In the previous post you could learn how to create a basic custom constraint annotation compatible with the Bean Validation standard. This demo will extend the former post by explaining how to create constraints which are more flexible due to parameters defined for particular use cases. If you’re totally unfamiliar with the topic, I refer you to the aforementioned post to grasp the essentials. Otherwise, just keep reading.
It’s been almost two years since Java 8 was officially released and many excellent articles about new enhancements and related best practices have been written through that time. Surprisingly, one of the more controversial topics amongst all the added features is the Optional class. The type is a container, which can be either empty or contain a non-null value. Such construction reminds the user of an Optional object that the situation when there’s nothing inside must be handled appropriately. Although the definition of the type on Javadoc is quite descriptive, when it comes to identifying valid use cases it’s getting more problematic.
This article has also been published on DZone.