Smack: Processing Incoming Packets

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

org.jivesoftware.smack.PacketCollector -- a class that lets you synchronously wait for new packets.
org.jivesoftware.smack.PacketListener -- an interface for asynchronously notifying you of incoming packets.

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 come through. Packet collectors and listeners can be created using an XMPPConnection object.

The org.jivesoftware.smack.filter.PacketFilter interface determines which specific packets will be delivered to a PacketCollector or PacketListener. Many pre-defined filters can be found in the org.jivesoftware.smack.filter package.

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

// Create a packet filter to listen for new messages from a particular
// user. We use an AndFilter to combine two other filters.
PacketFilter filter = new AndFilter(new PacketTypeFilter(Message.class), 
        new FromContainsFilter("mary@jivesoftware.com"));
// Assume we've created an XMPPConnection name "connection".

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

// Next, create a packet listener. We use an anonymous inner class for brevity.
PacketListener myListener = new PacketListener() {
        public void processPacket(Packet packet) {
            // Do something with the incoming packet here.
        }
    };
// Register the listener.
connection.addPacketListener(myListener, filter);

Standard Packet Filters

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

PacketTypeFilter -- filters for packets that are a particular Class type.
PacketIDFilter -- filters for packets with a particular packet ID.
ThreadFilter -- filters for message packets with a parituclar thread ID.
ToContainsFilter -- filters for packets that are sent to a particular address.
FromContainsFilter -- filters for packets that are sent to a particular address.
PacketExtensionFilter -- filters for packets that have a particular packet 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.