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From Hans Gilde <>
Subject RE: [Jelly] nested compileScript() with import ?
Date Mon, 06 Dec 2004 01:20:42 GMT
Ok, it sounds reasonable to want those caching conditions. But for my own
curiosity, why do you want them? Are you in a tight memory situation or is
it a perfectionist thing?

What's wrong with using JellyContext variables? It's pretty much what
they're there for.

You can think of a JellyContext as a scope. At each level of XML tag, you
get a new JellyContext (a new scope). Export says "when a variable is set
into the current scope, should I automatically put it into the scope above"?
Inherit says "when creating a new scope, should I give it all the variables
from the current scope"?

If a Tag wants to set a variable in a context (scope) that's higher up in
the tree, there are two choices: use export=true or find the parent context
(while ((parent = getParent()) != null)).

To find a variable that's been set into a context above yours, either use
inherit=true or findVariable.

I'd suggest this solution:

Have your Tag find the top level context (while ((parent = getParent()) !=
null)). Use a single variable name in this context, say my_imported_scripts.
That variable will be a single HashMap from uri to parsed Script instance.

As you saw, compilable tags are sort of compiled, but they don't get a
context or their attributes at that point. The problem with compilable tags
(I don't recommend using them) is that they're only compiled with respect to
the thread that compiles them. If you run the same Script in a different
thread, those compiled tags won't be there. This is not true for a Script.
Once a Script is compiled, it stays compiled no matter where you use it.


-----Original Message-----
From: Arnaud Masson [] 
Sent: Sunday, December 05, 2004 5:06 PM
To: Jakarta Commons Users List
Subject: Re: [Jelly] nested compileScript() with import ?

Yes,  I have copied the import tag and added the cache to the new tag.
It works fine, but I would like to reuse compiled scripts
- if several container scripts include the same sub script
- if a container script include the same sub script several times

To do that, I currently use the JellyContext to cache compiled scripts 
with a call to setVariable(),
using a variable name based on the script uri... it works, but it's not 
really clean.

Maybe a better way would be to override the compileScript() methods of 
the JellyContext
and add a cache of compiled scripts inside the context (indexed by 
uri/url) ?

Also I am not sure how to handle the 'export' and 'inherit' parameters 
when I use compileScript+run instead of a single call to runScript().

You say a Tag isn't compilable, but what's the "CompilableTag" ??
I tried to use it the but the attributes (uri,...) of my tag are empty 
when "compile" is called.

Thanks for your help!

.Hans Gilde wrote:

>You could easily cache the imported script the first time it's run. This is
>a simple modification to the current import tag, so that it keeps the
>reference to the script. If you do this, why not add an attribute "cache"
>turn caching on/off and then submit it as a patch to the import tag?
>It would be a little harder, but not at all impossible, to make it cache
>imported script at compile time.
>If not, the basic idea is this:
>A Tag isn't compilable, it's generated at runtime. A Script is compilable,
>it's generated at compile time. You need a special Script, not a special
>Tag. Scripts are very much like tags except that they need to be thread
>safe. Most of the time, a Script called TagScript is used. By default, this
>Script creates and caches Tag instances when it's run.
>Your new Script would compile the import at compile time. The result of
>compiling the import is, it self, a Script instance. At runtime, your
>would simply pass control to the imported Script.
>You would also have to implement a custom TagLibrary. A TagLibrary gets to
>create a TagScript (implements Script) for every XML tag in its namespace.
>So, your TagLibrary would create a custom TagScript that would compile and
>keep the imported XML.
>-----Original Message-----
>From: Arnaud Masson [] 
>Sent: Saturday, December 04, 2004 6:07 PM
>Subject: [Jelly] nested compileScript() with import ?
>in the current version of jelly "import" tag, it seems that imported 
>scripts are always parsed and recompiled each time the containing script 
>even if this script has already been compiled.
>the problem is that  it isn't optimized if the compiled version of the 
>main script is cached.
>is it possible to compile all scripts included via <j:import ...> via a 
>single call to jellyContext.compileScript() on the containing script ?
>should i write a custom tag to implement that (to replace import) ?
>thanks in advance
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