If you’re an impatient kind, here’s the source code.

I created the project  in Eclipse, instructions here.

Now, let’s start off with a “repository customizer” which is Nexus extension point we’ll use to insert a custom request processor into every repository…

public class GaTrackerRepositoryCustomizer implements RepositoryCustomizer {

    private final Logger log = LoggerFactory.getLogger(getClass());

    @Inject
    @Named("gaTracker")
    private RequestProcessor gaTracker;

    @Override
    public void configureRepository(Repository rep) throws ConfigurationException {
        log.debug("Attaching tracker to: " + rep.getName());
        rep.getRequestProcessors().put("gaTracker", gaTracker);
    }

    @Override
    public boolean isHandledRepository(Repository rep) {
        boolean b = true;
        log.info("Handles repository '" + rep.getName() + "': " + b);
        return b;
    }
}

Not too complicated. We’re using injection to get hold of the actual tracker components and we’re inserting it into all repostories.

Wait, all repositories? Yes, and it’s problem I haven’t really figured out yet. Ideally I’d like to track “hosted” repositories only. However, we’ve configured all our builds to use a few common development “groups” for convenience. However, Nexus seems to treat groups as first class members, so even though an artifact may be deployed in a hosted repository while accessed through a group, the request processor will not get notified for the hosted repository, only the group. I tend to see “groups” as equivalent to “views” in which case I’d expect the hosted repository to be called as well, but, no…

Now, let’s create a request processor which will react when someone “reads” a path in a repository.  We’ll take it in pieces…

@Named("gaTracker")
public class GaTrackerRequestProcessor implements RequestProcessor {

    public static final String GA_TRACKER_ID =
        System.getProperty("cubeia.nexus.gaTrackerId");
    public static final String GA_REFERER_URL =
        System.getProperty("cubeia.nexus.gaRefererUrl");

    private final Logger log = LoggerFactory.getLogger(getClass());
    private final JGoogleAnalyticsTracker tracker;

    public GaTrackerRequestProcessor() {
        if(GA_TRACKER_ID == null) {
            String msg = "Missing system property 'cubeia.nexus.gaTrackerId'";
            throw new IllegalStateException(msg);
        }
         log.info("Creating new tracker, with id: " + GA_TRACKER_ID);
        tracker = new JGoogleAnalyticsTracker("nexus", "read", GA_TRACKER_ID);
        checkRefererUrl();
        adaptLogging();
    }

    [...]

We configure the plugin via system properties (not too beautiful, I know), the “tracker id” is the google tracking code id and is mandatory, and the “refer url” will be set on the call to GA if available.  We’re using the JGoogleAnalytics library to call GA for us. Also, I’m being naughty and throwing an illegal state exception if the tracker id is missing, since GA updates every 24 hours we’d like to be notified on errors early.

There’s  two methods above, one sets the logging in the tracker code to use to slf4j logger instead and the other checks for and sets the referer URL:

private void adaptLogging() {
    /*
     * Adapt the logging to use slf4j instead.
     */
    tracker.setLoggingAdapter(new LoggingAdapter() {

        public void logMessage(String msg) {
            log.debug(msg);
        }

        public void logError(String msg) {
            log.error(msg);
        }
    });
}

private void checkRefererUrl() {
    if(GA_REFERER_URL != null) {
        /*
         * If we have a referer URL we need to set this. However, the
         * tracker does not have a getter for the URL binding strategy, so
         * we'll simply create a new one, ugly, but works.
         */
        log.info("Modifying GA tracking to use referer URL: " + GA_REFERER_URL);
        GoogleAnalytics_v1_URLBuildingStrategy urlb;
        urlb = new GoogleAnalytics_v1_URLBuildingStrategy("nexus", "read", GA_TRACKER_ID);
        urlb.setRefererURL("http://m2.cubeia.com");
        // set new referer
        tracker.setUrlBuildingStrategy(urlb);
    }
}

Not too complicated eh? The only thing to note is that the only way to set the refer URL isby creating a new URL building strategy. Well, I can live with that.

Before we go on we’ll create a small subclass on FocusPoint which we’ll use for tracking. Since JGoogleAnalitycs is made primarily for applications the focus point will URL encode itself, however, that won’t work for us, so we need to override it’s getContentURI method:

/**
 * Simple inner class that adapts the content URI to
 * not be URL-escaped.
 */
private static class Point extends FocusPoint {

    public Point(String name) {
        super(name);
    }

    @Override
    public String getContentURI() {
        return getName();
    }
}

And finally we’ll tie it all toghether. We’ll react on “read” actions, create a URI (of form ‘//path’) and track asynchronously (which will spawn a new thread for calling GA:

 public boolean process(Repository rep, ResourceStoreRequest req, Action action) {
    if(action == Action.read) {
        /*
         * 1) create path by appending repo path to repo id
         * 2) create a subclass of focus point that handles proper URI's
         * 3) track asynchronously, this will perform the tracking on a new thread
         */
        String path = rep.getId() + req.getRequestPath();
        log.debug("Tracking path: " + path);
        FocusPoint p = new Point(path);
        tracker.trackAsynchronously(p);
    } else {
        log.debug("Ingoring action '" + action + "' for: " + req.getRequestPath());
    }
    return true;
}

And that’s it. It’s not perfect though ideally I’d like to track hosted repositories only, I’d like to avoid tracking crawlers and I would prefer not to configure via system properties (hint for you Nexus bundle users out there, you can set system properties in the “conf/wrapper.conf” files), but I’ll leave those for a rainy day.

Here’s the source code as a Maven project.

Enjoy!

Update: If you download and try to compile, you will probably be missing the JGoogleAnalytics lib. You’re welcome to use our, GA-tracked, repository if you like

<repository>
  <id>cubeia-nexus</id>
  <url>http://m2.cubeia.com/nexus/content/groups/public/</url>
  <releases>
    <enabled>true</enabled>
  </releases>
  <snapshots>
    <enabled>true</enabled>
  </snapshots>
</repository>