Since about a month I’m developing some microservices using Javalin, a small, simple and lightweight web-framework that started as a fork from SparkJava. By now it’s a ground-up rewrite, influenced by the Javascript framework koa.js. Don’t let the stuff like Either scare you, we use the Arrow library to make our life a bit more easy :)

When requesting user input from a form, it’s evident that we need to validate our input. Javalin has its own way of doing so (from the docs):