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| <H1><A name="ExtenderPatternHandler-Theextenderpatternhandler"></A>The extender pattern handler</H1> |
| <P>The objective of this handler is to simplify the development of extender-based architecture. This architecture-style is based on two different roles:</P> |
| <UL> |
| <LI>The extender</LI> |
| <LI>The extension</LI> |
| </UL> |
| |
| |
| <P><IMG src="extender-pattern-handler.data/extender.png" align="absmiddle" border="0"><BR> |
| The relation is basically a 1..n relation. The extender tracks extensions. The particularity of this architecture-style is that extensions are packaged in different bundles. An extension is detected by analyzing the bundle. Indeed these bundles can have a special mark in their manifest of a special file...<BR> |
| Implementing an extender pattern could be complex as the extender needs to track these marks dynamically. When a bundle starts, it needs to look at the mark. Then a bundle leave, the extender must release all object created from this bundle.<BR> |
| This handler tracks bundle for you based on the specified required mark. At each time a matching bundle appears or disappears, a callback is invoked. The mark is currently a header in the bundle manifest.<BR> |
| Nowadays, a lot of frameworks use this pattern such as iPOJO it-self (to find both bundles containing components and bundles adding a new implementation type), Spring-DM ...</P> |
| |
| <H2><A name="ExtenderPatternHandler-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:extender</SPAN>=<SPAN class="code-quote">"org.apache.felix.ipojo.extender"</SPAN>></SPAN> |
| <Component |
| className=<SPAN class="code-quote">"org.apache.felix.ipojo.extender.myextender"</SPAN>> |
| |
| <SPAN class="code-tag"><!—Extender Pattern handler configuration --></SPAN> |
| <extender:extender |
| extension=<SPAN class="code-quote">"My-Extension"</SPAN> |
| onArrival=<SPAN class="code-quote">"onBundleArrival"</SPAN> |
| onDeparture=<SPAN class="code-quote">"onBundleDeparture"</SPAN> |
| /> |
| |
| <SPAN class="code-tag"><callback transition=<SPAN class="code-quote">"invalidate"</SPAN> method=<SPAN class="code-quote">"stopping"</SPAN> /></SPAN> |
| <SPAN class="code-tag"><callback transition=<SPAN class="code-quote">"validate"</SPAN> method=<SPAN class="code-quote">"starting"</SPAN> /></SPAN> |
| <SPAN class="code-tag"><provides /></SPAN> |
| <SPAN class="code-tag"></Component></SPAN> |
| <SPAN class="code-tag"></iPOJO></SPAN></PRE> |
| </DIV></DIV> |
| <P>Notice that, this handler is an external handler. So, it uses the "org.apache.felix.ipojo.extender" namespace.<BR> |
| Once described, you can implement your component. The methods specified methods will be called when a matching bundle arrives or leaves.<BR> |
| In the previous example, these methods could be: </P> |
| <DIV class="code"><DIV class="codeContent"> |
| <PRE class="code-java">void onBundleArrival(Bundle bundle, <SPAN class="code-object">String</SPAN> header) { |
| <SPAN class="code-comment">// Do something |
| </SPAN>} |
| |
| void onBundleDeparture(Bundle bundle) { |
| <SPAN class="code-comment">// Do something |
| </SPAN>}</PRE> |
| </DIV></DIV> |
| <P>Notice the different signatures of the methods. The arrival method is called with the arriving bundle and the matching header value (i.e. the value of the My-Extension header of the bundle manifest). The departure method just receives the leaving bundle.</P> |
| <H2><A name="ExtenderPatternHandler-Configuration"></A>Configuration</H2> |
| <P>The handler has only three mandatory attributes:</P> |
| <UL> |
| <LI>Extension: declaring the looked manifest header.</LI> |
| <LI>onArrival: declaring the method to invoke when a matching bundle arrives</LI> |
| <LI>onDeparture: declaring the method to invoke when a matching bundle leaves</LI> |
| </UL> |
| |
| |
