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| <h1><a name="WhiteBoardPatternHandler-Thewhiteboardpatternhandler"></a>The white board pattern handler</h1> |
| <p>The objective of this handler is to simplify the development of |
| white-board architecture. This architecture-style is based is very |
| close to the extender architecture style but use services instead of |
| bundles.</p> |
| |
| <div class="toc"> |
| <ul> |
| <li><a href="#WhiteBoardPatternHandler-Thewhiteboardpattern">The whiteboard pattern</a></li> |
| <li><a href="#WhiteBoardPatternHandler-Usingthehandler">Using the handler</a></li> |
| <li><a href="#WhiteBoardPatternHandler-Configuration">Configuration</a></li> |
| <li><a href="#WhiteBoardPatternHandler-Configuringthehandlerwithannotations">Configuring the handler with annotations</a></li> |
| <li><a href="#WhiteBoardPatternHandler-Download">Download</a></li> |
| </ul></div> |
| |
| <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> |
| |
| <h2><a name="WhiteBoardPatternHandler-Thewhiteboardpattern"></a>The whiteboard pattern</h2> |
| <p>A whiteboard is based on two different roles:</p> |
| <ul> |
| <li>A consumer looking to special services or a services published with a special mark</li> |
| <li>Looked services</li> |
| </ul> |
| |
| |
| <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> |
| Implementing a white board pattern could be complex as the extender |
| needs to track these services dynamically. Indeed looked services can |
| be highly dynamic; they can arrive, leave or be modified at runtime.<br> |
| Several services specified in the OSGi specification use white board pattern such as the Device Access Manager.</p> |
| |
| <h2><a name="WhiteBoardPatternHandler-Usingthehandler"></a>Using the handler</h2> |
| <p>First of all, you need to configure the component type to use the handler such as:</p> |
| <div class="code"> |
| <div class="dp-highlighter"><table class="dp-xml" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="tag"><</span><span>ipojo xmlns:</span><span class="attribute">wbp</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.whiteboard"</span><span>> </span></td></tr><tr><td class="line2"> <span class="tag"><</span><span>component </span></td></tr><tr><td class="line1"> <span class="attribute">className</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.test.FooWhiteBoardPattern"</span><span> </span></td></tr><tr><td class="line2"> <span class="tag">></span><span> </span></td></tr><tr><td class="line1"> <span class="tag"><</span><span>wbp:wbp </span></td></tr><tr><td class="line2"> <span class="attribute">filter</span><span>=</span><span class="attribute-value">"(my.property=1)"</span><span> </span></td></tr><tr><td class="line1"> <span class="attribute">onArrival</span><span>=</span><span class="attribute-value">"onArrival"</span><span> </span></td></tr><tr><td class="line2"> <span class="attribute">onDeparture</span><span>=</span><span class="attribute-value">"onDeparture"</span><span> </span></td></tr><tr><td class="line1"> <span class="attribute">onModification</span><span>=</span><span class="attribute-value">"onModification"</span><span> </span></td></tr><tr><td class="line2"> <span class="tag">/></span><span> </span></td></tr><tr><td class="line1"> </td></tr><tr><td class="line2"> <span class="tag"><</span><span>provides</span><span class="tag">/></span><span> </span></td></tr><tr><td class="line1"> <span class="tag"></</span><span>component</span><span class="tag">></span><span> </span></td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="xml:nocontrols:nogutter" rows="10" readonly="readonly"><ipojo xmlns:wbp="org.apache.felix.ipojo.whiteboard"> |
| <component |
| className="org.apache.felix.ipojo.test.FooWhiteBoardPattern" |
| > |
| <wbp:wbp |
| filter="(my.property=1)" |
| onArrival="onArrival" |
| onDeparture="onDeparture" |
| onModification="onModification" |
| /> |
| |
| <provides/> |
| </component></textarea> |
| <script class="javascript"> |
| if(!window.newcodemacro_initialised) |
| { |
| window.newcodemacro_initialised = true; |
| window.oldonloadmethod = window.onload; |
| window.onload = function(){ |
| dp.SyntaxHighlighter.HighlightAll('newcodemacro'); |
| if(window.oldonloadmethod) |
| { |
| window.oldonloadmethod(); |
| } |
| } |
| } |
| |
| </script> |
| </div> |
| |
| <p>Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.whiteboard" namespace.<br> |
| Once described, you can implement your component. The methods specified |
| methods will be called when a matching services arrives or leaves or |
| are modified. The modification callback is optional. A matching service |
| is detected by confronting the service reference against the specified |
| filter.<br> |
| The filter can target specific service interface (with the objectclass property) or property values.<br> |
| In the previous example, these methods could be: </p> |
| <div class="code"> |
| <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> </span><span class="keyword">class</span><span> FooWhiteBoardPattern </span><span class="keyword">implements</span><span> Observable { </span></td></tr><tr><td class="line2"> List list = new ArrayList(); </td></tr><tr><td class="line1"> int modifications = 0; </td></tr><tr><td class="line2"> <span class="keyword">public</span><span> </span><span class="keyword">synchronized</span><span> </span><span class="keyword">void</span><span> onArrival(ServiceReference ref) { </span></td></tr><tr><td class="line1"> list.add(ref); </td></tr><tr><td class="line2"> } </td></tr><tr><td class="line1"> <span class="keyword">public</span><span> </span><span class="keyword">synchronized</span><span> </span><span class="keyword">void</span><span> onDeparture(ServiceReference ref) { </span></td></tr><tr><td class="line2"> list.remove(ref); </td></tr><tr><td class="line1"> } </td></tr><tr><td class="line2"> <span class="keyword">public</span><span> </span><span class="keyword">synchronized</span><span> </span><span