Undertow is a flexible performant web server written in java, providing both blocking and non-blocking API’s based on NIO.

Undertow has a composition based architecture that allows you to build a web server by combining small single purpose handlers. The gives you the flexibility to choose between a full Java EE servlet container, or a low level non-blocking handler, to anything in between.

Undertow is designed to be fully embeddable, with easy to use fluent builder APIs. Undertow’s lifecycle is completely controlled by the embedding application.

GitHub: https://github.com/undertow-io/undertow