Asterisk-Java, a free Java library for Asterisk PBX integration, consists of a set of Java classes that allow you to easily build Java applications that interact with an Asterisk PBX Server.

Asterisk-Java supports both interfaces that Asterisk provides for this scenario: The FastAGI protocol and the Manager API.
The FastAGI implementation supports all commands currently available from Asterisk.
The Manager API implementation supports receiving events from the Asterisk server (e.g. call progess, registered peers, channel state) and sending actions to Asterisk (e.g. originate call, agent login/logoff, start/stop voice recording).