Eclipse Jetty - Web Container & Clients - supports HTTP/2, HTTP/1.1, HTTP/1.0, websocket, servlets, and more
Square’s meticulous HTTP client for Java and Kotlin.
Feign makes writing java http clients easier
Type-safe HTTP client for Android and Java by Square, Inc.
Unirest in Java: Simplified, lightweight HTTP client library.
http-kit is a minimalist, event-driven, high-performance Clojure HTTP server/client library with WebSocket and asynchronous support
Asynchronous Java made easier
Fluent Java HTTP client
An asynchronous http client in Java, with a clean, callback-based API, using Netty 4.x