expression language - header value is null

Question

In .jsp pages by using Expression Language, i am wanting to retrieve all header names along with their values.

<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<table>
    <tr>
        <th>Name</th>
        <th>Value</th>
    </tr>
    <c:forEach items="${pageContext.request.headerNames}" var="item">
    <tr>
        <td>${item}</td>
        <td>${header["${item}"]}</td>
    </tr>
    </c:forEach>
</table>

header is as far as i know a map

The quotation marks are required for specifying a property in a JavaBean or a key in a map

But <td>${header["${item}"]}</td> return null, even though <td>${item}</td> return the header name.

This is not an duplicate of that. – Cristian Matthias Ambæk Aug 08 '17 at 12:59 — Cristian Matthias Ambæk, Aug 08 '17 at 12:59

score 2 · Accepted Answer · answered Aug 08 '17 at 11:37

2

<td>${header["${item}"]}</td>

should be

<td>${header[item]}</td>

Alternatively you could use the implicit header object in jstl

<c:forEach items = "header" var = "h">

Header Name ${h.key}
Header Value ${h.value}

</c:forEach>

answered Aug 08 '17 at 11:37

ramp

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Without quotation mark in my example = Failed to parse the expression [${header[${item}]}] but it worked like a charm to iterate over the header object and get the key and value. – Cristian Matthias Ambæk Aug 08 '17 at 12:22
Please look carefully :), the item does not have a '$' or a '{' surrounding it. Its just plain [item] – ramp Aug 08 '17 at 12:38
I see now, been looking at this for too long xD I tried it out but i get an javax.servlet.jsp.el.ImplicitObjectELResolver$ScopeMap$ScopeEntry cannot be cast to java.lang.String --- ${header[item]} – Cristian Matthias Ambæk Aug 08 '17 at 12:47
Oh wow, its a Map.Entry. Maybe you should try item.key in place of item. Sorry I dont have a working environment to try it out – ramp Aug 08 '17 at 12:50
Than it works :) – Cristian Matthias Ambæk Aug 08 '17 at 13:02

expression language - header value is null

1 Answers1