评估列表是否为空 JSTL

Question

I've been trying to evaluate if this array list is empty or not but none of these have even compiled:

<c:if test="${myObject.featuresList.size == 0 }">                   
<c:if test="${myObject.featuresList.length == 0 }">                 
<c:if test="${myObject.featuresList.size() == 0 }">                 
<c:if test="${myObject.featuresList.length() == 0 }">                   
<c:if test="${myObject.featuresList.empty}">                    
<c:if test="${myObject.featuresList.empty()}">                  
<c:if test="${myObject.featuresList.isEmpty}">  

How can I evaluate if an ArrayList is empty?

Answer 1

empty is an operator :

The empty operator is a prefix operation that can be used to determine whether a value is null or empty.

<c:if test="${empty myObject.featuresList}">

Answer 2

There's also the function tags, a bit more flexible:

<%@ taglib uri="http://java.sun.com/jsp/jstl/functions" prefix="fn" %>
<c:if test="${fn:length(list) > 0}">

And here's the tag documentation.