Java – JSTL: check whether the string is empty

See the English answer > evaluate empty or null JSTL C tags8

This is hard coding I'm trying to replace with JSTL This code works correctly:

<% if (request.getAttribute("error") != null) { %>
    <div class="alert alert-danger">
        <strong>Oh snap,something's wrong,maybe the following error Could help you out?<br /></strong>
        <%= request.getAttribute("error")%>
    </div>
<% } %>

This is how I replace it with JSTL When selected, the error attribute is not empty, but it is empty

<c:if test="${not empty sessionScope.error}">
    <div class="alert alert-danger">
        <strong>Oh snap,maybe the following error Could help you out?<br /></strong>
        <c:out value="${sessionScope.error}" />
    </div>
</c:if>

Solution

Add the JSTL library and declare the core taglib:

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

JSTL is equivalent to

<% if (request.getAttribute("error") != null) { %>

yes

<c:if test="${not empty error}">