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From "Asleson, Ryan" <asle...@BIWORLDWIDE.com>
Subject RE: Dynamic Expressions for Struts-EL and JSTL
Date Thu, 02 Sep 2004 15:32:40 GMT

We must be close.  I tried this:


<c:out value="${formBean[layoutObject.property]}"/>
(Assume that layoutObject.property evaluates to a String of
userInfo.firstName)


And the container threw this exception:



[ServletException in:/jsp/registration/registerDisplay.jsp] An error
occurred while evaluating custom action attribute "value" with value
"${formBean[layoutObject.property]}": Unable to find a value for
"userInfo.firstName" in object of class "app.MyFormBean" using operator "[]"
(null)' javax.servlet.jsp.JspException: An error occurred while evaluating
custom action attribute "value" with value
"${formBean[layoutObject.property]}": Unable to find a value for
"userInfo.firstName" in object of class "app.MyFormBean" using operator "[]"
(null) at
org.apache.taglibs.standard.lang.jstl.Evaluator.evaluate(Evaluator.java:146)
at



Like I said before, I want c:out to output the resulting String of
formBean.getUserInfo.getFirstName, but it won't do it.  Any more ideas??  I
have to believe this can be done somehow using these tags.






-----Original Message-----
From: Helios Alonso [mailto:halonso@atg.com.uy]
Sent: Thursday, September 02, 2004 9:48 AM
To: Tag Libraries Users List
Subject: Re: Dynamic Expressions for Struts-EL and JSTL



So, you could change this:

>String expr = "formBean." +
>((app.LayoutObject)pageContext.getAttribute("layoutObject")).getProperty();

to this:

formBean[pageContext.layoutObject.property]

(If I understood you have a layoutObject with a property saying which 
property read from formBean).

At 08:37 02/09/2004 -0500, you wrote:

>Hello,
>
>I'm using the Struts-EL and JSTL custom tag implementations in my Web app.
>
>I want to use the c:out tag to output dynamic data.  The tricky part is I
>want to dynamically build the EL expression at runtime by building up a
>String that should be evaluated.  I don't want to output the String, I want
>the String to be evaluated by the expression engine and then that written
>out.  An example follows below.
>
>
>
><%
>//Assume that after this line runs, expr has a value of
>formBean.property.value
>//This is the expression I want evaluated
>String expr = "formBean." +
>((app.LayoutObject)pageContext.getAttribute("layoutObject")).getProperty();
>
>pageContext.setAttribute("expr", expr);
>%>
>
><c:out value="Expression Value is: ${expr}" />
>
>
>
>The c:out tag above renders the text Expression Value is:
>formBean.property.value  .
>
>This isn't what I want -- I want it to evaluate the formBean.property.value
>down to an expression, and then spit out the value of that expression
>(basically, formBean.getProperty().getValue() ).
>
>Interestingly, if I "hard code" the expression, it works:
>
><c:out value="${formBean.property.value}"/>
>
>The only problem is I need to dynamically change this expression at
runtime.
>
>Can this be done?  If so, how?  I'm hoping so otherwise I'll have a
mountain
>of new code to write.  Also, is there a more elegant way to do what I show
>in the example above, like using tags instead of scriptlets?  I don't care
>if I use Struts-EL tags, JSTL tags, or both.
>
>Thank you very much!!
>
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