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| </script><!--End Google Analytics code--></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.3 Spring DM Concepts</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch02s02.html">Prev</a> </td><th width="60%" align="center">2. Concepts</th><td width="20%" align="right"> <a accesskey="n" href="ch02s04.html">Next</a></td></tr></table><hr></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="concepts.springdm"></a>2.3 Spring DM Concepts</h2></div></div></div><p>Spring DM is a project which enables <span class="emphasis"><em>services</em></span> to be published and consumed |
| using descriptions written in XML. |
| Virgo has Spring DM built-in.</p><p>The XML descriptions reside in files with extension <code class="literal">.xml</code> in the |
| bundle’s <code class="literal">META-INF/spring</code> sub-directory.</p><p> |
| To publish a service, an <code class="literal"><osgi:service></code> tag is used, specifying the |
| implementation class of the service and the interface class to be used. |
| Spring DM constructs an instance of the implementation class and |
| publishes that instance in the OSGi service registry under the interface when the bundle is started. |
| </p><p>To consume a service, an <code class="literal"><osgi:reference></code> tag is used and the |
| service may be passed into other Spring beans using Spring’s dependency |
| injection facilities.</p><p>Spring DM automatically creates proxies for OSGi services so that the actual service |
| object may come and go at runtime. |
| If a service disappears, any proxies to the service will wait for the service to re-appear. |
| This effect is known as <span class="emphasis"><em>damping</em></span>.</p><p>When a bundle is started, Spring DM builds the application contexts |
| specified by the XML descriptions, creates proxies for the specified services, and publishes |
| the specified services to the OSGi service registry.</p><p>When a bundle is stopped, Spring DM retracts any services it published on behalf of the bundle |
| and closes the bundle’s application contexts. |
| Virgo turns off damping of a service proxy while the proxy’s application context |
| is being closed.</p><p>(Spring DM has been contributed to Eclipse as the <span class="emphasis"><em>Gemini Blueprint</em></span> project.)</p></div><!--Begin LoopFuse code--><script src="http://loopfuse.net/webrecorder/js/listen.js" type="text/javascript"></script><script type="text/javascript"> |
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