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From Jeremias Maerki <...@jeremias-maerki.ch>
Subject Re: Event broadcasting and listening question
Date Wed, 11 May 2011 18:46:22 GMT
Hi Michael

Creating a new EventBroadcaster is obviously wrong. The idea is that the
user can get events for each FOP rendering run separately (unlike
logging where concurrent runs get mixed up). So you have to get hold of
that EventBroadcaster applicable to the current rendering run. Obviously,
you don't have access to the FOUserAgent in the PDF library. That is
intentional because the PDF library should remain reasonably independent
of as much FOP code as possible for the case that we ever factor it out
into a separate component/module or move it to XML Graphics Commons.

My suggestion is to follow a similar path as done in
org.apache.fop.fonts: Create an interface for the events coming out of
the PDF library (see FontEventListener). Let's call it PDFEventListener
or something like that and put it in the org.apache.fop.pdf package.
Then move your PDFEventProducer (corresponds to FontEventProducer) into
org.apache.fop.render.pdf as this package makes the glue between FOP and
PDF output. Then create a PDFLibraryEventAdapter (implements PDFEventListener)
in the org.apache.fop.render.pdf package (corresponds to
FontEventAdapter). The PDFLibraryEventAdapter will get the
EventBroadcaster from the PDFDocumentHandler which is responsible for
instantiating the PDFDocument and PDFLibraryEventAdapter. The adapter is
then added as listener to a List<PDFEventListener> that you can add to
PDFDocument. From PDFEncryptionJCE you should have access to the
PDFDocument via the getDocumentSafely() method. That nicely decouples
FOP's event subsystem from the PDF library.


On 11.05.2011 15:47:49 Michael Rubin wrote:
> ?Hello there. I have been busy implementing 128 bit PDF encryption for FOP. I have already
got it working successfully but one issue remains that I have a question about.
> In the org.apache.fop.pdf.PDFEncriptionJCE.init() method there is one place where I want
to broadcast an event message. I looked athttp://xmlgraphics.apache.org/fop/trunk/events.html
 to learn about events. However it just shows "EventBroadcaster broadcaster = [get it from
somewhere];" and doesn't show how I should be getting the broadcaster. After looking in the
code in the AFP package for existing examples I put together the following which seems to
work on testing:
> FopFactory fopFactory = FopFactory.newInstance();
> FOUserAgent agent = fopFactory.newFOUserAgent();
> EventBroadcaster eventBroadcaster = agent.getEventBroadcaster();
> PDFEventProducer eventProducer = PDFEventProducer.Provider.get(eventBroadcaster);
> eventProducer.warnRevision3PermissionsIgnored(this);
> This creates a new FopFactory, from which I create a new FOUserAgent, from which I can
get the event broadcaster to supply to my event producer. (I had to create a PDFEventProducer
which extends EventProducer. Plus PDFEventProducer.xml which contains the message mapping.)
> In this case the EventBroadcaster will be created new every time so I am not sure existing
listeners will pick up. So is there a recommended way that I can get an existing event broadcaster
to use? Or is the above way the correct way to do it after all?
> Version of FOP is v1.0. Platform is Ubuntu Linux, running from within the Eclipse IDE.
> Thanks!
> -Mike
> Michael Rubin
> Developer
> T: +44 20 8238 7400
> F: +44 20 8238 7401
> mrubin@Thunderhead.com
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Jeremias Maerki

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