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From "Christian Kurz" <crk...@gmx.de>
Subject Re: ServerPageAction: XMLFragment reuse in XSL transformer
Date Sat, 19 Oct 2002 09:53:26 GMT
I'll try to implement a pipeline similar to this:

FileGenerator        -> "MyFilterTransformer" -> other steps

The FileGenerator will read the big document and is cacheable.
MyFilterTransformer will use the XMLFragment from the session to forward only a small portion
of the events from the generator, following your idea. MyFilterTransformer is the first component
in the pipeline, which is NOT cacheable, as it returns different data on every request.

To my understanding cocoon's caching strategy should cache the pipeline as far as possible.
In this particular case only including the FileGenerator:

"The keys of all cacheable components are chained, and together they build the cache key.
The request is processed, and the document is built. The cache stores the result of the _last_
component, indicating cacheablility. The next time this document is requested, the key is
built, and the cached content is fetched from the cache.

Next, the cache asks all components of the event pipeline, if their input has changed since
the time the content was cached. For example, the generator checks this by looking at the
last modification date of the xml document, the xslt transformer checks the date of the stylesheet,
and so on. Only if all state that the content is still valid it is used from the cache. Otherwise,
the document is generated from scratch. So the event pipeline tries to cache as much of the
XML processing pipeline as possible."
from New Riders, Cocoon: Building XML Applications by Matthew Langham and Carsten Ziegeler,
p. 182.

  ----- Original Message ----- 
  From: Hunsberger, Peter 
  To: 'cocoon-users@xml.apache.org' 
  Sent: Friday, October 18, 2002 4:23 PM
  Subject: RE: ServerPageAction: XMLFragment reuse in XSL transformer


  Well, obviously, it something changes on every request then, by definition, it isn't cacheable.
 However, I believe, with aggregation, only the components that are marked as invalidated
in the cache are rebuilt on a new request; the rest of the data stays in it's respective cache.
  This does mean that the aggregated document is rebuilt each time (I have no idea what the
impact of that would be).  But the "large" document source would stay not be retrieved from
scratch.

  Perhaps using the document function as Olivier would avoid this.  At one point document
did not check cache validity at all and you would only get a newer version of the data if
the main data was invalidated in cache. I think this has been fixed in 2.0.3.  The problem
is how to get the URI resolve for the document function to fund the data in session.  Someone
else will have to tell you how to do that (and if it's even possible)...

   -----Original Message-----
  From: Christian Kurz [mailto:crkurz@gmx.de]
  Sent: Friday, October 18, 2002 1:42 AM
  To: cocoon-users@xml.apache.org
  Subject: Re: ServerPageAction: XMLFragment reuse in XSL transformer


    Thank you very much for the quick feed-back! The idea sounds great and is a lot cleaner,
than fiddling something in some XSL extension.

    I am not sure about the cachaebility: the XMLFragment specifying, which nodes to filter
from the big input document, changes everytime, so Cocoon would need to parse the source file
on every request (, if my understanding is right).

    If I'd slidely change your approach to implementing the same approach into a transformer
component. This transformer component will not be cacheable, but at least the generator in
front of it would be.

    Thanks again,
    Christian


    BTW, thanks also for the code snippet. It helps a lot, as soon as it comes to thinks like
the ObjectModel, I start feeling uncomfortable.

    ----- Original Message ----- 
      From: Hunsberger, Peter 
      To: 'cocoon-users@xml.apache.org' 
      Sent: Thursday, October 17, 2002 6:46 PM
      Subject: RE: ServerPageAction: XMLFragment reuse in XSL transformer


      There's probably about half a dozen ways to do this.  Perhaps one of the simplest is
just to create your own caching generator and use aggregation (with any other XML you may
need) in the pipeline.

      In the generator you'll need to implement the setup method to see the objectModel, something
like the following:

      private gunk mySessionData = null;

      public void setup( SourceResolver resolver, Map objectModel, String src, Parameters
parms )
            throws ProcessingException,  SAXException,   IOException
         {
           if (mySessionData == null ) {
                super.setup( resolver, objectModel, src, parms );
                Request request = (Request)ObjectModelHelper.getRequest(objectModel);
                Session session = request.getSession(false);
                if (session != null)  {
                  // save a pointer to your session data for use in the generate method
                  mySessionData = ....
               }
            }
         }   

      Now in your generate method just pick up whatever data hangs off of "mySessionData"
and away you go

      -----Original Message-----
      From: Christian Kurz [mailto:crkurz@gmx.de]
      Sent: Thursday, October 17, 2002 11:26 AM
      To: cocoon-users@xml.apache.org
      Subject: ServerPageAction: XMLFragment reuse in XSL transformer

      Hello cocoon-users,

        I need to generate some tiny XML elements (XMLFragment) within a ServerPageAction
and I would like to use this XMLFragment later on in an XSL transformer, that is fed by an
xml generator. The XMLFragment captured in the ServerPageAction is basically saying, which
nodes are to be returned from the big input document.

        From some other message in this group I have understood, that passing objects is only
possible through session or request objects, but not through sitemap variables. I don't like
to use a request generator as the starting point of the pipeline, as I'd loose cacheability
at a very early step in the pipeline. With a quite big xml input document, this does not seem
a good idea to me.

        So I am currently struggling how to get a piece of XML, that is attached to a session
or request object, into the xsl transformer. Has anybody tried this before e.g. using an XSL
extension?

        Any help or hints appreciated!

        Thank you in advance,
        Christian

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