Here are the language and developer guides:
http://www.opensymphony.com/ognl/
I'm pretty sure that neither %{} nor ${} are actually part of OGNL. %{} is a
marker for struts2 that the content should be evaluated as OGNL-Statement and
not as String while ${} is the marker for freemarker, which is used in Struts2
to generate html from tags, that the content should be evaluated with a
customized data model which wraps the value stack.
The ValueStack isn't part of OGNL either. It's just a class with the special
behavior regarding to OGNL. Normally OGNL walks the object path like this:
>>>>>>>>>>>>>>>>>>>>>
Map m = new Map();
m.put( "model",new DomainModel() ); //DomainModel has the Property id;
<<<<<<<<<<<<<<<<<<<<<
OGNL can now retrieve the ID with "m['model'].id"
The Value Stack now hides the fact that it's not the value stack that has a
property but object that was given to it.
>>>>>>>>>>>>>>>>>>>>>>
ValueStack v = new ValueStack();
v.push( new DomainModel() );
<<<<<<<<<<<<<<<<<<<<<<
this is why OGNL can now ask "v.id" (and not "v.top.id") as if the ID was a
property of the stack.
Because the Actionclass-Instance is added to the ValueStack automatically and
every expression is evaluated against the value stack you can write "id" and
retrieve the getId()-property of the action.
The action is the root of the context map wich uses OGNL as a starting point
therefore you don't need the '#'-before the name of the variable.
Normally when looking for a property on the value stack the first occurence of
it (starting at the top of the stack) is returned. But some tags (eg. property)
only evaluate 'top' which is the last element that was pushed on the Value
Stack (which is the action instance itself at the start of the evaluation of
you JSP/Freemarker/Velocity page).
/Stephan
-------- Original-Nachricht --------
> Datum: Fri, 22 Aug 2008 17:32:34 +0530
> Von: "Muralidhar Y" <[EMAIL PROTECTED]>
> An: "\'Struts Users Mailing List\'" <user@struts.apache.org>
> Betreff: OGNL
> Hi friends,
>
> How to understand the OGNL. I am working with it, most
> of
> the time I guess the things but I want to know how exactly the OGNL works.
> What is value stack? What is root and exactly how to write OGNL? Apart of
> the doc that is there on struts site, is there any good tutorial for OGNL
> so
> that I don't need to guess when writing OGNL when writing jsp pages using
> struts? I am really confused? Sometimes we use "%{}" notation, sometimes
> we
> use "${}" notation? Which is OGNL? I am really confused? Kindly help me in
> this.
>
>
>
> Warm regards,
>
> Muralidhar Y
>
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