commons-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Craig R. McClanahan" <craig...@apache.org>
Subject Re: [digester] Multiple Digester Instances
Date Tue, 14 Oct 2003 22:14:26 GMT
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 <simon@ecnetwork.co.nz>
>>>Reply-To: "Jakarta Commons Users List" <commons-user@jakarta.apache.org>
>>>To: Jakarta Commons Users List <commons-user@jakarta.apache.org>
>>>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: commons-user-unsubscribe@jakarta.apache.org
>>>For additional commands, e-mail: commons-user-help@jakarta.apache.org
>>>
>>>      
>>>
>>_________________________________________________________________
>>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: commons-user-unsubscribe@jakarta.apache.org
>>For additional commands, e-mail: commons-user-help@jakarta.apache.org
>>
>>
>>    
>>
>
>
>---------------------------------------------------------------------
>To unsubscribe, e-mail: commons-user-unsubscribe@jakarta.apache.org
>For additional commands, e-mail: commons-user-help@jakarta.apache.org
>  
>



---------------------------------------------------------------------
To unsubscribe, e-mail: commons-user-unsubscribe@jakarta.apache.org
For additional commands, e-mail: commons-user-help@jakarta.apache.org


Mime
View raw message