I've been working for a bit of time with both SparkJava and some custom command-line tools, and I wanted to have a simple but efficient validation library, so I decided to make one myself.
I just released the v0.2.0, with a concrete documentation, API documentation (Javadoc), and automated CI for tests.
Here's the link: https://gitlab.com/Artemix/validator
I'm open to any suggestion/recommendation that may help me develop this library even further.