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This evening, I took my first dive into XPath, and I have to say, navigating XML documents using JSTL tags and XPath is incredibly easy.<br/>
<br/>
The reason I had to parse an XML document is because one of the features I added for Argus 0.9 was a system that would allow an administrator to upgrade the database easily when deploying a new version of the software. After a successful upgrade, I displayed a list of new features, improvements and bug fixes for that version. What I had envisioned though, is dynamically generating this list, from an XML file.<br/>
<br/>
So how do you use JSTL and XPath to parse your XML document? Well, first off, you have to import and parse your XML file:<br/>
<blockquote>
<code>
<c:import url="changelog.xml" var="url"/><br />
<x:parse xml="${url}" var="changelog"/>
</code>
</blockquote>
After you do this, you now have a parsed XML document that you can start selecting elements from. Let's take a section of my changelog XML to work with.<br/>
<blockquote><div><code><log></code></div><div style="margin-left:10px;"><code><changes version="0.9.2"></code></div><div style="margin-left:20px;"><code><fix>Fixed a changelog email bug while trying to load users with permission.</fix></code></div><div style="margin-left:10px;"><code></changes></code></div>
<div style="margin-left:10px;"><code><changes version="0.9.1"></code></div>
<div style="margin-left:20px;"><code><fix>Hid the 'Assigned to me' scope for regular users.</fix></code></div>
<div style="margin-left:10px;"><code></changes></code></div>
<div style="margin-left:10px;"><code><changes version="0.9"></code></div>
<div style="margin-left:20px;"><code><feature>Upgrade script that can upgrade the database from any older version to the current version.</feature></code></div>
<div style="margin-left:20px;"><code><feature>Personalized ticket scopes added to the filter bar.</feature></code></div>
<div style="margin-left:20px;"><code><improvement>'Revisions' renamed as 'Versions'.</improvement></code></div>
<div style="margin-left:20px;"><code><improvement>Revision live and beta abandoned for simple 'released' flag.</improvement></code></div>
<div style="margin-left:20px;"><code><improvement>Ability to manually set the sort order for Versions.</improvement></code></div>
<div style="margin-left:20px;"><code><improvement>Ability to remove the version selected for a ticket.</improvement></code></div>
<div style="margin-left:20px;"><code><fix>Ticket description no longer gets truncated during an update.</fix></code></div>
<div style="margin-left:10px;"><code></changes></code></div>
<div><code></log></code></div>
</blockquote>
If you want to iterate over all of the the <code>changes</code> elements, you can use the x:forEach tag:<br/>
<blockquote>
<code>
<x:forEach select="$changelog//changes">
</code>
</blockquote>
The key to using XPath syntax, though, is to know where you are in the XML document's DOM. For example, during each iteration, the top level object is a <code>changes</code> element. So your XPath syntax should be relative to that object. Let's say that the first thing we want to do is display the version attribute of the current <code>changes</code> element. We would do:<br/>
<blockquote>
<div style="margin-left:10px;"><code><x:out select="@version"/></code></div>
</blockquote>
Now, what if wanted to iterate over all <code>feature</code> elements that are children of this <code>changes</code> element? Well, we could do something like this:<br/>
<blockquote>
<div style="margin-left:10px;"><code><x:forEach select="./feature"></code></div>
</blockquote>
As you can see, the XPath syntax is pretty straightforward and if you are familiar with navigating a UNIX based operating system, you will see some similarities. A '.' is used to denote the current element and a slash and then an element name means all elements with that name that are children of this node. While inside this x:forEach tag, remember that the current element will be a <code>feature</code> element. If you want to display the contents of each <code>feature</code> element, you would again use x:out like this:<br/>
<blockquote><div style="margin-left:20px;"><code><x:out select="."/></code></div></blockquote>
So, why don't you give it a try. But, don't forget that you'll need to import <code><%@ taglib prefix="x" uri="http://java.sun.com/jsp/jstl/xml" %></code> and have the JSTL jar in your project.
2007-08-14T17:04:15-04:00
This evening, I took my first dive into XPath, and I have to say, navigating XML documents using JSTL tags and XPath is incredibly easy.
1250
2006/06/03/jstl-and-xpath-3
2006-06-04T00:53:00-04:00
jstl-and-xpath-3
JSTL and XPath