Hi,
I don't know the exact explanation and reasons why it behaves that
way, but looking at the code I can say it's by design :)
<s:param/> tag doesn't play alone, you must use it in context of other
tag so it is natural that its "value" attribute should be evaluated as
an expression - you can read this as: evaluate expression of "value"
attribute and assign its result to property of "name" attribute. You
can call it a "named expression" :)
Other tags' "value" attribute has the same meaning as value attribute
of normal html tags (ie. <input/>) - it represent that tag's value.
You can tell Struts to evaluate "value"'s value by defining an
expression with %{} or ${} - it forces Struts to treat "value"'s value
as OGNL expression - it has nothing to do with EL expressions. In that
context you can treat <s:param/> as manifestation of %{}/${} but
result of evaluating "value" attribute will be assigned to property
named by "name" attribute. ${}/%{} is an anonymous though :)
I hope you will understand, if not ask :)
Regards
--
Lukasz
2016-03-04 18:30 GMT+01:00 Steven Willis <swil...@cargurus.com>:
> I was having some issues with how freemarker/struts handles the 'value'
> attribute on the 'param' tag. I figured it out and saw that struts will try
> to evaluate any string passed in to 'value'. Freemarker had been evaluating
> my expressions, sending in the resulting string to struts, and struts was
> evaluating it again.
>
> After figuring that out, I assumed that other tags, like 'hidden' would
> behave the same way with their 'value' attribute, but that doesn't appear to
> be the case. It seems like I need to do the following for the 'param' tag:
>
> <@s.param name="foo" value="someProperty"/>
>
> But with the hidden tag (or I'm assuming any form-based tag) I have to do:
>
> <@s.hidden name="foo" value=someProperty/>
>
> or:
>
> <@s.hidden name="foo" value="${someProperty}"/>
>
> Is this the expected behavior? And if so, why the different handling of the
> value attribute between the different tags? This page:
> https://struts.apache.org/docs/tag-syntax.html#TagSyntax-valueisanObject%21
> seems to indicate that all value attributes are evaluated and even gives the
> example of a textfield. But the behavior I'm seeing with hidden is that if
> you used value="someProperty", you'd get the literal string value:
> "someProperty" in the html, not the result of evaluating "someProperty"
> against the value stack.
>
> Also, the table of parameters for all of the following tags:
>
> https://struts.apache.org/docs/hidden.html
> https://struts.apache.org/docs/textarea.html
> https://struts.apache.org/docs/textfield.html
> https://struts.apache.org/docs/param.html
>
> Indicate that 'value' is a String field, even on the param page where the
> 'Description' section indicates exactly the opposite.
>
> Is there a place I could see definitively which attributes are evaluated
> against the value stack and which are taken as-is? Or am I just
> missing/not-understanding something (very likely)?
>
> -Steven Willis
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