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 arrive. Packet collectors and listeners can be created using an `XMPPConnection` instance.

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 particular 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.