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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.<BR> |
| A whiteboard is based on two different roles:</P> |
| <UL class="alternate" type="square"> |
| <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 <SPAN class="nobr"><A href="http://www.osgi.org/wiki/uploads/Links/whiteboard.pdf" title="Visit page outside Confluence" rel="nofollow">document<SUP><IMG class="rendericon" src="../../cwiki.apache.org/confluence/images/icons/linkext7.gif" height="7" width="7" align="absmiddle" alt="" border="0"></SUP></A></SPAN><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="codeContent"> |
| <PRE class="code-xml"><SPAN class="code-tag"><ipojo <SPAN class="code-keyword">xmlns:wbp</SPAN>=<SPAN class="code-quote">"org.apache.felix.ipojo.white-board-pattern"</SPAN>></SPAN> |
| <component |
| className=<SPAN class="code-quote">"org.apache.felix.ipojo.test.FooWhiteBoardPattern"</SPAN> |
| > |
| <wbp:wbp |
| filter=<SPAN class="code-quote">"(my.property=1)"</SPAN> |
| onArrival=<SPAN class="code-quote">"onArrival"</SPAN> |
| onDeparture=<SPAN class="code-quote">"onDeparture"</SPAN> |
| onModification=<SPAN class="code-quote">"onModification"</SPAN> |
| /> |
| |
| <SPAN class="code-tag"><provides/></SPAN> |
| <SPAN class="code-tag"></component></SPAN></PRE> |
| </DIV></DIV> |
| <P>Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.white-board-patter" 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="codeContent"> |
| <PRE class="code-java"><SPAN class="code-keyword">public</SPAN> class FooWhiteBoardPattern <SPAN class="code-keyword">implements</SPAN> Observable { |
| List list = <SPAN class="code-keyword">new</SPAN> ArrayList(); |
| <SPAN class="code-object">int</SPAN> modifications = 0; |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">synchronized</SPAN> void onArrival(ServiceReference ref) { |
| list.add(ref); |
| } |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">synchronized</SPAN> void onDeparture(ServiceReference ref) { |
| list.remove(ref); |
| } |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">synchronized</SPAN> void onModification(ServiceReference ref) { |
| modifications = modifications + 1; |
| } |
| <SPAN class="code-keyword">public</SPAN> <SPAN class="code-keyword">synchronized</SPAN> Map getObservations() { |
| Map map = <SPAN class="code-keyword">new</SPAN> HashMap(); |
| map.put(<SPAN class="code-quote">"list"</SPAN>, list); |
| map.put(<SPAN class="code-quote">"modifications"</SPAN>, <SPAN class="code-keyword">new</SPAN> <SPAN class="code-object">Integer</SPAN>(modifications)); |
| <SPAN class="code-keyword">return</SPAN> map; |
| }</PRE> |
| </DIV></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> |
| <TABLE cellpadding="5" width="85%" cellspacing="8px" class="noteMacro" border="0" align="center"><COLGROUP><COL width="24"><COL></COLGROUP><TR><TD valign="top"><IMG src="../../cwiki.apache.org/confluence/images/icons/emoticons/warning.gif" width="16" height="16" align="absmiddle" alt="" border="0"></TD><TD> |
| <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></TABLE> |
| <H2><A name="WhiteBoardPatternHandler-Download"></A>Download</H2> |
| <P>The handler is available on the <A href="download.html" title="Download">download</A> page.<BR> |
| Sources are available on the Felix trunk at the following location: <SPAN class="nobr"><A href="http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/whiteboard" title="Visit page outside Confluence" rel="nofollow">http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/whiteboard<SUP><IMG class="rendericon" src="../../cwiki.apache.org/confluence/images/icons/linkext7.gif" height="7" width="7" align="absmiddle" alt="" border="0"></SUP></A></SPAN></P></TD> |
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| <H6><A name="WhiteBoardPatternHandler-Overview"></A><B>Overview</B></H6> |
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| <H6><A name="WhiteBoardPatternHandler-GettingStarted"></A><B>Getting Started</B></H6> |
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| <H6><A name="WhiteBoardPatternHandler-UserGuide"></A><B>User Guide</B></H6> |
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| <H6><A name="WhiteBoardPatternHandler-Tools"></A><B>Tools</B></H6> |
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| |
| |
| <H6><A name="WhiteBoardPatternHandler-DeveloperGuide"></A><B>Developer Guide</B></H6> |
| <UL> |
| <LI>API: <SPAN class="nobr"><A href="http://people.apache.org/~clement/ipojo/api/0.8/" title="Visit page outside Confluence" rel="nofollow">0.8<SUP><IMG class="rendericon" src="../../cwiki.apache.org/confluence/images/icons/linkext7.gif" height="7" width="7" align="absmiddle" alt="" border="0"></SUP></A></SPAN></LI> |
| <LI><A href="how-to-write-your-own-handler.html" title="How to write your own handler">How to write your own handler</A></LI> |
| <LI><A href="how-to-use-ipojo-manipulation-metadata.html" title="How to use iPOJO Manipulation Metadata">How to use iPOJO Manipulation Metadata</A></LI> |
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| <H6><A name="WhiteBoardPatternHandler-Misc%26Contact"></A><B>Misc & Contact</B></H6> |
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