>On Tue, 28 May 2002, Paul DuBois wrote:
>
>> In an EL expression, does the identifier "null" return to the literal
>> null value, or does it refer to a JSTL variable named "null".
>
>"null" is a keyword in the EL, and it refers to null itself, not a
>variable named "null"
Thanks.
>
>> For example, if I want to explicitly set a variable to null, does this
>> do it?
>>
>> <c:set var="myVar" value="${null}" />
>
>Note that you can't really set a JSP scoped variable to null; you
>can only remove it. <c:set> is specified to remove a variable when its
>'value' attribute is null.
So, for example:
<c:set var="myVar" scope="session" value="${null}" />
would be equivalent to this?
<% session.removeAttribute ("myVar") %>
>
>> I can find reference in the JSTL spec to testing whether the result of
>> an expression is null or empty, but not how to *set* something null
>> explicitly.
>
>The behavior of <c:set> is discussed in section 4.3; its behavior on null
>values is discussed in a section entitled, "Null & Error Handling".
I've read that section, but I wasn't quite clear on how to interpret
it. "null" is never used on constant font there, so I wasn't sure whether
it was a keyword. Thanks for the clarification, that helps.
>
>> I guess a related question is this: You can use the "empty" operator
>> to determine whether a value is null or empty; does "eq null" perform
>> a test that is true *only* for null values?
>
>Right - that's exactly it. empty tests for null, "", and a few other
>things, primarily for the convenience of a page author who doesn't know
>much about data types. You can still test directly against null using the
>'null' keyword.
>
>Shawn
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