Unable to find a value for "length" in object of class "java.lang.String" using operator "."

Question

Why does this JSTL expression not seem to be able to use the length method of the String class:

    <c:when test="${displayName != null && displayName.length > 0 }">
        <p><c:out value="${displayName}"/></p>
    </c:when>

It produces this exception:

java.lang.RuntimeException: javax.servlet.ServletException: 
javax.servlet.jsp.el.ELException: Unable to find a value for "length" in object 
of class "java.lang.String" using operator "."

I have included the following tag libraries at the top of the JSP:

<%@ page language="java" contentType="text/html; charset=utf-8" pageEncoding="utf-8" isELIgnored="false" %>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="decorator" uri="http://www.opensymphony.com/sitemesh/decorator" %>
<%@ taglib prefix="spring" uri="http://www.springframework.org/tags" %>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<%@ taglib prefix="sec" uri="http://www.springframework.org/security/tags" %>

Answer 1

You can access only getters (getSomething) like this. To find string size, try fn:length(displayName). Naturally, fn namespace should be imported:

<%@ taglib prefix="fn" uri="http://java.sun.com/jsp/jstl/functions" %>

Also, you can replace this all with empty check: ${not empty displayName}

Answer 2

See if this helps.

You'll have to add

<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>