BundleActivator registering resources

Activator.java

package net.nantunes.helloword.one.internal;

import org.osgi.framework.BundleActivator;
import org.osgi.framework.BundleContext;
import org.osgi.framework.ServiceReference;
import org.osgi.service.http.HttpContext;
import org.osgi.service.http.HttpService;
import org.osgi.service.http.NamespaceException;
import org.osgi.util.tracker.ServiceTracker;
import org.osgi.util.tracker.ServiceTrackerCustomizer;

import java.util.Dictionary;
import java.util.Hashtable;

public final class Activator implements BundleActivator,
    ServiceTrackerCustomizer<HttpService, HttpService> {

  private BundleContext bundleContext;

  private ServiceTracker<HttpService, HttpService> tracker;

  /**
   * Called when the OSGi framework starts our bundle
   */
  public void start( BundleContext bc ) throws Exception {
    bundleContext = bc;

    tracker = new ServiceTracker<>( bc, HttpService.class, this );
    tracker.open();
  }

  /**
   * Called when the OSGi framework stops our bundle
   */
  public void stop( BundleContext bc ) throws Exception {
    tracker.close();
  }

  @Override
  public HttpService addingService( ServiceReference<HttpService> reference ) {
    final HttpService httpService = bundleContext.getService( reference );

    if ( httpService != null ) {
      // create a default context to share between registrations
      final HttpContext httpContext = httpService.createDefaultHttpContext();

      // register the hello world servlet
      final Dictionary<String, Object> initParams = new Hashtable<>();
      initParams.put( "from", "HttpService" );
      try {
        // register images as resources
        httpService.registerResources( "/images-1", "/images", httpContext );

        // register alternative alias for images resources
        httpService.registerResources( "/alt-images-1", "/images", httpContext );
      } catch ( NamespaceException e ) {
        e.printStackTrace();
      }
    }
    return httpService;
  }

  @Override
  public void modifiedService( ServiceReference<HttpService> reference, HttpService service ) {
    // ignore
  }

  @Override
  public void removedService( ServiceReference<HttpService> reference, HttpService service ) {
    try {
      service.unregister( "/images-1" );
      service.unregister( "/alt-images-1" );
    } catch ( Exception ignored ) {
    }
  }
}