How to pass java variables from scriptlets to c:when expression in jstl?

Question

what is a proper way to use variables from scriptlets in jstl? I don't know what is wrong in my code:

<%
boolean a = true;
boolean b = false;
%>

<c:choose>
    <c:when test="${a}">
        <c:set var="x" value="It's true"/>
    </c:when>
    <c:when test="${b}">
        <c:set var="x" value="It's false"/>
    </c:when>

</c:choose>

It looks like it doesn't go into the whole block.

score 14 · Accepted Answer · edited May 23 '17 at 12:01

14

Variables in scriptlets cannot be seen in JSTL because Expression Language, the stuff between ${} used in JSTL, will look for attributes in page, request, session or application. You have to at least store the variable from scriptlet in one of these scopes, then use it.

This is an example:

<%
    boolean a = true;
    request.setAttribute("a", a);
%>

<c:if test="${a}">
    <c:out value="a was found and it's true." />
</c:if>

More info:

As a recommendation, stop using scriptlets. Move the business logic in your JSP to controller and the view logic into EL, JSTL and other tags like <display>. More info: How to avoid Java code in JSP files?

edited May 23 '17 at 12:01

Community

1
1

answered Sep 17 '14 at 14:58

Luiggi Mendoza

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What is the difference between using `request.setAttribute` and `pageCotnext.setAttribute` ? I want to my temp variables to be as short lived as possible, and only available during the rendering of that single jsp file. – Tamas Hegedus Apr 29 '16 at 19:36
@TamasHegedus this is related to the scope of the variable. Please see [How to pass parameter to jsp:include via c:set? What are the scopes of the variables in JSP?](http://stackoverflow.com/a/16619110/1065197) – Luiggi Mendoza Apr 29 '16 at 22:54

score 0 · Answer 2 · answered Sep 18 '14 at 08:59

The default scope of JSP is page. if you want to use the variable of scriplet to JSTL use following code.

<%
    boolean a = true;
    boolean b = false;
    pageContext.setAttribute("a", a);
    pageContext.setAttribute("b", b);
%>

Then it will be usable in JSTL.

How to pass java variables from scriptlets to c:when expression in jstl?

2 Answers2

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