On Wed, 2007-07-25 at 11:58 +0530, Soumya Chatterjee wrote:
>
> Hi Michael,
>
> Do you think SAX is a good alternative for the DOM in this case. We
> can migrate the parsing mechanism to SAX if there is no thread safe
> issue in SAX parser.
SAX will help you build custom Data model for the XML it is parsing.
Usually SAX parsing of XML file is done only once (inside a method) to
construct the Data model. It is *not* a good idea to start a SAX parser
every time you would like to read something from the XML. (if thats what
you were hinting at in your question above)
You could think of DOM as a "generic" Data model that works for all
XMLs. While using DOM every thing is a Node/Element/Text Node and you
lose out on type safety and domain friendliness a custom Data model
would offer.
Consider the proverbial purchase order xml[1] for example:
You could walk this XML with SAX parser and construct Data model like
Class PurchaseOrder {
Address getShippingAddress();
Address getBillingAddress();
List<Item> getItemsOrdered();
String getComment();
} //Notice there are not setters
Where if you were to make DOM of the same XML, you would have to walk
NodeList list = purchaseOrderNode.getChildNodes(); //This is not thread
safe
Now is it a good alternative to DOM ?
The answer would depend as always on your use-cases. An immutable Data
object is as thread safe as it can get. And if you are accesses to XML
are read only, constructing a Data model from SAX parsing is worth
considering.
Hope this helps
-Prashant
[1] : http://www.w3.org/TR/xmlschema-0/#po.xml
PS: While you are at exploring options, you could also give JAXB a look
see.
> Thanks,
> Soumya Chatterjee
> Tata Consultancy Services
> Mailto: [EMAIL PROTECTED]
> Website: http://www.tcs.com
> ____________________________________________
> Experience certainty. IT Services
> Business Solutions
> Outsourcing
> ____________________________________________
>
>
> Michael Glavassevich
> <[EMAIL PROTECTED]>
>
> 07/24/2007 07:27 PM
>
>
> To
> Soumya Chatterjee
> <[EMAIL PROTECTED]>
> cc
> j-users@xerces.apache.org
> Subject
> Re: Got the Issue
>
>
>
>
>
>
>
>
> Hi Soumya,
>
> Xerces' DOM implementation isn't thread-safe. If you try to access
> the
> same DOM instance from multiple threads without synchronizing it
> you'll
> run into these problems. You either need to synchronize your code or
> create an instance of the DOM tree per thread. There's really no way
> around it.
>
> Thanks.
>
> Michael Glavassevich
> XML Parser Development
> IBM Toronto Lab
> E-mail: [EMAIL PROTECTED]
> E-mail: [EMAIL PROTECTED]
>
> Soumya Chatterjee <[EMAIL PROTECTED]> wrote on 07/24/2007
> 09:42:08
> AM:
>
> > Hi Michael,
> >
> > I found out the response from you regarding the "xerces DOM
> > concurrent access" and I think it is the same as our application in
> > the case. http://spteam-lists.blogspot.com/2007/04/re-xerces-dom-
> > concurrent-access-and.html
> >
> > By the way we were not getting the exception as frequently in the
> > weblogic 7.1 ( JDK 1.3) when we are using the following Xerces.
> >
> > But we are getting the exception in case of weblogic 9.1 much more
> > frequently which uses JDK1.5 and different version of Xerces.
> >
> > Synchronization is not an option in this case because there is a
> > huge performance issue here. Please let me know if any way we can
> > get read of this problem without using the Synchronization block.
> >
> > Thanks,
> > Soumya Chatterjee
> > Tata Consultancy Services
> > Mailto: [EMAIL PROTECTED]
> > Website: http://www.tcs.com
> > ____________________________________________
> > Experience certainty. IT Services
> > Business Solutions
> > Outsourcing
> > ____________________________________________
>
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--
-Prashant
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