This document will introduce you to the Smack API and provide an overview of important classes and concepts.
Requirements
The only requirement for Smack is JDK 1.5 or later. An XML parser is embedded in the smack.jar file and no other third party libraries are required.
Establishing a Connection
The XMPPConnection class is used to create a connection to an XMPP server. Below are code examples for making a connection:
// Create a connection to the jabber.org server.
XMPPConnection conn1 = new XMPPConnection("jabber.org");
conn1.connect();
// Create a connection to the jabber.org server on a specific port.
ConnectionConfiguration config = new ConnectionConfiguration("jabber.org", 5222);
XMPPConnection conn2 = new XMPPConnection(config);
conn2.connect();
Note that maximum security will be used when connecting to the server by default (and when possible), including use of TLS encryption. The ConnectionConfiguration class provides advanced control over the connection created, such as the ability to disable or require encryption.
Once you've created a connection, you should login using a username and password with the XMPPConnection.login(String username, String password) method. Once you've logged in, you can being chatting with other users by creating new Chat or GroupChat objects.
Working with the Roster
The roster lets you keep track of the availability (presence) of other users. Users can be organized into groups such as "Friends" and "Co-workers", and then you discover whether each user is online or offline.Retrieve the roster using the XMPPConnection.getRoster() method. The roster class allows you to find all the roster entries, the groups they belong to, and the current presence status of each entry.
Reading and Writing Packets
Each message to the XMPP server from a client is called a packet and is sent as XML. The org.jivesoftware.smack.packet package contains classes that encapsulate the three different basic packet types allowed by XMPP (message, presence, and IQ). Classes such as Chat and GroupChat provide higher-level constructs that manage creating and sending packets automatically, but you can also create and send packets directly. Below is a code example for changing your presence to let people know you're unavailable and "out fishing":
// Create a new presence. Pass in false to indicate we're unavailable.
Presence presence = new Presence(Presence.Type.UNAVAILABLE);
presence.setStatus("Gone fishing");
// Send the packet (assume we have a XMPPConnection instance called "con").
con.sendPacket(presence);
Smack provides two ways to read incoming packets: PacketListener, and PacketCollector. Both use PacketFilter instances to determine which packets should be processed. A packet listener is used for event style programming, while a packet collector has a result queue of packets that you can do polling and blocking operations on. So, a packet listener is useful when you want to take some action whenever a packet happens to come in, while a packet collector is useful when you want to wait for a specific packet to arrive. Packet collectors and listeners can be created using an XMPPConnection instance.