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.
a curl-inspired but java based http command line client
Java HTTP Request Library
http-kit is a minimalist, event-driven, high-performance Clojure HTTP server/client library with WebSocket and asynchronous support
The Grizzly Async Http Client (GAHC) library purpose is to allow Java applications to easily execute HTTP requests and asynchronously process the HTTP responses
Fast Parallel Async HTTP/SSH/TCP/UDP/Ping Client Java Library. Aggregate 100,000 APIs & send anywhere in 20 lines of code. Ping/HTTP Calls 8000 servers in 12 seconds. (Akka) www.parallec.io
An asynchronous http client in Java, with a clean, callback-based API, using Netty 4.x