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From Ryan Lubke <Ryan.Lu...@Sun.COM>
Subject Re: incorporating EL support
Date Thu, 12 Sep 2002 16:58:30 GMT
On Thu, 2002-09-12 at 12:45, Craig Longman wrote:
> On Thu, 2002-09-12 at 12:14, peter lin wrote:
> > 
> > 
> > You should know that JSP2.0 includes EL built in.  the early access
> > implementation of JSP2.0 uses JSTL's el.
> 
> oh, ok.  well, that's good news.  i guess that splits my question into a
> couple pieces:
> 
> 1) jsp2.0 including EL, does that mean that the way one evaluates an EL
> parameter will change, or that explicit evaluation will no longer be
> necessary

If using JSP 2.0 EL machinery, then you will not have to perform
explicit evaluation in the tag library.  The container will take care
of this at runtime.

> 2) is there a way of determining ( in a tag ) to determine what the JSP
> level container we're executing in.  then the tag (during a phase-in
> period at least) could determine whether to explicitly evaluate it or
> not.
I think one approach is that if you don't want the container to evaluate
EL expressions, you can package the app using a Servlet 2.3 deployment
descriptor.  JSP 2.0 containers will not perform EL evaluation in that
case.  I also believe that if you use JSTL EL, and you want JSTL to
perform the EL evaluation you could also set a page property isELEnabled
to false and the container will not evaluate EL expressions.

I think there is a third option using a 2.4 deployment descriptor and
using a jsp-property-group to disable EL across a set of pages
identified by a URL pattern.

If you let the JSP 2.0 container evaluate the EL in a JSTL tag, then it
should be passed to JSTL as the evaluated value and you should have no
problems.

> 
> and a third question i suppose:
> 3) is explicitly evaluating EL really as simple as calling
> ExpressionEvaluatorManager.evaluate() (as below), or is there some other
> prep/setup work i haven't noticed yet in the bowels of the current jstl
> package?

Will defer to someone more familiar with the EL machinery.

> 
> > You may want to look at the draft spec to familiarize yourself with the
> > changes that will occur when JSP2.0 is released. 
> 
> i'll try and track it down, thanks.
> 
> > peter lin
> > 
> > Craig Longman wrote:
> > > 
> > > hi there,
> > > 
> > > i'm just starting out with jsp/taglibs, and have decided to focus on
> > > using the jstl as the basis for my efforts.  it seems to provide exactly
> > > what i needed, some basic, compatible tags to get started.
> > > 
> > > it is clear, however, that i'm going to have to write my own tags to get
> > > any serious work done.
> > > 
> > > my question is this,  i figure that if i'm going to standardize on the
> > > jstl, then it only makes sense to standardize on the EL stuff also, i
> > > prefer its style to the scriplet thingies, and its less typing.  but,
> > > i'm wondering what the preferred/recommended method is for doing this.
> > > 
> > > i see in the src dist for the reference jstl that there are a couple of
> > > classes that look promising to use.  one is an interface
> > > (ExpressionEvaluator) and then an implementing class
> > > (ExpressionEvaluatorManager).  using it appears to be as simple as this
> > > (from tag/el/core/ForEachTag.java):
> > > 
> > >   if( begin_ != null )
> > >   {
> > >     Object r = ExpressionEvaluatorManager.evaluate(
> > >                   "begin", begin_, Integer.class, this, pageContext );
> > >     if (r == null)
> > >     {
> > >       throw new NullAttributeException("forEach", "begin");
> > >     }
> > >     begin = ((Integer) r).intValue();
> > >     validateBegin();
> > >   }
> > > 
> > > it is acceptable to utilize this class in this manner for custom tags?
> > > or is there a better/standard way.  i have been unable to find any docs
> > > that talk about using the standard EL in your own tags, but if anyone
> > > has any pointers, i would greatly appreciate it.
> > > 
> > > thanks,
> > > 
> > > --
> > > 
> > >     CraigL->Thx();
> > >     Be Developer ID: 5852
> > > 
> > >   ------------------------------------------------------------------------
> > >                        Name: signature.asc
> > >    signature.asc       Type: application/pgp-signature
> > >                 Description: This is a digitally signed message part
> > 
> > --
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> > For additional commands, e-mail: <mailto:taglibs-user-help@jakarta.apache.org>
> > 
> -- 
> 
>     CraigL->Thx();
>     Be Developer ID: 5852
> 



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