EL表达式错误

Question

我正在尝试一起使用fn:length和c:when

<c:when test="${fn:trim(${properties.num2display})== null}">
    <c:set var="counter" value="3"/>
    condition 1 
</c:when>

给我错误：

contains invalid expression(s): javax.el.ELException: Error Parsing:
    ${fn:trim(${properties.num2display})== null}

在fn:trim内写表达式的正确方法是什么？

Answer 1

试试这个：

<c:when test="${not empty fn:trim(properties.num2display)}">
    <c:set var="counter" value="3"/>
    condition 1 
</c:when>