这个条件有什么作用呢？
<c:if test="${not empty userList)}">
<table cellpadding="5">
<tr class="even">
<th>Name</th>
<th>Gender</th>
<th>Country</th>
<th>About You</th>
</tr>
<c:forEach items="${userList}" var="user" varStatus="status">
<tr class="<c:if test="${status.count % 2 == 0}">even</c:if>">
<td>${user.name}</td>
<td>${user.gender}</td>
<td>${user.country}</td>
<td>${user.aboutYou}</td>
</tr>
</c:forEach>
</table>
</c:if>
当我删除
<c:if test="${not empty userList)}">
<table cellpadding="5">
<tr class="even">
<th>Name</th>
<th>Gender</th>
<th>Country</th>
<th>About You</th>
</tr>
<c:forEach items="${userList}" var="user" varStatus="status">
<tr class="<c:if test="${status.count % 2 == 0}">even</c:if>">
<td>${user.name}</td>
<td>${user.gender}</td>
<td>${user.country}</td>
<td>${user.aboutYou}</td>
</tr>
</c:forEach>
</table>
</c:if>
When i remove <c:if test="${not empty userList)}"></c:if> it throws me error.
What does this condition check? My DB tables has users list, but yet this entire code is not displayed in my HTML itself.
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评论（3）
该行相当于
that line is equivalent to
它检查列表是否包含数据，如果包含则可以使用 foreach。如果您在空列表或 null 列表上使用 foreach，它将引发异常。
It checks if the list contains data if so the foreach can be used. If you use a foreach on an empty or null list it will throw an exception.
这让我感到惊讶。我希望它是相反。我希望当您删除该行时错误就会消失。也就是说，它在语法上是无效的。以下内容在语法上是有效的：
在以后的问题中，请同时发布确切的错误消息和跟踪。他们即讲述了问题的原因。您知道，一旦理解了某个问题的原因，那么解决方案就不言自明了。
That surprises me. I would expect it to be the other way round. I would expect that the error disappears when you remove that line. It's namely syntactically invalid. The following is syntactically valid:
In future questions, please post the exact error message and trace as well. They namely tell something about the cause of the problem. You know, once the cause of a certain problem is understood, then the solution would speak for itself.