flexible performant web server written in Java

 Undertow is a flexible performant web server written in Java, providing both
 blocking and non-blocking APIs based on NIO.
 .
 Undertow has a composition based architecture that allows you to build a web
 server by combining small single purpose handlers. This gives you the
 flexibility to choose between a full Java EE servlet 4.0 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.