如何使用JSTL检查JSP中的请求参数，尤其如此 <c:set> 标签？

Question

I'm trying to parse a request param in my JSP using tags: and

The parameter is namer result, so my variable in jsp is requestScope["result"]

I have two problems exactly: 1) I wanna check two cases: param is null or not, I used the following code

  <c:if test='${not empty requestScope["result"]}'>
    <c:set var = "result" value = '${requestScope["result"] }'/>
  </c:if>
  <c:if test='${empty requestScope["result"]}'>
    <c:set var = "result" value = ' not available'/>
  </c:if>

In order to set the result from request in result variable or "not available" value if it is null

This code always shows not available but when i delete the second test, it shows the result corrctly

Also I tried with '${param.result != null}' test, it gives the same result.

Thank you in advance

Answer 1

我有类似的代码，这种方式适合我：

<c:set var="result" value="${(requestScope['result'] == null || requestScope['result'] eq '') ? 'not available' : ${requestScope['result']}}"/>