Smack: Getting Started - Jive Software

This document will introduce you to the Smack API and provide an overview of important classes and concepts.

JAR Files and Requirements

Smack is meant to be easily embedded into any existing JDK 1.5 or later Java application. It has no external dependencies (except for the Jingle voice chat functionality) and is optimized to be as small as possible. The library ships as several JAR files to provide more flexibility over which features applications require:

smack-core.jar -- provides core XMPP functionality. All XMPP features that are part of the XMPP RFCs are included.
smack-extensions.jar -- support for many of the extensions (XEPs) defined by the XMPP Standards Foundation, including multi-user chat, file transfer, user search, etc. The extensions are documented in the extensions manual.
smack-experimental.jar -- support for experimental extensions (XEPs) defined by the XMPP Standards Foundation. The API and functionality of those extensions should be considered as unstable.
smack-legacy.jar -- support for legacy extensions (XEPs) defined by the XMPP Standards Foundation.
smack-bosh.jar -- support for BOSH (XEP-0124). This code should be considered as beta.
smack-jingle.jar -- support for Jingle. This code is old and currenlty unmaintained.
smack-resolver-dnsjava.jar -- support for resolving DNS SRV records with the help of dnsjava. Ideal for platforms that do not support the javax.naming API.
smack-resolver-javax.jar -- support for resolving DNS SRV records with the javax namespace API.
smack-debug.jar -- an enhanced GUI debugger for protocol traffic. It will automatically be used when found in the classpath and when debugging is enabled.

Configuration

Smack has an initialization process that involves 2 phases.

Initializing system properties - Initializing all the system properties accessible through the class SmackConfiguration. These properties are retrieve by the getXXX methods on that class.
Initializing startup classes - Initializing any classes meant to be active at startup by instantiating the class, and then calling the initialize method on that class if it extends SmackInitializer. If it does not extend this interface, then initialization will have to take place in a static block of code which is automatically executed when the class is loaded.

Initialization is accomplished via a configuration file. By default, Smack will load the one embedded in the Smack jar at org.jivesoftware.smack/smack-config.xml. This particular configuration contains a list of initializer classes to load. All manager type classes that need to be initialized are contained in this list of initializers.

Establishing a Connection

The classes subclassing AbstractXMPPConnection are 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.
AbstractXMPPConnection conn1 = new XMPPTCPConnection("jabber.org");
conn1.connect();

// Create a connection to the jabber.org server on a specific port.
ConnectionConfiguration config = new ConnectionConfiguration("jabber.org", 5222);
AbstractXMPPConnection conn2 = new XMPPTCPConnection(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. See XMPPConnection Management for full details.

Once you've created a connection, you should login using a username and password with the AbstractXMPPConnection.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 AbstractXMPPConnection 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 Connection instance.