For the launch of Wooki, we wanted to track our visitors to have some feedback about their use of the website.

To achieve that, we implemented a transparent service that automatically adds Google Analytics scripts to the end of pages. This can be easily done using the MarkupWriter and manipulating the generated Document.

Declaring a new MarkupRendererFilter

To indirectly manipulate the generated Document, we chose to create a new MarkupRendererFilter named “GAnalyticsScriptInjector”. Theses filter are dedicated to code execution before and/or after the main rendering process.

In our case, we wanted to add the script only when the application was in “production mode” and after the rendering process.

com.spreadthesource.tapestry.ganalytics.services.GAnalyticsModule

	public void contributeMarkupRenderer(OrderedConfiguration<MarkupRendererFilter> configuration,
			@Symbol(SymbolConstants.PRODUCTION_MODE) final boolean productionMode) {

		if (productionMode) {
			configuration.addInstance("GAnalyticsScript", GAnalyticsScriptsInjector.class, "after:RenderSupport");
		}

	}

Script injector filter

The filter just needed to add a script in the page. We added a Symbol to make this filter more configurable: the Google Analytics key can be provided by your AppModule, in a web.xml, in a properties file, or as a JVM argument.

com.spreadthesource.tapestry.ganalytics.services.GAnalyticsScriptsInjector

public class GAnalyticsScriptsInjector implements MarkupRendererFilter {

	private final static Messages SCRIPTS = MessagesImpl.forClass(GAnalyticsScriptsMessages.class);

	private final String key;

	public GAnalyticsScriptsInjector(@Inject @Symbol(GAnalyticsConstants.GANALYTICS_KEY) String key) {
		this.key = key;
	}

	private void addScript(Document document) {
		if (key != null && !key.trim().equals("")) {
			Element root = document.getRootElement();

			if (root == null)
				return;

			Element body = root.find("body");

			if (body == null) {
				body = root.element("body");
			}

			Element e = body.element("script", "type", "text/javascript");

			e.raw(SCRIPTS.get("scriptOne"));

			e = body.element("script", "type", "text/javascript");

			e.raw(SCRIPTS.format("scriptTwo", key));

		}
	}

	public void renderMarkup(MarkupWriter writer, MarkupRenderer renderer) {
		renderer.renderMarkup(writer);

		this.addScript(writer.getDocument());
	}

}

Finalisation

We said that we made possible to configure the Google Analytics key, so we created an interface to store the constant valued to the key symbol.

com.spreadthesource.tapestry.ganalytics.GAnalyticsConstants

public interface GAnalyticsConstants {
public static final String GANALYTICS_KEY = "ganalytics.key";
}

To get the Google Analytics scripts, we used the facility provided by “Messages.forClass()”: you just have to create a class which names ends by “Messages” and Tapestry will automatically load the catalog messages corresponding to yourClassNameStrings.

com.spreadthesource.tapestry.ganalytics.GAnalyticsScriptsMessages

public class GAnalyticsScriptsMessages {

}

com.spreadthesource.tapestry.ganalytics.GAnalyticsScriptsStrings.properties

scriptOne=var gaJsHost = (("https:" == document.location.protocol) ? "https://ssl." : "http://www.");\n \
document.write(unescape("%3Cscript src='" + gaJsHost + "google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
scriptTwo=try { \n\
var pageTracker = _gat._getTracker("%s");\n\
pageTracker._trackPageview();\n\
} catch(err) {}

We also contributed to the “factory defaults” in order to declare the Symbol:

com.spreadthesource.tapestry.ganalytics.services.GAnalyticsModule

public static void contributeFactoryDefaults(MappedConfiguration<String, String> configuration) {
configuration.add(GAnalyticsConstants.GANALYTICS_KEY, "");
}

Check out the source code on Github!

This feature has been extracted from Wooki and is available as a standalone project. You just have to include it as a dependency into your own project. Download it now from :

http://github.com/robink/tap-ganalytics/

Let the magic happen

We use Jetty webserver to host Wooki in production. We edited the webdefault.xml file and added this:

<context-param>
<param-name>ganalytics.key<param-name>
<param-value>UA-dummyGA-foo</param-value>
</context-param>

So now, every time we will add a project that include our library as a dependency, Google Analytics code will be added. No more configuration, no declaration in our project, just a dependency. And that last thing is really awesome. :)