In cases where there is no incoming request, you can retrieve a registered OSGi service through the current class' BundleContext. Provide ServiceUtil.getService() with the class of the service you wish to retrieve.

ServiceUtil.java

/**
 * Methods for interacting with services.
 */
public final class ServiceUtil {

    private ServiceUtil() {

        // private constructor for utility class

    }

    /**
     * Get a service from the bundle context of given service class.
     *
     * @param serviceClass  Class of service to retrieve from bundle context.
     * @param <T>   Type of service to retrieve.
     *
     * @return  Requested service or null if it was not found.
     */
    public static <T> T getService(final Class<T> serviceClass) {

        final BundleContext bundleContext = FrameworkUtil.getBundle(serviceClass).getBundleContext();
        final ServiceReference serviceReference = bundleContext.getServiceReference(serviceClass.getName());

        if (serviceReference != null) {

            // return service class
            return serviceClass.cast(bundleContext.getService(serviceReference));

        } else {

            throw new IllegalArgumentException("No service registered for class " + serviceClass.getName());

        }

    }

}