Re: [faces-dev] Outstanding enhancement request for Jakarta EL

[Thomas Andraschko <tandraschko@xxxxxxxxxx>]

Hi Mark,

i think about something like this:
https://github.com/apache/tomcat/blob/master/java/org/apache/el/MethodExpressionImpl.java#L267

try {

     putTempVar("arguments", params);

     Object result = this.getNode().invoke(ctx, this.paramTypes, params);
}

finally {
     removeTempVar("arguments");    
}

Do you know what i mean?

Maybe you have a good idea to implement this easily :) I did a short try it but quite hard to open Tomcat with its Ant build and i dont know the EL internals that good like you.

Best regards,

Thomas

Am Mi., 24. Feb. 2021 um 10:22 Uhr schrieb Mark Thomas <markt@xxxxxxxxxx>:

Hi Thomas,

Can you provide an example of how you would like this to work and the
specific changes you are asking for in the EL API as there are lots of
ways this could be done.

Thanks,

Mark


On 24/02/2021 08:53, Thomas Andraschko wrote:
> Hi Mark,
>
> you may be right that this could be done in JSF only by manual push
> "event" and the obj instance to the ELContext.
>
> But i still think this could be a good change for the EL specs to
> introduce the "arguments" array as there is no way to reference the
> parameters passed to MethodExpression#invoke.
> I like it more to enhance the EL specs instead of changing a
> "implementation detail" in JSF (same as e.g. RequestScoped should be
> implemented in Servlet, not CDI).
> It just makes EL a bit more flexible.
> I think there might be other usescases as well and the implementation is
> quite easy at EL side.
>
> Best regards,
> Thomas
>
>
> Am Di., 23. Feb. 2021 um 15:49 Uhr schrieb Mark Thomas <markt@xxxxxxxxxx
> <mailto:markt@xxxxxxxxxx>>:
>
>     On 22/02/2021 13:40, Thomas Andraschko wrote:
>     > any feedback, Mark? :)
>
>     Hi,
>
>     Sorry I have taken a while to reply.
>
>     I agree with you that there are two solutions as you set out below. More
>     commentary in-line.
>
>     > Am Fr., 5. Feb. 2021 um 12:19 Uhr schrieb Thomas Andraschko
>     > <tandraschko@xxxxxxxxxx <mailto:tandraschko@xxxxxxxxxx>
>     <mailto:tandraschko@xxxxxxxxxx <mailto:tandraschko@xxxxxxxxxx>>>:
>     >
>     >     Hi Mark,
>     >
>     >     just to be clear, this is what JSF always does and i dont
>     think that
>     >     this should be changed, everything should be in EL.
>     >
>     >     MethodExpression me =
>     >     ExpressionFactory#createMethodExpression(context,
>     expressionString,
>     >     new Class[] { AjaxBehaviorEvent.class })
>     >     me.invoke(context, new Object[] {  ajaxBehaviorEventInstance });
>     >
>     >
>     >     I think there are 2 solutions for the EL specs / impl:
>     >
>     >     1) add a syntax to reference a "implicit" param, maybe similar
>     to JS:
>     >         #{bean.method(arguments[0],  someVar)}
>
>     This solution does not require any changes to the EL specification. It
>     does require (relatively simple) changes to the JSF. In summary:
>
>     - define "event" as referring to the appropriate AjaxBehaviorEvent
>
>     - users would then us #{bean.method(event, someVar)}
>
>     - JSF would evaluate this in an ELContext that resolved "event" to the
>       appropriate (creating if necessary) AjaxBehaviorEvent instance
>
>
>     I also looked into several variations of this but for a solution where
>     the user indicates (e.g. via an additional parameter in the method) they
>     want to receive the AjaxBehaviorEvent the approach above is by far the
>     simplest to implement - both for EL and JSF.
>
>
>     >     2) add some auto-lookup-magic into EL, like you mentioned in the
>     >     last mail
>
>     This is more complex that option 1. The search order needs to be well
>     defined. If user specifies #{bean.method(someVar)} then, if both exist,
>     which is used in preference method(event, someVar) or method(someVar)?
>     If there is any requirement to make that preference configurable you are
>     - essentially - back at option 1 and a simpler solution.
>
>     Assuming a preference order can be defined, there needs to be sufficient
>     API exposed to:
>
>     - determine if a method with the additional parameter exists
>     - execute that method with the additional parameter provided by the
>       caller
>
>     How much of this is bundled up into a single API call to EL vs EL being
>     extended with a handful of new generic methods to allow a range of
>     manipulations on MethodExpressions is TBD. The generic approach requires
>     more work in both EL and JSF but provides for greater flexibility.
>
>     >     I >personally< like 1) more as it forces the user to think
>     about the
>     >     method-mapping and is more flexible.
>
>     +1 I think this is the much better solution for this particular problem.
>
>     >     2) is of course also nice but we need a lot of fallbacks. Not sure
>     >     about the performance here, but probably the resolved method is
>     >     cached in the "MethodExpression" instance?
>
>     Maybe. That would be an issue for the EL implementations rather than the
>     API.
>
>
>     So, in summary, I think the best way forward is option one which should
>     be implementable in JSF without any changes to the EL API.
>
>     Kind regards,
>
>     Mark
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