org.ff4j:ff4j-spring-boot-starter (maven):  FF4J, stands for Feature Flipping for Java, helps you implementing the 'feature toggle' agile development practice. Features (services/behaviour/treatments/screen parts) can be enabled and disabled at runtime but also limited to an authorized sub-set of users (e.g : beta-testers for beta feature). Once the feature is enabled and granted you can implement your own strategy to flip through custom FlippingStrategy. 
Keywords: ff4j|flipper|flipping|kotlin-language|spring|springboot