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125 lines
4.8 KiB
HTML
125 lines
4.8 KiB
HTML
<html>
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<head>
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<title>Smack: Roster and Presence - Jive Software</title>
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<link rel="stylesheet" type="text/css" href="style.css" />
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</head>
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<body>
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<div class="header">
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Roster and Presence
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</div>
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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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The roster lets you keep track of the availability ("presence") of other users.
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A roster also allows you to organize users into groups such as "Friends" and
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"Co-workers". Other IM systems refer to the roster as the buddy list, contact list,
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etc.<p>
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A <tt>Roster</tt> instance is obtained using the <tt>XMPPConnection.getRoster()</tt>
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method, but only after successfully logging into a server.
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<p class="subheader">Roster Entries</p>
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<p>
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Every user in a roster is represented by a RosterEntry, which consists of:<ul>
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<li>An XMPP address (e.g. jsmith@example.com).
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<li>A name you've assigned to the user (e.g. "Joe").
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<li>The list of groups in the roster that the entry belongs to. If the roster
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entry belongs to no groups, it's called an "unfiled entry".
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</ul>
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The following code snippet prints all entries in the roster:
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<pre>
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Roster roster = con.getRoster();
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<b>for</b> (Iterator i=roster.getEntries(); i.hasNext(); ) {
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System.out.println(i.next());
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}
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</pre>
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Methods also exist to get individual entries, the list of unfiled entries, or to get one or
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all roster groups.
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<p class="subheader">Presence</p>
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<img src="images/roster.png" width="166" height="322" vspace="5" hspace="5" alt="Roster" border="0" align="right">
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<p>Every entry in the roster has presence associated with it. The
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<tt>Roster.getPresence(String user)</tt> method will return a Presence object with
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the user's presence or <tt>null</tt> if the user is not online or you are not
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subscribed to the user's presence. <i>Note:</i> typically, presence
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subscription is always tied to the user being on the roster, but this is not
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true in all cases.</p>
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<p>A user either has a presence of online or offline. When a user is online, their
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presence may contain extended information such as what they are currently doing, whether
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they wish to be disturbed, etc. See the Presence class for further details.</p>
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<p class="subheader">Listening for Roster and Presence Changes</p>
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<p>The typical use of the roster class is to display a tree view of groups and entries
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along with the current presence value of each entry. As an example, see the image showing
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a Roster in the Exodus XMPP client to the right.</p>
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<p>The presence information will likely
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change often, and it's also possible for the roster entries to change or be deleted.
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To listen for changing roster and presence data, a RosterListener should be used.
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The following code snippet registers a RosterListener with the Roster that prints
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any presence changes in the roster to standard out. A normal client would use
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similar code to update the roster UI with the changing information.
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<br clear="all">
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<pre>
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final Roster roster = con.getRoster();
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roster.addRosterListener(new RosterListener() {
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<b>public void</b> rosterModified() {
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<font color="gray"><i>// Ignore event for this example.</i></font>
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}
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<b>public void</b> presenceChanged(String user) {
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<font color="gray"><i>// If the presence is unavailable then "null" will be printed,
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// which is fine for this example.</i></font>
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System.out.println(<font color="green">"Presence changed: "</font> + roster.getPresence(user));
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}
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});
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</pre>
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<p class="subheader">Adding Entries to the Roster</p>
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<p>Rosters and presence use a permissions-based model where users must give permission before
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they are added to someone else's roster. This protects a user's privacy by
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making sure that only approved users are able to view their presence information.
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Therefore, when you add a new roster entry it will be in a pending state until
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the other user accepts your request.</p>
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If another user requests a presence subscription so they can add you to their roster,
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you must accept or reject that request. Smack handles presence subscription requests
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in one of three ways: <ul>
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<li> Automatically accept all presence subscription requests.
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<li> Automatically reject all presence subscription requests.
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<li> Process presence subscription requests manually.
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</ul>
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The mode can be set using the <tt>Roster.setSubscriptionMode(int subscriptionMode)</tt>
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method. Simple clients normally use one of the automated subscription modes, while
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full-featured clients should manually process subscription requests and let the
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end-user accept or reject each request. If using the manual mode, a PacketListener
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should be registered that listens for Presence packets that have a type of
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<tt>Presence.Type.SUBSCRIBE</tt>.
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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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