| <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 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="ExtenderPatternHandler-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/extender/" title="Visit page outside Confluence" rel="nofollow">http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/extender/<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> |
| |
| <H2><A name="ExtenderPatternHandler-Amorerealisticexample"></A>A more realistic example</H2> |
| <P>The Junit4OSGi framework, available <SPAN class="nobr"><A href="https://svn.apache.org/repos/asf/felix/trunk/ipojo/examples/junit4osgi" title="Visit page outside Confluence" rel="nofollow">here<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> , uses this handler to track Junit Test Suite offered by the installed bundles. The Junit4Osgi bundle has a component using this handler to be notified when a bundle with the "Test-Suite" header appears or leaves.</P> |
| </TD> |
| <TD class="confluenceTd" valign="top" width="20%"> |
| <H6><A name="ExtenderPatternHandler-Overview"></A><B>Overview</B></H6> |
| <UL> |
| <LI><A href="apache-felix-ipojo.html" title="Apache Felix iPOJO">Home Page</A></LI> |
| <LI><A href="apache-felix-ipojo-feature-overview.html" title="Apache Felix iPOJO Feature Overview">iPOJO Feature Overview</A></LI> |
| <LI><A href="download.html" title="Download">Download & Install </A></LI> |
| </UL> |
| |
| |
| <H6><A name="ExtenderPatternHandler-GettingStarted"></A><B>Getting Started</B></H6> |
| <UL> |
| <LI><A href="ipojo-in-10-minutes.html" title="iPOJO in 10 minutes">iPOJO in 10 minutes</A></LI> |
| <LI><A href="ipojo-hello-word-maven-based-tutorial.html" title="iPOJO Hello Word (Maven-Based) tutorial">iPOJO Hello Word (Maven-Based) tutorial</A></LI> |
| <LI><A href="ipojo-advanced-tutorial.html" title="iPOJO Advanced Tutorial">iPOJO Advanced Tutorial</A></LI> |
| </UL> |
| |
| |
| <H6><A name="ExtenderPatternHandler-UserGuide"></A><B>User Guide</B></H6> |
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| <LI><A href="describing-components.html" title="Describing components">Describing components (handler list) </A></LI> |
| <LI><A href="how-to-use-ipojo-annotations.html" title="How to use iPOJO Annotations">How to use iPOJO Annotations</A></LI> |
| <LI><A href="using-xml-schemas.html" title="Using XML Schemas">Using XML Schemas</A></LI> |
| <LI><A href="ipojo-advanced-topics.html" title="iPOJO Advanced Topics">Advanced Topics</A></LI> |
| <LI><A href="ipojo-faq.html" title="iPOJO FAQ">FAQ</A></LI> |
| </UL> |
| |
| |
| <H6><A name="ExtenderPatternHandler-Tools"></A><B>Tools</B></H6> |
| <UL> |
| <LI><A href="ipojo-eclipse-plug-in.html" title="iPOJO Eclipse Plug-in">iPOJO Eclipse Plug-in</A></LI> |
| <LI><A href="ipojo-ant-task.html" title="iPOJO Ant Task">iPOJO Ant Task</A></LI> |
| <LI><A href="ipojo-maven-plug-in.html" title="iPOJO Maven Plug-in">iPOJO Maven Plug-in</A></LI> |
| <LI><A href="ipojo-concepts-overview.html" title="iPOJO Concepts Overview">iPOJO concepts overview</A></LI> |
| </UL> |
| |
| |
| <H6><A name="ExtenderPatternHandler-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> |
| </UL> |
| |
| |
| <H6><A name="ExtenderPatternHandler-Misc%26Contact"></A><B>Misc & Contact</B></H6> |
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| <LI><A href="apache-felix-ipojo-issuestracker.html" title="apache-felix-ipojo-issuestracker">Issues Tracker</A></LI> |
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| <LI><A href="apache-felix-ipojo-supportedosgi.html" title="apache-felix-ipojo-supportedOSGi">Supported OSGi Implementations</A></LI> |
| <LI><A href="future-ideas.html" title="Future Ideas">Future Ideas</A></LI> |
| <LI><A href="contact.html" title="Contact">Contact</A></LI> |
| <LI><A href="related-works.html" title="Related Works">Related Works</A></LI> |
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