JSTL conditional check | 易学教程

问题

On my current page I am using JSTL to check if data is available for my form. Problem I am facing is "if there is no data I am not seeing the text fields either". I can solve it using and tags but that would entail lot of if else if else kind of code all through the page. Can anyone suggest me a better cleaner solution to this problem?

<c:if test="${salesData!=null}">
  <c:if test="${fn:length(salesBundle.salesArea) > 0}">
  <input type="text" id="sales_area" class="salesManagerStyle">
  </c:if>
</c:if>

回答1:

You can have multiple conditions in a test.

<c:if test="${salesData != null && fn:length(salesBundle.salesArea) > 0}">
    <input type="text" id="sales_area" class="salesManagerStyle">
</c:if>

But you can also use the empty keyword to do both a nullcheck and lengthcheck.

<c:if test="${not empty salesData.salesArea}">
    <input type="text" id="sales_area" class="salesManagerStyle">
</c:if>

That's the best what you can get, now. If you need to reuse the same condition elsewhere in the page, then you could also save it by <c:set>.

<c:set var="hasSalesData" value="${not empty salesData.salesArea}" />
...
<c:if test="${hasSalesData}">
    <input type="text" id="sales_area" class="salesManagerStyle">
</c:if>
...
<c:if test="${hasSalesData}">
    Foo
</c:if>

回答2:

I try to put as little logic as possible in my web pages,

"The interface tier is relatively free of application processing; windows or web pages forward task request to middle tier" Graig Larman, Applying UML and Patterns third Edition page 575 - Information Systems: The classic Three-tier architecture.

Also do the control/validation at the client level before persisting the data...but I guess if it is legacy and web pages are the only things you can touch ...this makes sens

来源：https://stackoverflow.com/questions/6219730/jstl-conditional-check

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