Mobile games development

Some days ago I’ve posted J2ME code to parse RSS feeds using kXML library. Today’s code is about parsing a generic XML, so you can use it to parse any XML document you want. Code is splitted in the following two classes.

XmlNode class

This is the class representing a single node. We’ll define 2 node types:

• Text nodes: nodes without a name, contanining only a textual value. For them we’ll define a TEXT_NODE final variable
• Element nodes: nodes with a tag name, that can have children nodes and/or attributes

XmlNode class source code is available here: XmlNode.java

GenericXmlParser class

This is the class that will actually do XML parsing. We’ll define only one public method, parseXML(), that will accept 2 arguments:

• a KXmlParser instance, that will be used to do XML parsing
• a boolean that will tell if whitespace-only text nodes must be ignored or not

and will return and XmlNode representing the root node of the parsed XML tree.

GenericXmlParser class source code is available here: GenericXmlParser.java

Sample usage

Let’s see how we can use the two classes above. First we must instantiate and initialize a KXmlParser, and then we can call our GenericXmlParser parseXML() method.

InputStreamReader reader = new InputStreamReader(getClass().getResourceAsStream("/test3.xml"));
 
KXmlParser parser = new KXmlParser();
 
parser.setInput(reader);
 
GenericXmlParser gParser = new GenericXmlParser();
 
XmlNode xml = gParser.parseXML(parser, true);

Now, we have our resulting XmlNode that will hold the whole XML tree. We can make a simple dump of it to check if it’s all ok, using this test function:

void dumpXML(XmlNode node, int deep)
{
	for(int i = 0; i < deep; i++)
	{
		System.out.print(" ");
	}
	System.out.print(node.nodeName + " - ");
 
	if(node.nodeValue != null)
	{
		System.out.print("(" + node.nodeValue + ") - ");
	}
	String[] attributes = node.getAttributeNames();
 
	for(int i = 0; i < attributes.length; i++)
	{
		System.out.print(attributes[i] + ": " + node.getAttribute(attributes[i]) + ", ");
	}
 
	System.out.println();
 
	for(int i = 0; i < node.children.size(); i++)
	{
		dumpXML((XmlNode)node.children.elementAt(i), deep + 1);
	}
}

Note: This article is available also on Forum Nokia Wiki: How to parse an XML file in J2ME with kXML

Some days have passed since last J2ME tutorial, so here is a fresh new one!

Today we’ll see how parsing a RSS feed with J2me is easy using KXML library, a fast and small XML pull parser, expecially suited for constrained environments like mobile devices. A live sample, parsing the RSS feed of this blog, is available here.

The detailed explanation of source code is available on my Forum Nokia Wiki article: J2ME RSS Parser with KXml. If you’re interested only in plain source code, you can pick it up here (it includes also the sample midlet you find on the emulator page). To use KXmlRssParser class, you must simply do:

KXmlRssParser parser = new KXmlRssParser();
 
Vector rssItems = parser.parse(yourFeedURL);

and the parse() method will return the complete list of parsed Items, as instances of RssItem class. Source code is of course simplified, for the purpose of this tutorial, as it only considers title, link and description tags of each <item>, but once you understand KXml logic you can extend it, without much effort, to include other infos from RSS feed.

Other resources you might find useful:

• KXML JavaDocs: http://kxml.sourceforge.net/kxml2/javadoc/
• RSS 2.0 Specifications: http://cyber.law.harvard.edu/rss/rss.html