: [EMAIL PROTECTED]

Reply via email to