Processing Incoming Stanzas

Smack provides a flexible framework for processing incoming stanzas using two constructs:

org.jivesoftware.smack.StanzaCollector -- a class that lets you synchronously wait for new stanzas.
org.jivesoftware.smack.StanzaListener -- an interface for asynchronously notifying you of incoming stanzas. A stanza listener is used for event style programming, while a stanza collector has a result queue of stanzas that you can do polling and blocking operations on. So, a stanza listener is useful when you want to take some action whenever a stanza happens to come in, while a stanza collector is useful when you want to wait for a specific stanza to arrive. Stanza collectors and listeners can be created using an XMPPConnection instance.

The org.jivesoftware.smack.filter.StanzaFilter interface determines which specific stanzas will be delivered to a StanzaCollector or StanzaListener. Many pre-defined filters can be found in the org.jivesoftware.smack.filter package.

The following code snippet demonstrates registering both a stanza collector and a stanza listener:

// Create a stanza filter to listen for new messages from a particular
// user. We use an AndFilter to combine two other filters._
StanzaFilter filter = new AndFilter(StanzaTypeFilter.Message, FromMatchesFilter.create("mary@jivesoftware.com"));
// Assume we've created an XMPPConnection named "connection".

// First, register a stanza collector using the filter we created.
StanzaCollector myCollector = connection.createStanzaCollector(filter);
// Normally, you'd do something with the collector, like wait for new packets.

// Next, create a stanza listener. We use an anonymous inner class for brevity.
StanzaListener myListener = new StanzaListener() {
		**public** **void** processStanza(Stanza stanza) {
			// Do something with the incoming stanza here._
		}
	};
// Register the listener._
connection.addAsyncStanzaListener(myListener, filter);
// or for a synchronous stanza listener use
connection.addSyncStanzaListener(myListener, filter);

Standard Stanza Filters

A rich set of stanza filters are included with Smack, or you can create your own filters by coding to the StanzaFilter interface. The default set of filters includes:

StanzaTypeFilter -- filters for stanzas that are a particular Class type.
StanzaIdFilter -- filters for stanzas with a particular packet ID.
ThreadFilter -- filters for message stanzas with a particular thread ID.
ToMatchesFilter -- filters for stanzas that are sent to a particular address.
FromMatchesFilter -- filters for stanzas that are sent from a particular address.
StanzaExtensionFilter -- filters for stanzas that have a particular stanza extension.
AndFilter -- implements the logical AND operation over two filters.
OrFilter -- implements the logical OR operation over two filters.
NotFilter -- implements the logical NOT operation on a filter.