On 31.01.2006 13:19:50 Rolf Bruderer wrote:
Jeremias Maerki dev at jeremias-maerki.ch writes:
See http://xmlgraphics.apache.org/fop/0.20.5/graphics.html#caching on
how to reset the image cache in FOP 0.20.5 between rendering runs. Note
that this function is not available anymore in the latest version since
there the cache works differently. It has much better memory reclaiming
abilities (using weak references) so a cache reset method should not
be necessary if you use unique URLs.
Hi
Thank you very much for the fast answer and your advice how to reset
the cache. That was very helpfull.
Anyway I have to say, that I think that this static image cache is
not such a good solution (even not with weak references).
I'm sure you can come up with suggestions for a much better image cache.
We'd love to apply patches in that direction. Anyway, we plan to add an
environmental class that will hold configuration information that
doesn't change between rendering runs. When this is available I want to
attach the existing image cache to that environmental class. That will
make the image cache less static.
so a cache reset method should not be necessary if you use unique URLs.
Caching only with respect to the urls without considering if the url
content has changed inbetween (e.g. modification date) seems not very
proper to me.
As I said above, we're looking forward to any patches that improve the
current situation.
If done so, the user should at least have a chance to decide whether to
bypass this cache or to empty it. If I understood you right, in the latest
version it is not even possible anymore to empty the cache?
No, not at the moment.
On the other side, if anyone submits a patch to retrofit this method
we will surely consider adding it.
If you give me some hint how to access the cache and if I find some time
I would try to do it. But for the moment I think that I simply stick
to the older version.
Look into org.apache.fop.images.ImageFactory. It should be very easy to
do.
However, I'd prefer an extension attribute on fo:external-graphic
that signals FOP to bypass the image cache entirely.
I don't think that changing the fo:external-graphic specification to the
needs of FOP is something that is in your power or is it?
I don't agree that this attribute would be a good solution. Since a
writer of a FO-file usualy does not want to concern about cache bypassing.
FOP should better use the correct (cached or reloaded) picture in any case.
I'm not suggesting altering the FO specs. I'm suggesting an proprietary
extension
(!) attribute. Something like:
fo:external-graphic src=http://localhost/MyImageServlet;
fox:bypass-cache=true/
(where fox is xmlns:fox=http://xmlgraphics.apache.org/fop/extensions;)
Usually, the stylesheet-writer knows that an image is not cacheable so
this is actually quite feasible. If you have a better approach that does
not cost a lot of performance because of network roundtrips then I'm all
for it. Another idea could be to add a user-configurable list of URL
patterns that will not be cached by FOP. Also very easy to do.
Those are just my thoughts about it. In any case I am very thankful for your
help and I appreciate your work. Thank you very much.
You're welcome. I'm looking forward to your suggestions and patches.
Jeremias Maerki
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