Spark Framework

Spark Framework (a pure Java technique to create REST APIs fast)
http://sparkjava.com

Good, Related Article
https://www.boxuk.com/insight/blog-posts/creating-rest-api-quickly-using-pure-java

Open API Initiative (was Swagger)

Open API Initiative Github Base Link:
https://github.com/OAI

Swagger Online Editor
http://editor.swagger.io