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Clement Escoffier130ca572008-10-13 07:33:03 +00005
Clement Escoffier3e0db1e2009-01-15 15:35:17 +00006 <title>Apache Felix - White Board Pattern Handler</title>
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Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000184<h1><a name="WhiteBoardPatternHandler-Thewhiteboardpatternhandler"></a>The white board pattern handler</h1>
185<p>The objective of this handler is to simplify the development of
186white-board architecture. This architecture-style is based is very
187close to the extender architecture style but use services instead of
Clement Escoffier580d1902009-07-21 12:06:46 +0000188bundles.</p>
189
190<div class="toc">
191<ul>
192 <li><a href="#WhiteBoardPatternHandler-Thewhiteboardpattern">The whiteboard pattern</a></li>
193 <li><a href="#WhiteBoardPatternHandler-Usingthehandler">Using the handler</a></li>
194 <li><a href="#WhiteBoardPatternHandler-Configuration">Configuration</a></li>
195 <li><a href="#WhiteBoardPatternHandler-Configuringthehandlerwithannotations">Configuring the handler with annotations</a></li>
196 <li><a href="#WhiteBoardPatternHandler-Download">Download</a></li>
197</ul></div>
198
199<div class="panelMacro"><table class="infoMacro"><colgroup><col width="24"><col></colgroup><tbody><tr><td valign="top"><img src="white-board-pattern-handler_files/information.gif" alt="" border="0" align="absmiddle" height="16" width="16"></td><td><b>Change in the 1.2.0</b><br><p>The 1.2.0 uses the namespace <tt>org.apache.felix.ipojo.whiteboard</tt> instead of <tt>org.apache.felix.ipojo.white-board-pattern</tt></p></td></tr></tbody></table></div>
200
201<h2><a name="WhiteBoardPatternHandler-Thewhiteboardpattern"></a>The whiteboard pattern</h2>
202<p>A whiteboard is based on two different roles:</p>
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000203<ul>
204 <li>A consumer looking to special services or a services published with a special mark</li>
205 <li>Looked services</li>
206</ul>
Clement Escoffier130ca572008-10-13 07:33:03 +0000207
208
Clement Escoffier580d1902009-07-21 12:06:46 +0000209<p>More information on this pattern is available in this <a href="http://www.osgi.org/wiki/uploads/Links/whiteboard.pdf" rel="nofollow">document</a><br>
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000210Implementing a white board pattern could be complex as the extender
211needs to track these services dynamically. Indeed looked services can
212be highly dynamic; they can arrive, leave or be modified at runtime.<br>
213Several services specified in the OSGi specification use white board pattern such as the Device Access Manager.</p>
214
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000215<h2><a name="WhiteBoardPatternHandler-Usingthehandler"></a>Using the handler</h2>
216<p>First of all, you need to configure the component type to use the handler such as:</p>
Clement Escoffier580d1902009-07-21 12:06:46 +0000217<div class="code">
218<div class="dp-highlighter"><table class="dp-xml" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="tag">&lt;</span><span>ipojo&nbsp;xmlns:</span><span class="attribute">wbp</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.whiteboard"</span><span>&gt;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>component&nbsp;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">className</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.test.FooWhiteBoardPattern"</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>wbp:wbp&nbsp;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">filter</span><span>=</span><span class="attribute-value">"(my.property=1)"</span><span>&nbsp;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">onArrival</span><span>=</span><span class="attribute-value">"onArrival"</span><span>&nbsp;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">onDeparture</span><span>=</span><span class="attribute-value">"onDeparture"</span><span>&nbsp;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="attribute">onModification</span><span>=</span><span class="attribute-value">"onModification"</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">/&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;</span><span>provides</span><span class="tag">/&gt;</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="tag">&lt;/</span><span>component</span><span class="tag">&gt;</span><span>&nbsp;</span></td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="xml:nocontrols:nogutter" rows="10" readonly="readonly">&lt;ipojo xmlns:wbp="org.apache.felix.ipojo.whiteboard"&gt;
Clement Escoffier130ca572008-10-13 07:33:03 +0000219 &lt;component
Clement Escoffier580d1902009-07-21 12:06:46 +0000220 className="org.apache.felix.ipojo.test.FooWhiteBoardPattern"
Clement Escoffier130ca572008-10-13 07:33:03 +0000221 &gt;
222 &lt;wbp:wbp
Clement Escoffier580d1902009-07-21 12:06:46 +0000223 filter="(my.property=1)"
224 onArrival="onArrival"
225 onDeparture="onDeparture"
