Vaadin 6, 7, 8 is a Java framework for modern Java web applications.
Leading REST API framework for Java
Lightweight REST for Java
A group of templated API test frameworks based upon this series: http://www.mwtestconsultancy.co.uk/category/api-web-service-testing/
Lightweight Java http server and web application framework.
An example of implementing batch processing using Akka's Java API. This is an adaptation of an idea from http://letitcrash.com/post/29044669086/balancing-workload-across-nodes-with-akka-2
A simple expressive web framework for java. News: Spark now has a kotlin DSL https://github.com/perwendel/spark-kotlin
A Java WebSocket/HTTP server based on the Atmosphere and Netty Framework
Rapidoid - Extremely Fast, Simple and Powerful Java Web Framework and HTTP Server!