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Assigning form input value to java variable in jsp

I have a scenario in which i am rendering a jsp page .One of my value is in my model Form entity.I am assigning it in one of my form input like below :
<s:hidden name="myModelName.myUserName"/>
I am trying to assign it to my java variable inside my jsp.I tried accessing the model directly like this
<%= String myName = myModelName.myUserName %>
But i get error message "myModelName cannot be resolved.I have then tried accessing from the hidden field.But i dont know how to use it.Anyway i need the value in java variable inside jsp for some reason.Anyone help me out how to do it

You can do something like this:
assign your model property value to variable userName
<c:set var="userName" scope="session" value="${myModelName.myUserName}"/>
and then you can output it using this tag:
<c:out value = "${userName}"/>
You can read more about JSTL tags here: Using JSTL tags
Hope this helps. Ask if you need anything else.

Java JSP Using Include with Variable Parameters

I'm trying to pass a parameter to the jsp file that I am including in my main jsp. From what I've seen online the way to do this using c:set
approot/index.jsp
<c:set var="Arg01" value="Argument01"/>
<jsp:include page="include/other.jsp">
<jsp:param name="myArg01" value="${Arg01}"/>
<jsp:param name="myArg02" value="Argument02"/>
</jsp:include>
Although when I try to use the variables in the included jsp page only the one argument seems to be coming through (the second one which is not using c:set)
approot/include/other.jsp
<!-- this doesn't work -->
<p>${param.myArg01}</p>
<!-- this does -->
<p>${param.myArg02}</p>
Nothing crashes but I can see that myArg01 is blank

This way of getting around it is probably awful but it's the only way I could find to get around the issue.
I used a different kind of include in my main JSP
public static String myArg01 = "Argument01";
public static String myArg02 = "Argument02";
<%# include file="include/other.jsp" %>
Then I could reference the variables directly inside the included JSP file
<p><%= myArg01 %></p>
<p><%= myArg02 %></p>

How to Pass tag attribute value to Java Bean in JSP

Im trying to pass the string fro jsp page to .tag via attribute but the value isnot passing to the java bean in that tag file.
Following is the code in JSP File
<t:detailPane lang="English" ></t:detailPane>
Tag File :
<%#attribute name="lang" required="true"%>
<jsp:useBean id="language" scope="page" class="com.AAA.Test.Language" ></jsp:useBean>
<%=language.getWord("DepartureCaption", "${lang}") %>
If i write "English" or "Urdu" or "French" instead of ${lang} it works fine but doesnt work when i use the attribute in the tag file to pass value to java bean.

Following is the java markup i have found to get attribute
jspContext.getAttribute("lang").toString();
It helped in my code as :
<%String lan = jspContext.getAttribute("lang").toString(); %>
<%=language.getWord("DepartureCaption", lan) %>

PHP's variable variables analog in JSTL

In PHP we can do the following with the help of Variable variables in PHP:
$privateVar = 'Hello!';
$publicVar = 'privateVar';
echo $$publicVar; // Hello!
Suppose we have the following chunk of Java code:
request.setAttribute("privateVar", "Hello!");
request.setAttribute("publicVar", "privateVar");
I've tried the following but an error occurs.
${${publicVar}}
Does anyone know how we can get value of privateVar via using only publicVar in JSP (JSTL)?
UPDATE 1:
I have a custom tag which allows to print a message if an object foo doesn't have a field bar.
I know I must catch exceptions in the case but I don't want to handle ones in JSP. I want to do it only in CustomTag file.
<%-- JSP file --%>
<ctf:tagName varName="foo.bar" />
<%-- CustomTag file --%>
<%# attribute name="varName" required="true" rtexprvalue="true"%>
<c:catch var="exception">
<c:set var="valX" value="${${varName}}" scope="page"/>
</c:catch>
<c:if test="${exception != null}">Can't find getter for the VAR in the OBJ.</c:if>
UPDATE 2:
JB Nizet gave me the answer and the following works well! :)
<c:set var="privateVar" value="Hello!" />
<c:set var="publicVar" value="privateVar" />
${pageScope[pageScope.publicVar]}

I don't think you can directly do this in the same way that you can in PHP. Instead you could change the attribute to use the value of the privateVar instead of the name, like this:
String privateVar = "Hello!";
request.setAttribute("privateVar", privateVar);
request.setAttribute("publicVar", privateVar);
This gives you access to the value under both names, which I think is the closest you'd get. No need to even put the attribute privateVar in the request if you are ultimately going to use publicVar on the JSP.
Ultimately you may want to rethink the design here as it doesn't really work in Java.

