Re: JSTL <c:if ....

From:

Lew <lew@nospam.lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Fri, 25 May 2007 10:03:58 -0400

Message-ID:

<PLedndF2drBSccvbnZ2dnUVZ_tCtnZ2d@comcast.com>

Tim Slattery wrote:

Tim Slattery <Slattery_T@bls.gov> wrote:

I have an object (ContactModel). One of its methods is named
"isEmailAddressNull" and returns a boolean. I'm trying to query that
field from a <c:if ... tag in a JSP page. I get no error messages, but
I get the wrong values. The relevant part of the page looks like this:

<c:if test="${!(ContactBean.emailAddressNull)}">
<a id="UpdateEmail" href="/CESLite/Email.do"
class="menu" title="Update Email Address">Update Email
Address</a> | 
</c:if>

Coded this way, the link *always* appears, regardless of the value
returned by isEmailAddressNull. If I change it to:

<c:if test="${ContactBean.eMailAddressNull == false}">

then the link *never* appears, regardless of the value returned.

Addendum: I guess this has to do with negating the value I'm
retrieving. When I use a <c:choose> group like this:

<c:choose>
  <c:when test="${ContactBean.emailAddressNull}">
  </c:when>
  <c:otherwise>
      stuff I want to appear when email address is non-null
  </c:otherwise>
</c:choose>

It works fine. I don't get it.

I don't either, assuming the boolean test worked the same both times and that
the parentheses didn't matter. Have you tested with equivalent constants?

<c:if test="${! true }" >

There's another syntax that, assuming there is an attribute 'emailAddress' in
ContactBean, avoids duplicating information in the bean (maintaining both the
address and the flag copying the state) and eliminates the redundant boolean
is...() method:

<c:if test="${! empty ContactBean.emailAddress}" >

which has the virtue of handling the value being null or empty.

--
Lew