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Re: [FreeMarker-user] Removing templates manually from a cache.

Daniel Dekany

2011-12-15

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Wednesday, December 14, 2011, 11:52:35 PM, Frank Zeyda wrote:

> Dear FreeMarker Developers,
>
> Here's a small problem I encountered when using a MultiTemplateLoader that
> first loads templates from the file store, and via a second
> StringTemplateLoader allows for creation and use of on-the-fly templates while
> the program executes. The reason for using a common loader is
> intentional so that the on-the-fly templates can include those from the
> file store where needed.
>
> My problem is that I reuse the same name for the on-the-fly templates when
> inserting them i.e. using the StringTemplateLoader method (putTemplate(...)).
> This does not seem to cause the template to be reloaded unless one clears the
> entire cache using clearTemplateCache() of the TemplateCache object. This,
> however, appears to be inefficient as I suppose it would cause all templates
> previously cached to be reloaded.

It would.

> setDelay() is not much use since I need the one template to be
> reloaded immediately.

BTW the whole delay business has a design issue... it should be
per-template-loader. After all, what the ideal delay depends on how
resource consuming checking if the source was changed is. So, I just
wonder of a 0 delay for the StringTemplateLoader and non-0 for the
FileTemplateLoader would solve your problem. Anyway, you can't do
that...

> To solve the problem, I tried to create and
> set my own CacheStore, however, the methods get(...), put(...) and
> remove(...) are of not much use here since one has no public access
> to the object that is used as the key in the underlying map
> (TemplateCache.TemplateKey is private).

You are supposed use the CacheStorage API only indirectly, trough the
Configuration API. Or at least I suppose that was the intent of the
authors. Problem is, there's nothing that calls CacheStorage.remove in
FreeMarker, as far as I see at least. (Consequently, that method of
CacheStorage implementations isn't field tested... But I don't know
the author of them as sloppy, so let's hope for the best.)

> So, to summarise, the solution to the above problem via clearTemplateCache()
> seems to be not entirely satisfactory. Instead one may wish to have finer
> control about the caches, for instance, in order to remove specific entries
> manually; possibly via a method in TemplateCache, or by way of exposing
> TemplateCache.TemplateKey so that keys can be created by the user.

Can you get the TemplateCache instance at all? There's no
Configuration.getTemplateCache, nor setTemplateCache. I think the only
reason TemplateCache is public is that access control in Java is
overly simplistic for any product that has sub-packages.

Anyway... I have added Configuration.removeTemlateFromCache to the 2.3
branch. Tell me if it works. Here's the build:
http://freemarker.org:8085/download/FM-BRANCH23/artifacts/build-266/Library/freemarker.jar

> Many thanks for any comments, in particular in case I am missing a simpler
> solution.
>
> Best wishes
> Frank
>
>

--
Best regards,
Daniel Dekany


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