Activator.java

package example_bundle;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.util.tracker.ServiceTracker;
import org.osgi.service.prefs.PreferencesService;
import org.osgi.service.prefs.Preferences;

public class Activator implements BundleActivator {

  private ServiceTracker      tracker;

  private PreferencesService  service;

  private static final String COLOR = "color"; // NON-NLS-1

  /**
   * {@inheritDoc}
   */
  public void start(BundleContext context) throws Exception {
    tracker = new ServiceTracker(context, PreferencesService.class.getName(), null);
    tracker.open();

    // grab the service
    service = (PreferencesService) tracker.getService();
    Preferences preferences = service.getSystemPreferences();

    preferences.put(COLOR, "lavender");
    // org.osgi.service.url.URLStreamHandlerService urlStreamHandlerService = null;
    System.out.println("My favourite color is: " + preferences.get(COLOR, ""));
  }

  /**
   * {@inheritDoc}
   */
  public void stop(BundleContext context) throws Exception {
    // clean up
    tracker.close();
    tracker = null;

    service = null;
  }

}