了解Struts2中的OGNL表达式 [英] Understanding OGNL expressions in Struts2

问题描述

以下代码使用Struts的<s:a>从1到10显示链接.

The following code displays links using <s:a> of Struts starting from 1 to 10.

<s:set var="currentPage" value="2"/>
<s:set var="begin" value="1"/>
<s:set var="end" value="10"/>

<s:iterator begin="%{begin}" end="%{end}" step="1" var="row" status="loop">
    <s:if test="%{#currentPage eq #row}">    <!--???-->
        <span><s:property value="%{#row}"/></span>
    </s:if>

    <s:else>
        <s:url id="pageURL" action="someAction" escapeAmp="false">
            <s:param name="currentPage" value="%{row}"/>
        </s:url>

        <s:a href="%{pageURL}" name="btnPage" cssClass="paging">
            <s:property value="%{#row}"/>
        </s:a>
    </s:else>
</s:iterator>

当currentPage(为2)与条件表达式test="%{#currentPage eq #row}"匹配时，它仅在<span>内使用<s:property>显示文本，而不显示链接.很好.

When currentPage (which is 2) matches the conditional expression test="%{#currentPage eq #row}", it just displays text using <s:property> inside <span> instead of showing a link. That's fine.

当我使用这些相同的标签但在其相应的动作类中使用适当的属性时，

When I use these same tags but using appropriate properties in its corresponding action class like so,

<s:iterator begin="%{begin}" end="%{end}" step="1" var="row" status="loop">
    <s:if test="%{currentPage eq #row}">   <!--???-->
        <span class="current"><s:property value="%{#row}"/></span>
    </s:if>

    <s:else>
        <s:url id="pageURL" action="someAction" escapeAmp="false">
            <s:param name="currentPage" value="%{row}"/>
        </s:url>

        <s:a href="%{pageURL}" name="btnPage" cssClass="paging">
            <s:property value="%{#row}"/>
        </s:a>
    </s:else>
</s:iterator>

在这种情况下，currentPage(以及所有其他)是操作类中类型为Long的属性.在此，与前一个案例test="%{#currentPage eq #row}"有关的条件测试的评估结果为 false .

In this case, currentPage (and all other) is a property of type Long in the action class. Here, the conditional test regarding the previous case which is test="%{#currentPage eq #row}" is evaluated to false.

它要求在currentPage之前省略#.因此，表达式变为test="%{currentPage eq #row}"(否则，始终的计算结果为false).

It requires the omission of # before currentPage. Hence, the expression becomes test="%{currentPage eq #row}" (otherwise, it always evaluates to false).

我不明白为什么第一种情况要求test="%{#currentPage eq #row}"而第二种情况要求test="%{currentPage eq #row}"?我可能有什么想念的吗?

I don't understand why does the first case require test="%{#currentPage eq #row}" and the second case require test="%{currentPage eq #row}"? Is there anything I might be missing?

推荐答案

当您<s:set>值时，它不在 值堆栈中，而是 in 中的值堆栈上下文".

When you <s:set> a value it's not on the value stack, but instead in the "value stack context".

使用裸currentPage引用仅搜索实际的堆栈，而不是上下文.

Using the bare currentPage reference only searches the actual stack, not the context.

使用#currentPage不会检查堆栈本身，而是引用堆栈 context .

Using #currentPage doesn't check the stack itself, but instead references the stack context.

也请参见以下其他答案:

See these other answers as well:

1. #{} $ {}和％{}有什么区别?
2. Struts 2％"签署和#"登录OGNL

1. what's the difference between #{} ${} and %{}?
2. Struts 2 "%" sign and '#" sign in OGNL

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