2003-01-15 16:03:36 +01:00
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<title>Smack: Packet Properties - Jive Software</title>
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<link rel="stylesheet" type="text/css" href="style.css" /
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<div class="header">
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Packet Properties
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<div class="nav">
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« <a href="index.html">Table of Contents</a>
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</div>
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<p>
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Smack provides an easy mechanism for attaching arbitrary properties to packets. Each property
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has a String name, and a value that is a Java primitive (int, long, float, double, boolean) or
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any Serializable object (a Java object is Serializable when it implements the Serializable
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interface).
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</p>
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<p class="subheader">
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Using the API
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</p>
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<p>
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All major objects have property support, such as Message objects. The following code
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demonstrates how to set properties:
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</p>
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<div class="code"><pre>
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Message message = chat.createMessage();
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<font color="gray"></i>// Add a Color object as a property.</i></font>
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message.setProperty(<font color="blue">"favoriteColor"</font>, new Color(0, 0, 255));
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<font color="gray"></i>// Add an int as a property.</i></font>
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message.setProperty(<font color="blue">"favoriteNumber"</font>, 4);
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chat.sendMessage(message);
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</pre></div>
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<p>
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Getting those same properties would use the following code:
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</p>
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<div class="code"><pre>
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Message message = chat.nextMessage();
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<font color="gray"></i>// Get a Color object property.</i></font>
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Color favoriteColor = (Color)message.getProperty(<font color="blue">"favoriteColor"</font>);
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<font color="gray"></i>// Get an int property. Note that properties are always returned as
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// Objects, so we must cast the value to an Integer, then convert
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// it to an int.</i></font>
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int favoriteNumber = ((Integer)message.getProperty(<font color="blue">"favoriteNumber"</font>)).intValue();
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</pre></div>
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<p class="subheader">
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Objects as Properties
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</p>
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<p>
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Using objects as property values is a very powerful and easy way to exchange data. However,
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you should keep the following in mind:
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</p>
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<ul>
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2003-06-19 20:11:37 +02:00
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<li>Packet extensions are the more standard way to add extra data to XMPP stanzas. Using
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properties may be more convenient in some cases, however, since Smack will do the
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work of handling the XML.
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<li>When you send a Java object as a property, only clients running Java will be able to
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interpret the data. So, consider using a series of primitive values to transfer data
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instead.
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2003-01-15 16:03:36 +01:00
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<li>Objects sent as property values must implement Serialiable. Additionally, both the sender
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and receiver must have identical versions of the class, or a serialization exception
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2003-08-30 16:11:52 +02:00
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will occur when de-serializing the object.
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2003-01-15 16:03:36 +01:00
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<li>Serialized objects can potentially be quite large, which will use more bandwidth and
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server resources.
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</ul>
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<p class="subheader">
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XML Format
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</p>
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<p>
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The current XML format used to send property data is not a standard, so will likely not be
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recognized by clients not using Smack. The XML looks like the following (comments added for
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clarity):
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</p>
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<div class="code"><pre>
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<font color="gray"><i><!-- All properties are in a x block. --></i></font>
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2003-05-08 17:52:43 +02:00
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<properties xmlns="http://www.jivesoftware.com/xmlns/xmpp/properties">
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<font color="gray"><i><!-- First, a property named "prop1" that's an integer. --></i></font>
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<property>
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<name>prop1</name>
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<value type="integer">123</value>
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<property>
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<font color="gray"><i><!-- Next, a Java object that's been serialized and then converted
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from binary data to base-64 encoded text. --></i></font>
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<property>
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<name>blah2</name>
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<value type="java-object">adf612fna9nab</value>
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<property>
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</properties>
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2003-01-15 16:03:36 +01:00
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</pre></div>
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<p>
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The currently supported types are: <tt>integer</tt>, <tt>long</tt>, <tt>float</tt>,
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<tt>double</tt>, <tt>boolean</tt>, <tt>string</tt>, and <tt>java-object</tt>.
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</p>
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<div class="footer">
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Copyright © Jive Software 2002-2003
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</div>
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</body>
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</html>
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