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From Craig McClanahan <>
Subject Re: [chain] add expression evaluation?
Date Thu, 02 Dec 2004 23:08:29 GMT
Interestingly, Digester already supports the expression replacement
mechanics (see org.apache.commons.digester.Substitutor), so it ought
to be really easy to do this kind of thing, and an elegant solution to

I'm +1 for it.


On Thu, 2 Dec 2004 16:40:31 -0600, Joe Germuska <> wrote:
> In a discussion on the struts-user list, I got around to describing a
> configuration format which made me wonder if folks would tolerate
> some kind of expression evaluation engine in chain.
> The musing repeated below:
> At 1:57 PM -0600 12/2/04, Joe Germuska wrote:
> >I think you could find the view processor command by using the
> >standard Chain "lookup action".  Well, out of the box, its "nameKey"
> >property would depend on some String value being placed into the
> >context under a certain key, and as it is now, we're talking about
> >using a String property of an Object in the context under a certain
> >key.  If we gave the LookupCommand an expression language (JEXL,
> >perhaps?), then we could do something like this, which seems cool:
> >
> >       <command
> >           className="org.apache.commons.chain.generic.LookupCommand"
> >         catalogName="struts-view-preprocess"
> >                nameKey="${}"
> >            optional="true"/>
> >
> >or possibly work some magic to make the "context" prefix assumed.
> >Anyone  have an opinion about adding a JEXL dependency to Chain, or
> >whether this would be best left to a Struts subclass of
> >LookupCommand?
> Ideas?  I'm not sure right now of the scope of this proposal -- is it
> just for the LookupCommand?  Is it somehow implemented more widely?
> How can you do that when Chain is first-and-foremost an API?
> I can certainly see some of these questions leading folks to throw up
> their hands and say "let's just keep it simple."  There's no critical
> reason to add this dependency to the core, but when you think about
> the expressive power it would provide in the config files, it seems
> pretty cool.
> Joe
> --
> Joe Germuska
> "Narrow minds are weapons made for mass destruction"  -The Ex
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