The basics:
That's not JSTL but Expression Language. And you should only use a single ${} evaluator. The code would be:
${publicVar}
More info:
StackOverflow Expression Language wiki
To your problem:
Expression Language doesn't allow that. You cannot have private attributes in any scope (page, request, session, application), so you can at most set the attribute twice with different names but the same value. But as you may note, this is useless.

JSP.13.8 Example Simple Tag Handler Scenario doesn't work?

This test was prompted by reading a question on the Sun java forums and thought I would try it out.
The JSP2.0 specification section JSP.13.8 contains an "Example Simple Tag Handler Scenario". I copy and pasted the code fragments and attempted to run it.
Environment:
Apache Tomcat version 5.5.26 and 6.0.14 (tested on both)
Java: 1.5
Code I am testing with:
Jsp page:
<%# taglib prefix="my" tagdir="/WEB-INF/tags" %>
<my:simpletag x="10">
<jsp:attribute name="y">20</jsp:attribute>
<jsp:attribute name="nonfragment">
Nonfragment Template Text
</jsp:attribute>
<jsp:attribute name="frag">
Fragment Template Text ${var1}
</jsp:attribute>
<jsp:body>
Body of tag that defines an AT_BEGIN
scripting variable ${var1}.
</jsp:body>
</my:simpletag>
And the tag file:
<%-- /WEB-INF/tags/simpleTag.tag --%>
<%# attribute name="x" %>
<%# attribute name="y" %>
<%# attribute name="nonfragment" %>
<%# attribute name="frag" fragment="true" %>
<%# variable name-given="var1" scope="AT_BEGIN" %>
<%# taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
Some template text.
<c:set var="var1" value="${x+y}"/>
<jsp:invoke fragment="frag" varReader="var1"/>
Invoke the body:
<jsp:doBody/>
This code is directly copied from the PDF copy of the JSP2.0 specification.
It is also available as part of the JSP-API here
Minor change made - I changed the name of the tagfile from simpletag.tag to simpleTag.tag to match the invocation of it in the JSP.
I also tried copying from the PDF of the spec (adjusting quotes as necessary) - same result.
When I execute the page I end up with a standard 500 error
Root cause:
java.lang.ClassCastException: java.io.StringReader
org.apache.jsp.tagVariableTest_jsp._jspService(tagVariableTest_jsp.java:62)
Line62 of the generated JSP turns out to be:
var1 = (java.lang.String) _jspx_page_context.findAttribute("var1");
Ok, I can understand ClassCastException - it thinks that var1 should be a String, and the actual attribute is a StringReader. But why is it a StringReader? Where did the variable get created? And why is it attempting to do this assignment at all?
Can someone please point me in the right direction?
What is wrong with the code/setup?
Is this a known issue? I googled for it but couldn't seem to find anything.
Thanks,
evnafets
Editing with resolution:
The ClassCastException was being caused by the line in the tag:
<jsp:invoke fragment="frag" varReader="var1"/>
As mentioned here the varReader attribute specifies the attribute to store the evaluation result as a StringReader. The exception was caused by Tomcat generated code trying to retrieve the value of "var1" and cast it to a String. As a String is not a StringReader so, it raised an exception at that point.
I'm not sure if the coding error is they should have used the "var" instead of the "varReader" attribute, or they shouldn't have used either and just evaluated it as is.
Removing that attribute completely prints out the fragment, and then the body both with the value of "var1":
Fragment Template Text 30.
Invoke the body: Body of tag that defines an AT_BEGIN scripting variable 30
Making the attribute var="var1" executes the fragment, and stores the result to var1. The body is then evaluated with this new value of var1 resulting in:
Invoke the body: Body of tag that defines an AT_BEGIN scripting variable Fragment Template Text 30
Personally I think the first case makes more sense, but this code is presented as an example of the innerworkings, not best practice.
I still would have expected the example to compile/run in any case. I was fairly surprised when it didn't.

From the syntax reference you can see that either var or varReader is
The name of a scoped attribute to store the result of the fragment invocation in
So I am afraid the sample code contains an error. If you need to write the result of jsp:invoke directly to the page you do not need to assign it to a var.
Can you try leaving out the "varReader" attribute?