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From Jeremias Maerki <...@jeremias-maerki.ch>
Subject Re: generating data url external-graphic in PDF
Date Wed, 08 Feb 2006 22:47:59 GMT
The protocol handler is a plug-in for a very low-level service in the
Java class library. It plug directly into the java.net.URL subsystem.
That's why these classes must be available on a very low level.

If you want to know more about protocol handlers, read:
http://java.sun.com/developer/onlineTraining/protocolhandlers/

Yes, I'm sure your modified classes get called, but they get called in
the context of a special class loader that's set up specifially for your
web application. The java.net.* stuff however, is a basic class library
service so these classes won't see the protocol handler if it's not
added to the system class loader.

Here are a couple of links that may help:
http://www.developer.com/java/other/article.php/10936_2248831_1
http://www.theserverside.com/articles/article.tss?l=ClassLoading

On 08.02.2006 23:16:05 Edward McMasters wrote:
> I am still trying to figure out how to do what you
> suggested, but meanwhile, sorry to belabor this point,
> but, what is special about this protocol handler?  I
> was able to replace other classes
> (org.apache.fop.render.pdf.PDFRenderer,
> org.apache.fop.fo.flow.ExternalGraphic) that are
> called from inside the FOP JAR to my modified class in
> WEB-INF/classes and my local versions get called by
> FOP (as evidenced by System.out displays).
> 
> Thanks.
> 
> Edward (confused but slowly trying to learn!)
> 
> --- Jeremias Maerki <dev@jeremias-maerki.ch> wrote:
> 
> > In addition to what Chris already told you: Maybe I
> > was not clear enough.
> > You don't place that JAR file with the protocol
> > handler with your other
> > JARs (i.e. not in WEB-INF/lib), you need to place it
> > in WebSphere so
> > they end up in the top-level class loader. That
> > directory could be a
> > "lib" directory directly under the root where you
> > installed WebSphere.
> > As I said, you will need to consult the WebSphere
> > documentation to find
> > the right spot. What I forgot to mention is that in
> > addition to the JAR
> > file with the protocol handler you will need to
> > place the batik.jar in
> > the same place, too, because the protocol handler
> > references classes
> > from batik.jar.
> > 
> > On 08.02.2006 17:58:53 Edward McMasters wrote:
> > > I generated a JAR with just those classes and put
> > it
> > > in the same place as my other JAR files, giving
> > this
> > > new one precedence and got the same result.  I am
> > in
> > > the middle of attempting to try rebuilding FOP
> > 0.20.5
> > > with these new classes embedded but I am currently
> > > having a problem because it seems that I cannot
> > get
> > > one of the packages from the source download
> > > (org.apache.fop.fo.properties).
> > > 
> > > Should I be concerned that the package
> > > org.apache.fop.util.protocols.data does not appear
> > in
> > > the original FOP 0.20.5 JAR?  I am just wondering
> > > where these classes will be called from, although
> > the
> > > program that I copied has the same libraries as my
> > > program and it has no trouble referencing these
> > > classes.
> > <snip/>
> > 
> > 
> > Jeremias Maerki
> > 
> > 
> >
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> > 
> 
> 
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Jeremias Maerki


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