FF4J is a proposition of Feature Toggle. You can enable and disable features through configuration at runtime with dedicated consoles or Web API but also monitor features usage. You can also define any Property and change its value at runtime with the exact same web console.
Try it your self by clicking on the image below :
More information at ff4j.org or reference guide.
<iframe src="//www.slideshare.net/slideshow/embed_code/key/3sZJ9jPsndQGm" width="595" height="485" frameborder="0" marginwidth="0" marginheight="0" scrolling="no" style="border:1px solid #CCC; border-width:1px; margin-bottom:5px; max-width: 100%;" allowfullscreen> </iframe>