HttpAsyncClient Tutorial

http://www.baeldung.com/httpasyncclient-tutorial

https://github.com/eugenp/tutorials/tree/master/httpclient#readme

http://www.programcreek.com/java-api-examples/index.php?api=org.apache.http.impl.nio.client.CloseableHttpAsyncClient

https://hc.apache.org/httpcomponents-asyncclient-dev/examples.html