JSTL forEach逆序 [英] JSTL forEach reverse order

问题描述

使用JSTL的 forEach 标记，是否可以按相反的顺序迭代？

Using JSTL's forEach tag, is it possible to iterate in reverse order?

推荐答案

当你使用 forEach 创建一个整数循环时，你可以前进或后退，但它需要一些工作。事实证明你不能这样做，例如：

When you are using forEach to create an integer loop, you can go forward or backward, but it requires some work. It turns out you cannot do this, for example:

<c:forEach var="i" begin="10" end="0" step="-1">
    ....
</c:forEach>

因为规范要求步骤为正。但是你总是可以按顺序循环，然后使用< c：var 将递增的数字转换为递减的数字：

because the spec requires the step is positive. But you can always loop in forward order and then use <c:var to convert the incrementing number into a decrementing number:

<c:forEach var="i" begin="0" end="10" step="1">
   <c:var var="decr" value="${10-i}"/>
    ....
</c:forEach>

但是，当您执行 forEach 时通过任何类型的集合，我不知道有任何方法使对象的顺序相反。至少，不是先将元素排序为相反的顺序，然后然后使用 forEach 。

However, when you are doing a forEach over a Collection of any sort, I am not aware of any way to have the objects in reverse order. At least, not without first sorting the elements into reverse order and then using forEach.

我已成功通过在JSP中执行以下操作，以所需顺序导航 forEach 循环：

I have successfully navigated a forEach loop in a desired order by doing something like the following in a JSP:

<%
List list = (List)session.getAttribute("list");
Comparator comp = ....
Collections.sort(list, comp);
%>


<c:forEach var="bean" items="<%=list%>">
     ...
</c:forEach>

使用合适的比较器，您可以按任何所需顺序循环遍历项目。这很有效。但我不知道如何简单地说，以相反的顺序迭代所提供的集合。

With a suitable Comparator, you can loop over the items in any desired order. This works. But I am not aware of a way to say, very simply, iterate in reverse order the collection provided.

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