Dropwizard: Java framework for developing ops-friendly, RESTful web services

Dropwizard logo

https://dropwizard.github.io/dropwizard/

From the website:

Dropwizard pulls together stable, mature libraries from the Java ecosystem into a simple, light-weight package that lets you focus on getting things done.

Dropwizard has out-of-the-box support for sophisticated configuration, application metrics, logging, operational tools, and much more, allowing you and your team to ship a production-quality web service in the shortest time possible.

Also take a look at this page for a list of the components used in Dropwizard. In short, it uses:
Jetty for HTTP
Jersey for REST
Jackson for JSON
Metrics for metrics
– And a bunch of other tools for logging, templating, database access, et al.

Dropwizard logo

Undertow: Lightweight, non-blocking, embeddable, servlet 3.1 compatible web server with websockets support by JBoss

Undertow Banner

http://undertow.io/

Isn’t that a lovely blog post title?

From the website:

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 3.1 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.

Undertow is sponsored by JBoss and is the default web server in the Wildfly Application Server