226 onModification="onModification"
Clement Escoffier130ca572008-10-13 07:33:03 +0000227 /&gt;
228
Clement Escoffier580d1902009-07-21 12:06:46 +0000229 &lt;provides/&gt;
230 &lt;/component&gt;</textarea>
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Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000248<p>Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.whiteboard" namespace.<br>
249Once described, you can implement your component. The methods specified
250methods will be called when a matching services arrives or leaves or
251are modified. The modification callback is optional. A matching service
252is detected by confronting the service reference against the specified
253filter.<br>
254The filter can target specific service interface (with the objectclass property) or property values.<br>
255In the previous example, these methods could be: </p>
Clement Escoffier580d1902009-07-21 12:06:46 +0000256<div class="code">
257<div class="dp-highlighter"><table class="dp-c" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="keyword">public</span><span>&nbsp;</span><span class="keyword">class</span><span>&nbsp;FooWhiteBoardPattern&nbsp;</span><span class="keyword">implements</span><span>&nbsp;Observable&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;List&nbsp;list&nbsp;=&nbsp;new&nbsp;ArrayList();&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;int&nbsp;modifications&nbsp;=&nbsp;0;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">synchronized</span><span>&nbsp;</span><span class="keyword">void</span><span>&nbsp;onArrival(ServiceReference&nbsp;ref)&nbsp;{&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;list.add(ref);&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">synchronized</span><span>&nbsp;</span><span class="keyword">void</span><span>&nbsp;onDeparture(ServiceReference&nbsp;ref)&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;list.remove(ref);&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">synchronized</span><span>&nbsp;</span><span class="keyword">void</span><span>&nbsp;onModification(ServiceReference&nbsp;ref)&nbsp;{&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;modifications&nbsp;=&nbsp;modifications&nbsp;+&nbsp;1;&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">synchronized</span><span>&nbsp;Map&nbsp;getObservations()&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Map&nbsp;map&nbsp;=&nbsp;new&nbsp;HashMap();&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;map.put(<span class="string">"list"</span><span>,&nbsp;list);&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;map.put(<span class="string">"modifications"</span><span>,&nbsp;new&nbsp;Integer(modifications));&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">return</span><span>&nbsp;map;&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;</td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">public class FooWhiteBoardPattern implements Observable {
258 List list = new ArrayList();
259 int modifications = 0;
260 public synchronized void onArrival(ServiceReference ref) {
Clement Escoffier130ca572008-10-13 07:33:03 +0000261 list.add(ref);
262 }
Clement Escoffier580d1902009-07-21 12:06:46 +0000263 public synchronized void onDeparture(ServiceReference ref) {
Clement Escoffier130ca572008-10-13 07:33:03 +0000264 list.remove(ref);
265 }
Clement Escoffier580d1902009-07-21 12:06:46 +0000266 public synchronized void onModification(ServiceReference ref) {
Clement Escoffier130ca572008-10-13 07:33:03 +0000267 modifications = modifications + 1;
268 }
Clement Escoffier580d1902009-07-21 12:06:46 +0000269 public synchronized Map getObservations() {
270 Map map = new HashMap();
271 map.put("list", list);
272 map.put("modifications", new Integer(modifications));
273 return map;
274 }</textarea>
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291
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000292<p>All method received the arriving, leaving or modified service reference.</p>
293<h2><a name="WhiteBoardPatternHandler-Configuration"></a>Configuration</h2>
294<p>The handler has only three mandatory attributes:</p>
295<ul>
296 <li>Filter: filter use to discover matching filter.</li>
297 <li>onArrival: declaring the method to invoke when a matching service arrives</li>
298 <li>onDeparture: declaring the method to invoke when a matching service leaves</li>
299</ul>
Clement Escoffier130ca572008-10-13 07:33:03 +0000300
301
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000302<p>The onModification attribute is optional. This method is called when
303an injected service reference is modified but stills valid against the
304filter.</p>
Clement Escoffier580d1902009-07-21 12:06:46 +0000305<div class="panelMacro"><table class="noteMacro"><colgroup><col width="24"><col></colgroup><tbody><tr><td valign="top"><img src="white-board-pattern-handler_files/warning.gif" alt="" border="0" align="absmiddle" height="16" width="16"></td><td><b>Notifications</b><br><p>The
