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| <h1><a name="ExtenderPatternHandler-Theextenderpatternhandler"></a>The extender pattern handler</h1> |
| <p><em>The objective of this handler is to simplify the development of |
| extender-based architecture. This architecture-style is based on two |
| different roles:</em></p> |
| <ul> |
| <li><em>The extender</em></li> |
| <li><em>The extensions</em></li> |
| </ul> |
| |
| |
| <div class="toc"> |
| <ul> |
| <li><a href="#ExtenderPatternHandler-TheExtenderpattern">The Extender pattern</a></li> |
| <li><a href="#ExtenderPatternHandler-Usingthehandler">Using the handler</a></li> |
| <li><a href="#ExtenderPatternHandler-Configuration">Configuration</a></li> |
| <li><a href="#ExtenderPatternHandler-Download">Download</a></li> |
| <li><a href="#ExtenderPatternHandler-Configuringthehandlerwithannotations">Configuring the handler with annotations</a></li> |
| <li><a href="#ExtenderPatternHandler-Amorerealisticexample">A more realistic example</a></li> |
| </ul></div> |
| |
| <h2><a name="ExtenderPatternHandler-TheExtenderpattern"></a>The Extender pattern</h2> |
| |
| <p>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_files/extender.png" border="0" align="absmiddle"></p> |
| |
| <p>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="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">extender</span><span>=</span><span class="attribute-value">"org.apache.felix.ipojo.extender"</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.extender.myextender"</span><span>> </span></td></tr><tr><td class="line2"> </td></tr><tr><td class="line1"> <span class="comments"><!-- Extender Pattern handler configuration --></span><span> </span></td></tr><tr><td class="line2"> <span class="tag"><</span><span>extender:extender </span></td></tr><tr><td class="line1"> <span class="attribute">extension</span><span>=</span><span class="attribute-value">"My-Extension"</span><span> </span></td></tr><tr><td class="line2"> <span class="attribute">onArrival</span><span>=</span><span class="attribute-value">"onBundleArrival"</span><span> </span></td></tr><tr><td class="line1"> <span class="attribute">onDeparture</span><span>=</span><span class="attribute-value">"onBundleDeparture"</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>callback </span><span class="attribute">transition</span><span>=</span><span class="attribute-value">"invalidate"</span><span> </span><span class="attribute">method</span><span>=</span><span class="attribute-value">"stopping"</span><span> </span><span class="tag">/></span><span> </span></td></tr><tr><td class="line1"> <span class="tag"><</span><span>callback </span><span class="attribute">transition</span><span>=</span><span class="attribute-value">"validate"</span><span> </span><span class="attribute">method</span><span>=</span><span class="attribute-value">"starting"</span><span> </span><span class="tag">/></span><span> </span></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><tr><td class="line2"><span class="tag"></</span><span>iPOJO</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:extender="org.apache.felix.ipojo.extender"> |
| <component |
| classname="org.apache.felix.ipojo.extender.myextender"> |
| |
| <!-- Extender Pattern handler configuration --> |
| <extender:extender |
| extension="My-Extension" |
| onArrival="onBundleArrival" |
| onDeparture="onBundleDeparture" |
| /> |
| |
| <callback transition="invalidate" method="stopping" /> |
| <callback transition="validate" method="starting" /> |
| <provides /> |
| </component> |
| </iPOJO></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.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="dp-highlighter"><table class="dp-c" border="0" cellpadding="0" cellspacing="0"><tbody><tr><td class="line1"><span></span><span class="keyword">void</span><span> onBundleArrival(Bundle bundle, String header) { </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">void</span><span> onBundleDeparture(Bundle bundle) { </span></td></tr><tr><td class="line2"> <span class="comment">// Do something</span><span> </span></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">void onBundleArrival(Bundle bundle, String header) { |
| // Do something |
| } |
| |
| void onBundleDeparture(Bundle bundle) { |
| // Do something |
| }</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 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> |
| |
| |
| |
| |
| <div class="box"> |
| <div class="box-yellow-header"> |
| <div class="box-yellow-title"> |
| <img src="extender-pattern-handler_files/warning.gif"> <b>Called despite being invalid</b> |
| </div> |
| </div> |
| <div class="box-yellow-content"> |
| 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. </div> |
| <div class="box-yellow-footer"></div> |
| </div> |
| |
| |
| <h2><a name="ExtenderPatternHandler-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/extender/" rel="nofollow">http://svn.apache.org/repos/asf/felix/trunk/ipojo/handler/extender/</a></p> |
| |
| <h2><a name="ExtenderPatternHandler-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.Bundle; </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.extender.Extender(extension="foo", onArrival="onArrival", onDeparture="onDeparture")</span><span> </span></td></tr><tr><td class="line2"><span class="keyword">public</span><span> </span><span class="keyword">class</span><span> Extender { </span></td></tr><tr><td class="line1"> </td></tr><tr><td class="line2"> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> onArrival(Bundle bundle, String foo) { </span></td></tr><tr><td class="line1"> <span class="comment">// do something</span><span> </span></td></tr><tr><td class="line2"> } </td></tr><tr><td class="line1"> </td></tr><tr><td class="line2"> <span class="keyword">public</span><span> </span><span class="keyword">void</span><span> onDeparture(Bundle bundle) { </span></td></tr><tr><td class="line1"> <span class="comment">// do something</span><span> </span></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.Bundle; |
| |
| @Component |
| @org.apache.felix.ipojo.extender.Extender(extension="foo", onArrival="onArrival", onDeparture="onDeparture") |
| public class Extender { |
| |
| public void onArrival(Bundle bundle, String foo) { |
| // do something |
| } |
| |
| public void onDeparture(Bundle bundle) { |
| // do something |
| } |
| }</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>The <tt>extension</tt> attribute allows setting the bundle filter.</p> |
| |
| |
| <h2><a name="ExtenderPatternHandler-Amorerealisticexample"></a>A more realistic example</h2> |
| <p>The Junit4OSGi framework, available <a href="https://svn.apache.org/repos/asf/felix/trunk/ipojo/examples/junit4osgi" rel="nofollow">here</a> |
| , 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 <tt>Test-Suite</tt> header appears or leaves. |
| <br clear="all"> |
| <br clear="all"></p> |
| |
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