Require a service to be active before a bundle is started

Question

I have written a BundleActivator which should update certain configurations before its bundle starts. I need the ConfigurationAdmin service, but I get a null ServiceReference from the BundleContext in the start method of the BundleActivator.

The BundleActivator extends following abstract class and only implements the specific update logic:

public abstract class AbstractConfigUpdater implements BundleActivator {

    private ServiceReference<ConfigurationAdmin> configurationAdminServiceReference;

    @Override
    public void start(final BundleContext context) throws Exception {
        configurationAdminServiceReference = context.getServiceReference(ConfigurationAdmin.class);
        final ConfigurationAdmin configurationAdmin = context.getService(configurationAdminServiceReference);
        final Configuration[] configurations =
                                         configurationAdmin.listConfigurations(getFilter());
        if (configurations != null) {
            for (final Configuration configuration : configurations) {
                final Dictionary<String, Object> properties = configuration.getProperties();
                    if (updateProperties(properties)) {
                    configuration.update(properties);
                }
            }
        }
    }

    protected abstract String getFilter();

    /**
     * Updates the properties if needed.
     *
     * @param properties
     *            the configuration properties
     * @return if any modifications to the Dictionary were made
     */
    protected abstract boolean updateProperties(final Dictionary<String, Object> properties);

    @Override
    public void stop(final BundleContext context) throws Exception {
        context.ungetService(configurationAdminServiceReference);
    }

}

I have added an annotation to the concrete BundleActivator to generate a manifest header to require the ConfigurationAdmin service to be available to the bundle:

@RequireCapability(filter = "(objectClass=org.osgi.service.cm.ConfigurationAdmin)",
               ns = "osgi.service",
               resolution = Resolution.mandatory)

The manifest header is generated, but I still get a null ServiceReference. How should I fix this? Or is there an alternative approach I could take to update configurations before their components are started?

Is there any reason at all not use Declarative Services (DS)? The problem you're trying to solve is really hard in an Activator but trivial in DS. — Peter Kriens
You also confuse static dependencies (Require-Capability) with dynamic dependencies (this bundle should be active). They are two different things and unrelated. The Require Capability ensures there is a bundle installed but there is no guarantee that the service is registered since this can depend on other things. — Peter Kriens
Thanks for the clarification on Require-Capability. The reason I chose a BundleActivator instead of a DS component, is that I want to update configurations on bundle startup, as the ObjectClassDefinition of the configurations has changed and I want to run the configuration update before activation of the corresponding DS components. — Auke te Winkel
Did you look at the OSGi Configurer in R7? (Or its predecessor in v2archive.osgi.enroute/osgi.enroute.configurator.simple.provider). That might solve your problems in an easier way. The way you're going now is a rabbit hole. — Peter Kriens

matteo rulli matteo rulli · Accepted Answer · 2018-09-01T13:46:45

I don't know if this could help, but you can develop a org.osgi.service.cm.ConfigurationPlugin to intercept all the properties that are injected at runtime and modify them:

public class MyConfigurationPlugin implements BundleActivator, ConfigurationPlugin {
    ServiceRegistration<ConfigurationPlugin> configPluginRef;

    @Override
    public void start(BundleContext context) throws Exception {
        //... init the config plugin
        Map<String,String> properties = new HashMap<>();            
        configPluginRef = context.registerService(
            ConfigurationPlugin.class, 
            this, 
            new Hashtable<>(properties));
    }

    @Override
    public void modifyConfiguration(ServiceReference<?> reference,
            Dictionary<String, Object> properties) {
        /*
         * View and possibly modify a set of configuration properties 
         * before they are sent to the Managed Service or the Managed Service Factory.  
         */
    }

}

Of course the Declarative Service approach is a way far simpler option:

@Component ( 
    service= {}, 
    configurationPid={
        configPid1,
        configPid2,
        ...
    })
public class MyComponent {

    @Activate
    public void activate(BundleContext context, Map<String, String> properties) {

    }

    @Modified
    public void updated(BundleContext context, Map<String, String> properties) {
        // Called when properties change
    }
}

but in this case you cannot alter properties values: you can only react to properties changes.

Require a service to be active before a bundle is started

2 Answers