Glenn,
You're right: thanks for the correction. The scriplet should read
<%
String a = "foo";
String b = new String(a);
pageContext.setAttribute("a", a);
pageContext.setAttribute("b", b);
%>
The point remains: the JSTL expression language's '==' operator leads to
a call to equals() when Strings are being compared. Marba's originally
problem wasn't related to the '==' operator but to the structure of the
<sql:query> tag's Result objects themselves. (Marba was using an old
Result implementation.)
Thanks again.
--
Shawn Bayern
Author, "JSP Standard Tag Library" http://www.jstlbook.com
(coming this summer from Manning Publications)
On 10 Apr 2002, Glenn R. Kronschnabl wrote:
> Shawn,
>
> Just to clarify - your code snippet is very misleading. The reason
> <c:if test="${a == b}"> evaluates to true is because null == null, not
> because "a == b" where a = "foo". a & b are not in any scope so in the
> EL, a & b are null - in fact it doesn't matter what you set a or b to.
>
> Changing your example a little:
>
> <%
> String s1 = "string1";
> String s2 = "string2";
> %>
>
> s1 = <c:out value="${s1}"/>, s2 = <c:out value="${s2}"/>,
>
> <c:if test="${s1 == s2}">s1 == s2</c:if>
>
> Surprisingly, you'll see "s1 == s2" on the output. Of course you'll
> also see from the line above that "s1 = , s2 = ", that is, you're
> referencing bogus variables.
>
> Anyways- thought I would clarify for other users out there.
> This does point out a danger in the test= stuff, since you reference
> bogus variables without error, you may not be actually testing what you
> think you're testing.
>
> Let me know if I'm incorrect.
>
> Thanks,
> Glenn
>
>
> On Tue, 2002-04-09 at 09:57, Shawn Bayern wrote:
> > Are you sure the strings are really identical? For instance, just to be
> > sure you're using two different Strings with the same value, you can
> > experiment via the String copy constructor. Doing this demonstrates that
> > JSTL's '==' operator does work correctly:
> >
> > <%@ taglib prefix="c" uri="http://java.sun.com/jstl/ea/core"; %>
> >
> > <%
> > String a = "foo";
> > String b = new String(a);
> > %>
> >
> > <c:if test="${a == b}">
> > a indeed equals b
> > </c:if>
> >
> > Make sure that the two strings in your database don't have different
> > amounts of whitespace, are indeed of the same case (uppercase, lowecase,
> > etc.), and so on. I often find it useful to print out values with a
> > marker (e.g., the ' character) on both sides to make sure I'm not missing
> > any whitespace.
> >
> > --
> > Shawn Bayern
> > Author, "JSP Standard Tag Library" http://www.jstlbook.com
> > (coming this summer from Manning Publications)
> >
> > On Tue, 9 Apr 2002, marba wrote:
> >
> > > I'm try to compare two string fields in a MySql table row
> > > here's my code that evaluate false even if the strings are identical:
> > >
> > > <sql:query var="filiali" dataSource="${ds}">
> > > SELECT * FROM FILIALI_EXT_LOG LEFT JOIN FILIALI_EXT USING (ID)
> > > WHERE FILIALI_EXT_LOG.LASTMODI > <c:out
> > > value="${user.lastTimeStamp}"/>
> > > </sql:query>
> > >
> > > <c:forEach var="row" items="${filiali.rows}">
> > > <c:set var="campi" value="51"/>
> > > <c:forEach var="i" begin="0" end="${campi}">
> > >
> > > <c:if test="${row.columns[i] == row.columns[i]}">
> > > evaluates true OK
> > > </c:if>
> > >
> > > <c:if test="${row.columns[i] == row.columns[i+campi]}">
> > > evaluates false even if Strings are identical
> > > </c:if>
> > >
> > > Thank You
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