Java 评估列表是否为空 JSTL

Evaluate if list is empty JSTL

提问by OscarRyz

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

我一直在尝试评估这个数组列表是否为空，但这些都没有编译：

<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?

如何评估 ArrayList 是否为空？

采纳答案by bobince

emptyis an operator:

empty是一个运算符：

The emptyoperator is a prefixoperation that can be used to determine whether a value is null or empty.

所述empty操作者是一个前缀，可以被用来确定一个值是否为空值或空白操作。

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

回答by Steve B.

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

还有功能标签，更灵活一点：

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

And here'sthe tag documentation.

而这里的标签文档。