Curacao is an open-source toolkit for building REST/HTTP-based integration layers on top of asynchronous Servlets.

Curacao 2.6.3 https://github.com/markkolich/curacao

Uses Google's GSON under-the-hood.

See the json method in Benchmarks.java

http://localhost:8080/json

See the plainText method in Benchmarks.java

http://localhost:8080/plaintext