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From Michael Rubin <mru...@thunderhead.com>
Subject Re: Event broadcasting and listening question
Date Fri, 13 May 2011 15:06:56 GMT
Thanks for your reply. I have now added the getter and setter to 
PDFDocument as shown below and added 'this.pdfDoc.setEventListener(new 
PDFLibraryEventAdapter(getUserAgent().getEventBroadcaster());' to 
PDFDocumentHandler.startDocument() (last line inside the try block). Now 
I can get the listener from the PDFEncryptionJCE class. However what do 
I do with it? And how does this relate to the producer class and the 
EventBroadcaster that I am trying to get hold of?

In your first reply you said to create the Listener and Producer 
interfaces. Based on the FontEvent* classes, both of these had an event 
definition for their events. But in the latest reply you are saying not 
to put my event in the new PDFEventListener? That would make it an empty 
interface then if I understand right. So what would its purpose be? I 
can't seem to do anything with it.

Following discussion with a colleague (Vincent) I left the listener 
method in (but without the source) and made the call to that to kick off 
the event. However now I get an InvocationTargetException when I try to 
get the PDF Doc in order to invoke the listener event method. Looking at 
the stack trace it happens when I call the 
PDFDocument.getDocumentSafely() method. It seems when debugging to be 
PDFEncryptionManager.newInstance() where the error is occurring, the 3rd 
line calling makeMethod.invoke(...). (I attempted to run the build ant 
script and then refresh eclipse but this didn't make any difference.)

I will continue with this on Monday. Any further pointers in the 
meantime very much appreciated.

There are two questions that come from my colleague:

1. What is the source object for? And do we need it referenced in the 
Listener? Or just the producer?
2. Why should we get the PDFDocument object from the Encryption class? 
Should the listener not be passed into the Encryption class via its 
constructor rather than having to go fetch the listener?

Thanks!

-Mike


On 12/05/11 21:29, Jeremias Maerki wrote:
> On 12.05.2011 10:44:41 Michael Rubin wrote:
>> Thanks a lot for your response Jeremias. I have now done the following:
>>
>> - Added 'void warnRevision3PermissionsIgnored(Object source);' (and its javadoc)
to PDFEventProducer in the org.apache.fop.render.pdf package and added a corresponding entry
to the xml. Removed the org.apache.fop.pdf.PDFEventProducer class and xml.
>> - Created org.apache.fop.pdf.PDFEventListener interface containing just 'void warnRevision3PermissionsIgnored(Object
source);'.
>> - Created PDFLibraryEventAdaptor in the org.apache.fop.render.pdf package that extends
the PDFEventListener. (Currently just contains my new event. Should I also add the existing
2 render.pdf events to this class?)
> Or do it the other way around: add your new event to PDFEventProcuder.
> Doesn't make sense to have two.
>>    I can also see how to obtain the PDFDocument object from the
>> PDFEncryptionJCE class via the getDocumentSafely() method. But I am not sure how
to get the event broadcaster from that object. How is this done?
> public class PDFDocument {
>
> [..]
>
>      private PDFEventListener listener;
>
> [..]
>
>      public void setListener(PDFEventListener listener) {
>          this.listener = listener;
>      }
>
>      PDFEventListener getListener() {
>          return this.listener;
>      }
> [..]
>
> That's the simples way and should probably be sufficient. If we wanted
> to get fancy, we could handle a List<PDFEventListener>.
>
> In PDFDocumentHandler.startDocument():
> this.pdfDoc.setEventListener(new PDFLibraryEventAdapter(getUserAgent().getEventBroadcaster());
>
> So, the PDFDocument doesn't actually get an EventBroadcaster.
> PDFDocument calls the PDFLibraryEventAdapter and that one in turn calls
> the EventBroadcaster. Nicely decoupled.
>
>
>> Thanks!
>>
>> -Mike
>>
>>
>> On 11/05/11 19:46, Jeremias Maerki wrote:
>>> 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.
>>>
>>> HTH
>>>
>>> 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
>>>>
>>>> The contents of this e-mail are intended for the named addressee only. It
contains information that may be confidential. Unless you are the named addressee or an authorized
designee, you may not copy or use it, or disclose it to anyone else. If you received it in
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>>>> immediately and then destroy it.
>>>>
>>>>
>>>>
>>>>
>>>
>>> Jeremias Maerki
>>>
>
>
> Jeremias Maerki
>


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