Consider following example:

<dl>
  <c:forEach items="${pageContext.response.headerNames}" var="name">
    <c:forEach items="${pageContext.response.getHeaders(name)}" var="value">
      <dt>${name}</dt><dd>${value}</dd>
    </c:forEach>
  </c:forEach>
</dl>

The ${name} is a String. The ${name.class.name} also proves that. The getHeaders(name) call however results in:

org.apache.jasper.el.JspELException: /test.jsp(23,12) '${pageContext.response.getHeaders(name)}' java.lang.NoSuchMethodException: org.apache.catalina.connector.ResponseFacade.getHeaders(java.lang.Object)

Another example which also results in NoSuchMethodException which suggests that an Object is been passed as argument:

<c:set var="name" value="test" />
${pageContext.response.getHeader(name)}

This works all fine on Glassfish v3.