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From "Derek Mahar" <DMa...@penson.ca>
Subject RE: [JSTL] Indexed array variable
Date Wed, 02 Jun 2004 14:53:09 GMT
Good question!  We can represent a multi-dimensional array as a
recursive array of arrays.  For example, given tag <c:setArray>, we
could both allocate and assign a two-dimensional array as follows:

<%-- Create the first row, assign it values at index 0 and 1.
<%-- Assign the row to myArray at index 0. --%>
<c:setArray var="row" index="0" value="0"/>
<c:setArray var="row" index="1" value="1"/>
<c:setArray var="myArray" index="0" value="${row}"/>

<%-- Create the second row, assign it values at index 2 and 3.
<%-- Assign the row to myArray at index 0. --%>
<c:setArray var="row" index="0" value="2"/>
<c:setArray var="row" index="1" value="3"/>
<c:setArray var="myArray" index="1" value="${row}"/>

${myArray} now contains [[0,1], [2,3]].

We can use the JSP Expression Language to access each array element so
that

<c:out value="${myArray[0][0]}"/>
<c:out value="${myArray[0][1]}"/>
<c:out value="${myArray[1][1]}"/>
<c:out value="${myArray[1][2]}"/>

outputs

0 1 2 3

Note that each index of 'myArray' refers to a row, each of which is a
one-dimensional array.  By induction, this model extends to
multi-dimensional arrays where each element of an array may refer to
another one-dimensional array whose elements may themselves each refer
to another one-dimensional array, and so on.

What do you think?

Derek

> -----Original Message-----
> From: Simon Benzekri 
> Sent: June 2, 2004 10:10 AM
> To: Tag Libraries Users List
> Subject: RE: [JSTL] Indexed array variable
> 
> 
> Good idea but how will multi-dimensional arrays be populated?
> 
> Simon 
> 
> -----Original Message-----
> From: Helios Alonso [mailto:halonso@atg.com.uy] 
> Sent: Wednesday, June 02, 2004 9:48 AM
> To: Tag Libraries Users List
> Subject: RE: [JSTL] Indexed array variable
> 
> It would be great.  I think it's very appropiate (very common 
> idea even for 
> non-programmers, easy to implement).
> 
> By example (my case):  I want to make a calendar and would 
> like to make it 
> very generical.  If I could use associations with taglibs, I'd make 
> something that gives me dates (or months, weeks, and days), 
> and another 
> bean associating days to properties.  It helps mantaining the 
> calendar code 
> independent from the "properties" code.  And properties could be 
> associations too:
> 
> 'holiday' -> boolean
> 'holidayname' -> name
> 'itemscount' -> int
> 
> and so on.
> 
> The JSP would poduce HTML for the calendar, but guided by the 
> properties of 
> each day (holidays in red, days with items with a link, etc.)
> 
> At 09:25 02/06/2004 -0400, you wrote:
> >I think you're right.  Just like no JSTL tag exists to create an 
> >associative array (a bean or a map indexed by string), no JSTL tag 
> >exists that can explicitly allocate an indexed array.  <jsp:useBean> 
> >can create both associative and indexed arrays, and <c:set> can set 
> >associative array properties, but not indexed array 
> elements.  I think 
> >the only solution, then, is to create my own tag handler similar to 
> ><c:set> that can assign array elements.  Of course, this is 
> >non-standard, but will solve my problem.
> >
> >Will the next version of JSTL enhance <c:set> to permit the 
> assignment 
> >of array elements?
> >
> >Derek
> >
> > > -----Original Message-----
> > > From: Bill Siggelkow [mailto:billsigg@bellsouth.net]
> > > Sent: June 1, 2004 8:49 PM
> > > To: 'Tag Libraries Users List'
> > > Subject: RE: [JSTL] Indexed array variable
> > >
> > >
> > > I don't think that JSTL is going to be able to "create" array 
> > > elements. I think you will need to allocate the array 
> ahead of time. 
> > > Maybe someone else can clarify this a little more.
> > >
> > >
> > > Bill Siggelkow
> > > billsigg@bellsouth.net
> > >
> > >
> > > -----Original Message-----
> > > From: Derek Mahar [mailto:DMahar@penson.ca]
> > > Sent: Tuesday, June 01, 2004 5:10 PM
> > > To: Tag Libraries Users List
> > > Subject: [JSTL] Indexed array variable
> > >
> > > How does one create and assign elements to an indexed 
> array variable 
> > > in JSTL or the Expression Language? <c:set> seems lacking in this 
> > > respect.
> > >
> > > Derek
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