2003-06-19 20:15:28 +02:00
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<title>Smack: Provider Architecture - Jive Software</title>
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Provider Architecture: Packet Extensions and Custom IQ's
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« <a href="index.html">Table of Contents</a>
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<p>
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2003-10-13 19:34:45 +02:00
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The Smack provider architecture is a system for plugging in
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custom XML parsing of packet extensions and IQ packets. The
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standard <a href="extensions/index.html">Smack Extensions</a>
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are built using the provider architecture. Two types of
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providers exist:<ul>
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<li><tt>IQProvider</tt> -- parses IQ requests into Java objects.
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<li><tt>PacketExtension</tt> -- parses XML sub-documents attached to
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packets into PacketExtension instances.</ul>
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<p class="subheader">IQProvider</p>
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By default, Smack only knows how to process IQ packets with sub-packets that
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are in a few namespaces such as:<ul>
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<li>jabber:iq:auth
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<li>jabber:iq:roster
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<li>jabber:iq:register</ul>
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Because many more IQ types are part of XMPP and its extensions, a pluggable IQ parsing
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mechanism is provided. IQ providers are registered programatically or by creating a
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smack.providers file in the META-INF directory of your JAR file. The file is an XML
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document that contains one or more iqProvider entries, as in the following example:
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<pre>
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<?xml version="1.0"?>
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<smackProviders>
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<iqProvider>
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<elementName>query</elementName>
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<namespace>jabber:iq:time</namespace>
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<className>org.jivesoftware.smack.packet.Time</className>
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</iqProvider>
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</smackProviders></pre>
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Each IQ provider is associated with an element name and a namespace. In the
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example above, the element name is <tt>query</tt> and the namespace is
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<tt>abber:iq:time</tt>. If multiple provider entries attempt to register to
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handle the same namespace, the first entry loaded from the classpath will
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take precedence. <p>
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The IQ provider class can either implement the IQProvider
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interface, or extend the IQ class. In the former case, each IQProvider is
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responsible for parsing the raw XML stream to create an IQ instance. In
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the latter case, bean introspection is used to try to automatically set
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properties of the IQ instance using the values found in the IQ packet XML.
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For example, an XMPP time packet resembles the following:
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<pre>
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<iq type='result' to='joe@example.com' from='mary@example.com' id='time_1'>
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<query xmlns='jabber:iq:time'>
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<utc>20020910T17:58:35</utc>
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<tz>MDT</tz>
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<display>Tue Sep 10 12:58:35 2002</display>
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</query>
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</iq></pre>
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In order for this packet to be automatically mapped to the Time object listed in the
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providers file above, it must have the methods setUtc(String), setTz(String), and
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setDisplay(String). The introspection service will automatically try to convert the String
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value from the XML into a boolean, int, long, float, double, or Class depending on the
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type the IQ instance expects.<p>
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<p class="subheader">PacketExtensionProvider</p>
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Packet extension providers provide a pluggable system for
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packet extensions, which are child elements in a custom namespace
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of message and presence packets (IQ packets cannot have packet extensions).
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Each extension provider is registered with an element name and namespace
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in the smack.providers file as in the following example:
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<pre>
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<?xml version="1.0"?>
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<smackProviders>
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<extensionProvider>
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<elementName>x</elementName>
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<namespace>jabber:iq:event</namespace>
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<className>org.jivesoftware.smack.packet.MessageEvent</className>
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</extensionProvider>
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</smackProviders></pre>
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If multiple provider entries attempt to register to handle the same element
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name and namespace, the first entry loaded from the classpath will take
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precedence.<p>
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Whenever a packet extension is found in a packet, parsing will
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be passed to the correct provider. Each provider can either implement the
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PacketExtensionProvider interface or be a standard Java Bean. In the
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former case, each extension provider is responsible for parsing the raw
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XML stream to contruct an object. In the latter case, bean introspection
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is used to try to automatically set the properties of the class using
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the values in the packet extension sub-element.<p>
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When an extension provider is not registered for an element name and
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namespace combination, Smack will store all top-level elements of the
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sub-packet in DefaultPacketExtension object and then attach it to the packet.
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2003-06-19 20:15:28 +02:00
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<br clear="all" /><br><br>
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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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