class="keyword">void</span><span> onModification(ServiceReference ref) { </span></td></tr><tr><td class="line1"> modifications = modifications + 1; </td></tr><tr><td class="line2"> } </td></tr><tr><td class="line1"> <span class="keyword">public</span><span> </span><span class="keyword">synchronized</span><span> Map getObservations() { </span></td></tr><tr><td class="line2"> Map map = new HashMap(); </td></tr><tr><td class="line1"> map.put(<span class="string">"list"</span><span>, list); </span></td></tr><tr><td class="line2"> map.put(<span class="string">"modifications"</span><span>, new Integer(modifications)); </span></td></tr><tr><td class="line1"> <span class="keyword">return</span><span> map; </span></td></tr><tr><td class="line2"> } </td></tr></tbody></table></div><textarea style="display: none;" name="newcodemacro" class="java:nocontrols:nogutter" rows="10" readonly="readonly">public class FooWhiteBoardPattern implements Observable { |
| List list = new ArrayList(); |
| int modifications = 0; |
| public synchronized void onArrival(ServiceReference ref) { |
| list.add(ref); |
| } |
| public synchronized void onDeparture(ServiceReference ref) { |
| list.remove(ref); |
| } |
| public synchronized void onModification(ServiceReference ref) { |
| modifications = modifications + 1; |
| } |
| public synchronized Map getObservations() { |
| Map map = new HashMap(); |
| map.put("list", list); |
| map.put("modifications", new Integer(modifications)); |
| return map; |
| }</textarea> |
| <script class="javascript"> |
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| |
| </script> |
| </div> |
| |
| <p>All method received the arriving, leaving or modified service reference.</p> |
| <h2><a name="WhiteBoardPatternHandler-Configuration"></a>Configuration</h2> |
| <p>The handler has only three mandatory attributes:</p> |
| <ul> |
| <li>Filter: filter use to discover matching filter.</li> |
| <li>onArrival: declaring the method to invoke when a matching service arrives</li> |
| <li>onDeparture: declaring the method to invoke when a matching service leaves</li> |
| </ul> |
| |
| |
| <p>The onModification attribute is optional. This method is called when |
| an injected service reference is modified but stills valid against the |
| filter.</p> |
| <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 |
| implementation will be notified of arrivals, modifications and |
| departures, despite the instance is invalid. Indeed, the implementation |
| must release all objects created from another bundle as soon it leaves.</p></td></tr></tbody></table></div> |
| <h2><a name="WhiteBoardPatternHandler-Configuringthehandlerwithannotations"></a>Configuring the handler with annotations</h2> |
| |
| <p>It is possible to configure the handler with a simple annotation |
| available in the annotation pack ('annotation' project in the iPOJO |
| trunk). Here is an example of usage:</p> |
| <div class="code"> |
| <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> org.apache.felix.ipojo.annotations.Component; </span></td></tr><tr><td class="line2"><span class="keyword">import</span><span> org.osgi.framework.ServiceReference; </span></td></tr><tr><td class="line1"><span class="preprocessor"></span></td></tr><tr><td class="line2"><span class="preprocessor">@Component</span><span> </span></td></tr><tr><td class="line1"><span class="preprocessor">@org.apache.felix.ipojo.whiteboard.Wbp(filter="(foo=true)", </span><span> </span></td></tr><tr><td class="line2"> onArrival=<span class="string">"onArrival"</span><span>, </span></td></tr><tr><td class="line1"> onDeparture=<span class="string">"onDeparture"</span><span>, </span></td></tr><tr><td class="line2"> onModification=<span class="string">"onModification"</span><span>) </span></td></tr><tr><td class="line1"><span class="keyword">public</span><span> </span><span class="keyword">class</span><span> WhiteBoardExemple { </span></td></tr><tr><td class="line2"> </td></tr><tr><td class="line1"> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> onArrival(ServiceReference ref) { </span></td></tr><tr><td class="line2"> <span class="comment">// do something</span><span> </span></td></tr><tr><td class="line1"> } </td></tr><tr><td class="line2"> </td></tr><tr><td class="line1"> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> onDeparture(ServiceReference ref) { </span></td></tr><tr><td class="line2"> <span class="comment">// do something</span><span> </span></td></tr><tr><td class="line1"> } </td></tr><tr><td class="line2"> </td></tr><tr><td class="line1"> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> onModification(ServiceReference ref) { </span></td></tr><tr><td class="line2"> <span class="comment">// do something</span><span> </span></td></tr><tr><td class="line1"> } </td></tr><tr><td class="line2"> </td></tr><tr><td class="line1">} </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; |
| import org.osgi.framework.ServiceReference; |
| |
| @Component |
| @org.apache.felix.ipojo.whiteboard.Wbp(filter="(foo=true)", |
| onArrival="onArrival", |
| onDeparture="onDeparture", |
| onModification="onModification") |
| public class WhiteBoardExemple { |
| |
| public void onArrival(ServiceReference ref) { |
| // do something |
| } |
| |
| public void onDeparture(ServiceReference ref) { |
| // do something |
| } |
| |
| public void onModification(ServiceReference ref) { |
| // do something |
| } |
| |
| }</textarea> |
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| |
| </script> |
| </div> |
| |
| |
| <p>The <tt>onModification</tt> attribute is optional.The <tt>filter</tt> attribute allows setting the service filter.</p> |
| |
| <h2><a name="WhiteBoardPatternHandler-Download"></a>Download</h2> |
| <p>The handler is available on the <a href="http://felix.apache.org/site/download.html" title="Download">download</a> page.<br> |
| Sources 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>. |
| <br clear="all"> |
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