JSTL XML Tags
Part 1 | Part 2 | Part 3 | Part 4----------------------------------------------
In this third part of the tutorial on JSTL, the author
explains the use of xml tags of the JSTL and shows their wonderful simplicity
,ease of use and raw power.
----------------------------------------------
No one can have any second opinion about the elegance of
xml tags in JSTL.If the readers have been following the earlier instalments of
this J2EE series of tutorials, they would have come across JAXP,DOM,SAX ,JDOM
and such terms, and it may have been none too easy to learn. But the xml
tags in JSTL , make XML processing and even Transformation , a cynch! And ,we
now proceed to study them.
Making our study
even easier, many of the xml tags in JSTL ,
are very much similar to the 'core' tags. For example, just like
<c:out>, we have <x:out>.
Similarly,
<x:forEach>, <x:if>,<x:when> etc.
So, if we have understood the syntax of the 'core'; tags,
it will not be difficult to use the 'xml' tags.
All the following examples use the books.xml file.It contains 'elements' like 'title' and
'author'..
books.xml
<?xml version="1.0" ?>
<books>
<book>
<title>cobol</title>
<author>roy</author>
</book>
<book>
<title>java</title>
<author>herbert</author>
</book>
<book>
<title>c++</title>
<author>robert</author>
</book>
<book>
<title>coldfusion</title>
<author>allaire</author>
</book>
<book>
<title>xml unleashed</title>
<author>morrison</author>
</book>
<book>
<title>jrun</title>
<author>allaire</author>
</book>
</books>
-----------------------------------------------
demo1
The following program reads the xml file using 'forEach' tag and displays the title and author of each book..
The syntax:
<x:forEach var="n"
select="$doc/books/book">
is used to select the elements from the xml file.
<x:out select="$n/title" />
is used to print the elements of the xml file. We begin
by
importing the reference to the XML file to be parsed.
<c:import url="books.xml" var="url" />
-----
We have given a symbolic name for this file as
'url'.Next we ask
the program to parse this XML file.The resulting tree is given a symbolic
name as 'doc'.
<x:parse
xml="${url}" var="doc" />
In the next step, we direct the program to
demo1.jsp
<%@ page contentType="text/html" %>
<%@ taglib prefix="c"
uri="http://java.sun.com/jstl/core" %>
<%@ taglib prefix="c"
>uri="http://java.sun.com/jstl/xml" %>
<html>
<body>
<c:import url="books.xml" var="url" />
<x:parse
xml="${url}" var="doc" />
-----------------------------------------------<br>
<x:forEach
var="n"
select="$doc/books/book">
<x:out
select="$n/title" />
<br>
<x:out
select="$n/author" />
<br>
========
<br>
</x:forEach>
</body>
</html>
Magically, we have parsed a given XML document and extracted information,
without any mention about DOM,SAX and such words., atall!Wonderful!As a famous author
would say, 'anything that makes my job easier, I like!'.
When we execute the 'program', we get the following
result.
-------------------------------------------
(Result for executing demo1.jsp)
==========================
cobol
roy
==========
java
herbert
==========
c++
robert
==========
coldfusion
allaire
==========
xml unleashed
morrison
==========
jrun
allaire
==========
***********************************************
The following program (demo2)displays the books and authors
of xml file in
table format.
demo2.jsp
<%@ page contentType="text/html" %>
<%@ taglib
prefix="c" uri="http://java.sun.com/jstl/core" %>
<%@ taglib
prefix="c" >uri="http://java.sun.com/jstl/xml" %>
<html>
<body>
<c:import url="books.xml" var="url" />
<x:parse
xml="${url}" var="doc" />
<table border=1>
<th>
<tr>
<td>title</td>
<td>author</td>
</tr>
</th>
<x:forEach
var="n"
select="$doc/books/book">
<td>
<tr> <x:out
select="$n/title" /></tr>
<tr> <x:out
select="$n/author" /></tr>
</td>
</x:forEach>
</table>
</body>
</html>
|
title |
author |
|
cobol |
roy
|
|
java |
herbert |
|
c++
|
robert |
|
coldfusion |
allaire |
|
xml
unleashed |
morrison |
|
jrun |
allaire |
------------------------------------------------
demo3 deals
with the selection of particular book's author
from the xml file ,when we give the title,
with the help of <x:if> action tag.The title
is choosen from combo box in demo2.htm file and
submitted.We get a display of the selected title and its author.
Think of this as an sql query like
"select * from table1 where
title='jrun'"
--------------------------------------------------
demo3.htm
<html>
<body>
SELECT THE
TITLE.<BR>
YOU WILL GET TITLE &
AUTHOR.
<form method=post
action="demo3.jsp">
<select name="combo1">
<option value="xml unleashed">xml
<option value="c++">c++
<option value="coldfusion">cold fusion
<option value="java">java
<option
value="cobol">cobol
</select>
<input type=submit>
</form>
</body>
</html>
--------------------------
demo3.jsp
<%@ page contentType="text/html" %>
<%@ taglib prefix="c"
uri="http://java.sun.com/jstl/core" %>
<%@ taglib prefix="c"
uri="http://java.sun.com/jstl/xml" %>
<html>
<body>
<c:import url="books.xml" var="url" />
<x:parse
xml="${url}" var="doc" />
<c:set var="s" value="${param.combo1}"/>
------
<x:forEach
var="n" select="$doc/books/book" >
<x:if
select="$n/title=$s" >
<x:out select="$n/title" />
<br>
<x:out select="$n/author" />
<br>
</x:if>
</x:forEach>
</body>
</html>
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