306implementation will be notified of arrivals, modifications and
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000307departures, despite the instance is invalid. Indeed, the implementation
Clement Escoffier580d1902009-07-21 12:06:46 +0000308must release all objects created from another bundle as soon it leaves.</p></td></tr></tbody></table></div>
309<h2><a name="WhiteBoardPatternHandler-Configuringthehandlerwithannotations"></a>Configuring the handler with annotations</h2>
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000310
311<p>It is possible to configure the handler with a simple annotation
312available in the annotation pack ('annotation' project in the iPOJO
313trunk). Here is an example of usage:</p>
Clement Escoffier580d1902009-07-21 12:06:46 +0000314<div class="code">
315<div class="dp-highlighter"><table class="dp-c" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="keyword">import</span><span>&nbsp;org.apache.felix.ipojo.annotations.Component;&nbsp;</span></td></tr><tr><td class="line2"><span class="keyword">import</span><span>&nbsp;org.osgi.framework.ServiceReference;&nbsp;</span></td></tr><tr><td class="line1"><span class="preprocessor"></span></td></tr><tr><td class="line2"><span class="preprocessor">@Component</span><span>&nbsp;</span></td></tr><tr><td class="line1"><span class="preprocessor">@org.apache.felix.ipojo.whiteboard.Wbp(filter="(foo=true)",&nbsp;</span><span>&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;onArrival=<span class="string">"onArrival"</span><span>,&nbsp;&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;onDeparture=<span class="string">"onDeparture"</span><span>,&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;onModification=<span class="string">"onModification"</span><span>)&nbsp;</span></td></tr><tr><td class="line1"><span class="keyword">public</span><span>&nbsp;</span><span class="keyword">class</span><span>&nbsp;WhiteBoardExemple&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">void</span><span>&nbsp;onArrival(ServiceReference&nbsp;ref)&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;do&nbsp;something</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">void</span><span>&nbsp;onDeparture(ServiceReference&nbsp;ref)&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;do&nbsp;something</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;</td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;<span class="keyword">public</span><span>&nbsp;</span><span class="keyword">void</span><span>&nbsp;onModification(ServiceReference&nbsp;ref)&nbsp;{&nbsp;</span></td></tr><tr><td class="line2">&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<span class="comment">//&nbsp;do&nbsp;something</span><span>&nbsp;</span></td></tr><tr><td class="line1">&nbsp;&nbsp;&nbsp;&nbsp;}&nbsp;</td></tr><tr><td class="line2">&nbsp;</td></tr><tr><td class="line1">}&nbsp;</td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">import org.apache.felix.ipojo.annotations.Component;
316import org.osgi.framework.ServiceReference;
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000317
318@Component
Clement Escoffier580d1902009-07-21 12:06:46 +0000319@org.apache.felix.ipojo.whiteboard.Wbp(filter="(foo=true)",
320 onArrival="onArrival",
321 onDeparture="onDeparture",
322 onModification="onModification")
323public class WhiteBoardExemple {
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000324
Clement Escoffier580d1902009-07-21 12:06:46 +0000325 public void onArrival(ServiceReference ref) {
326 // do something
327 }
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000328
Clement Escoffier580d1902009-07-21 12:06:46 +0000329 public void onDeparture(ServiceReference ref) {
330 // do something
331 }
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000332
Clement Escoffier580d1902009-07-21 12:06:46 +0000333 public void onModification(ServiceReference ref) {
334 // do something
335 }
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000336
Clement Escoffier580d1902009-07-21 12:06:46 +0000337}</textarea>
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Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000355
356<p>The <tt>onModification</tt> attribute is optional.The <tt>filter</tt> attribute allows setting the service filter.</p>
Clement Escoffier130ca572008-10-13 07:33:03 +0000357
Clement Escoffier3e0db1e2009-01-15 15:35:17 +0000358<h2><a name="WhiteBoardPatternHandler-Download"></a>Download</h2>
359<p>The handler is available on the <a href="http://felix.apache.org/site/download.html" title="Download">download</a> page.<br>
Clement Escoffier580d1902009-07-21 12:06:46 +0000360Sources are available on the Felix trunk at the following location: <a href="http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/whiteboard" rel="nofollow">http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/whiteboard</a>.
361<br clear="all">
362<br clear="all"></p>
Clement Escoffier130ca572008-10-13 07:33:03 +0000363
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