2) The Jabber voice/video SDK is a JavaScript library intended for use in PC browser-based applications. If you are looking for Java-specific way to integrate with Jabber IM & Presence, you will likely need to investigate a 3rd party XMPP stack/library. A listing can be found here: https://xmpp.org/software/libraries.html though note that Cisco does not directly recommend/support any particular XMPP library.
3) This walk-through has some details on basic IM & P event plumbing which should get you started: