Default activation strategy for a Togglz feature

Question

Since version 2.0.0 Togglz offers Activation Strategies to go with a feature. For instance, you can connect a list of server IP addresses that shall have the feature enabled. However, how are these strategies actually attached to a feature? All I saw was that I can change the strategy in the Togglz console or even edit the data by hand in the database.

What I was looking for is some default mechanism rather similar to @EnabledByDefault. I could implement a custom state repository, it could even look for annotations, but I suspected that this solution existed out of the box.

Answer 1

Just to share my own solution.

An annotation for defaults

I defined annotations that should be used the way @EnabledByDefault is. Here is one for the server-ip strategy:

/**
 * Allows to specify that the annotated feature should use
 * {@link ServerIPStrategy} if the repository doesn't have any
 * state saved.
 * 
 * @author Michael Piefel
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface UsingServerIPStrategy {

    /**
     * A comma-separated list of server IPs for which
     * the feature should be active.
     */
    String value();

}

Using the annotation

In the feature definition, use the annotion like this:

…
@EnabledByDefault
@UsingServerIPStrategy(value = "192.168.1.211")
@Label("Run regular jobs to send status e-mails to participants")
MAIL_CRON_JOBS;
…

State repository to evaluate

I want to take the feature state from a repository if it already has been saved. If not, the annotations must be evaluated. For this, a delegation repository is needed:

/**
 * A Togglz {@link StateRepository} that looks for default strategies
 * on the defined features.
 * 
 * @author Michael Piefel
 */
@AllArgsConstructor
public class DefaultingStateRepository implements StateRepository {

    private StateRepository delegate;

    @Override
    public FeatureState getFeatureState(Feature feature) {
        FeatureState featureState = delegate.getFeatureState(feature);
        if (featureState == null) {
            // Look for a default strategy.
            // If none is defined, a null return value is good enough.
            UsingServerIPStrategy serverIPStrategy = FeatureAnnotations
                    .getAnnotation(feature, UsingServerIPStrategy.class);
            if (serverIPStrategy != null) {
                featureState = new FeatureState(feature,
                        FeatureAnnotations.isEnabledByDefault(feature));
                featureState.setStrategyId(ServerIpActivationStrategy.ID);
                featureState.setParameter(ServerIpActivationStrategy.PARAM_IPS,
                        serverIPStrategy.value());
            }
        }

        return featureState;
    }

    @Override
    public void setFeatureState(FeatureState featureState) {
        // write through
        delegate.setFeatureState(featureState);
    }
}

Wiring is it in

Finally, to use the repository, I wired it in our TogglzConfig component, deferring to JDBC, but letting it be cached as well:

…
@Override
public StateRepository getStateRepository() {
    JDBCStateRepository jdbcStateRepository = new JDBCStateRepository(dataSource);
    DefaultingStateRepository defaultingStateRepository = new
            DefaultingStateRepository(jdbcStateRepository);
    return new CachingStateRepository(defaultingStateRepository, 60_000);
}
…