I was driving up this morning (Silicon Valley commute) thinking about
this. Maybe we could call it VSTL (Velocity Standard Tag Library)?
New implementation idea... use a custom Context object that serves as
an adapter to the PageContext. This way you wouldn't need to
populate a Context ahead of time. Whenever an object is needed, it is
just pulled directly from the page/request/session PageContext. (same
as JSTL).
Similarly, <v:set> would store the object in the PageContext (is
request scope the default for JSTL?) with an optional scope parameter
to put it in one of the other scopes.
We should really make a Wiki page about this...
WILL
On 8/20/06, Will Glass-Husain <[EMAIL PROTECTED]> wrote:
Incidentally, why stop at <v:set>? I'd also expect to see <v:if>,
<v:choose>/<v:when> (for if/then/else), <v:out>.
One big advantage of Velocity over JSTL is the ability to easily
create macros. Defining a macro <v:macro> at the top of the page then
using it below would be quite nice. It'd be trickier to implement
though. The above tags could all execute stand-alone VTL, but
<v:macro> would need to have some kind of connection with the tags
later in the page.
WILL
On 8/20/06, Will Glass-Husain <[EMAIL PROTECTED]> wrote:
> Hi Jeff,
>
> Now I get it. If you built a simpler tag that always stored a String
> object this would be easy-- just use Velocity.evaluate as I suggest.
> But you want to evaluate an expression to a resulting object.
>
> Seems to me that you want this to act similar to the Velocity #set.
> You might start by looking at the class
> o.a.v.runtime.parser.node.ASTSetDirective. The key line is:
>
> Object value = right.value(context);
>
> which evaluates the right hand side of the #set expression.
>
> One way of approaching this is to consider that Velocity.evaluate()
> basically ends up calling Node.render() which is a recursive series of
> parser nodes that output to a Writer. You need a similar starting
> point to call Node.value() which will recursively evaluate an
> expression.
>
> Just a few quick thoughts, hope they point you in a useful direction...
>
> WILL
>
> On 8/19/06, Jeff Schnitzer <[EMAIL PROTECTED]> wrote:
> > I'm just evaluating Velocity expressions. The result of the expression
> > should be an object, whereas Velocity.evaluate() renders output to a
> > Writer as text. The method I'm looking for would look something like this:
> >
> > public Object evaluate(Context ctx, String expression);
> >
> > For example:
> >
> > ctx.put("now", Calendar.getInstance());
> > TimeZone tz = (TimeZone)evaluate(ctx, "now.timeZone");
> >
> > The Introspector seems to be much, much lower level than this.
> >
> > Thanks,
> > Jeff
> >
> > Will Glass-Husain wrote:
> > > Not sure I get it. Are you making a new expression language or just
> > > evaluating Velocity expressions?
> > >
> > > The introspector is what resolves objects and methods in Velocity.
> > >
> > > WILL
> > >
> > > On 8/19/06, Jeff Schnitzer <[EMAIL PROTECTED]> wrote:
> > >> Velocity.evaluate() renders textual output to a Writer. For the
> > >> expression language to work, I need to resolve objects. I can't find
> > >> anything in the javadocs that might give me a hook.
> > >>
> > >> Any suggestions?
> > >>
> > >> I know, I need to wade through the code, but a few starting pointers
> > >> would help.
> > >>
> > >> Thanks,
> > >> Jeff
> > >>
> > >>
> > >> Will Glass-Husain wrote:
> > >> > Wow! As a both a Velocity enthusiast and JSTL junkie that sounds like
> > >> > a really useful tag.
> > >> >
> > >> > It doesn't sound that hard to me. Extract the expression, call
> > >> > Velocity.evaluate, and set the request attribute. I guess you'd have
> > >> > to set up the context with all the beans first.
> > >> >
> > >> > WILL
> > >> >
> > >> >
> > >> > On 8/17/06, Jeff Schnitzer <[EMAIL PROTECTED]> wrote:
> > >> >> Short version: I wish for a JSP custom tag that will effectively
> > >> let me
> > >> >> use Velocity expressions instead of the anemic JSTL expressions.
> > >> >>
> > >> >> Long version:
> > >> >>
> > >> >> Velocity already has a custom JSP tag that lets me do this:
> > >> >>
> > >> >> <vel:velocity>
> > >> >> #if(true) cool velocity stuff #end
> > >> >> </vel:velocity>
> > >> >>
> > >> >> However, what I really really want is something that lets me use
> > >> >> velocity expressions the way I would use JSTL expressions. The most
> > >> >> important is this:
> > >> >>
> > >> >> <vel:set var="foo" value="${cool.velocity(syntax)}" />
> > >> >>
> > >> >> The inability of JSTL expressions to call arbitrary java methods
> > >> results
> > >> >> in muchhacking and hair pulling. Velocity expressions rock. I want
> > >> >> them :-)
> > >> >>
> > >> >> How hard would it be to make a <vel:set> tag? I looked around the
> > >> APIs
> > >> >> but couldn't find anything helpful.
> > >> >>
> > >> >> Thanks,
> > >> >> Jeff
> > >> >>
> > >> >> ---------------------------------------------------------------------
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> > >> >>
> > >> >>
> > >> >
> > >> >
> > >>
> > >>
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> > >>
> > >>
> > >
> > >
> >
> >
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> >
>
>
> --
> Forio Business Simulations
>
> Will Glass-Husain
> [EMAIL PROTECTED]
> www.forio.com
>
--
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Will Glass-Husain
[EMAIL PROTECTED]
www.forio.com
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Will Glass-Husain
[EMAIL PROTECTED]
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