Smack provides an easy mechanism for attaching arbitrary properties to packets. Each property has a String name, and a value that is a Java primitive (int, long, float, double, boolean) or any Serializable object (a Java object is Serializable when it implements the Serializable interface).
Using the API
All major objects have property support, such as Message objects. The following code demonstrates how to set properties:
Message message = chat.createMessage(); // Add a Color object as a property. message.setProperty("favoriteColor", new Color(0, 0, 255)); // Add an int as a property. message.setProperty("favoriteNumber", 4); chat.sendMessage(message);
Getting those same properties would use the following code:
Message message = chat.nextMessage(); // Get a Color object property. Color favoriteColor = (Color)message.getProperty("favoriteColor"); // Get an int property. Note that properties are always returned as // Objects, so we must cast the value to an Integer, then convert // it to an int. int favoriteNumber = ((Integer)message.getProperty("favoriteNumber")).intValue();
Objects as Properties
Using objects as property values is a very powerful and easy way to exchange data. However, you should keep the following in mind:
The current XML format used to send property data is not a standard, so will likely not be recognized by clients not using Smack. The XML looks like the following (comments added for clarity):
<!-- All properties are in a x block. --> <properties xmlns="http://www.jivesoftware.com/xmlns/xmpp/properties"> <!-- First, a property named "prop1" that's an integer. --> <property> <name>prop1</name> <value type="integer">123</value> <property> <!-- Next, a Java object that's been serialized and then converted from binary data to base-64 encoded text. --> <property> <name>blah2</name> <value type="java-object">adf612fna9nab</value> <property> </properties>
The currently supported types are: integer, long, float, double, boolean, string, and java-object.