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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">5. Migrating to OSGi</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s09.html">Prev</a> </td><th width="60%" align="center"> </th><td width="20%" align="right"> <a accesskey="n" href="ch05s02.html">Next</a></td></tr></table><hr></div><div class="chapter" lang="en"><div class="titlepage"><div><div><h2 class="title"><a name="migrating-to-osgi"></a>5. Migrating to OSGi</h2></div></div></div><p> | |
| Taking on a new technology such as OSGi may seem a bit daunting at first, | |
| but a proven set of migration steps can help ease the journey. Teams | |
| wishing to migrate existing applications to run on the Virgo Tomcat Server | |
| will find that their applications typically fall into one of the following | |
| categories. | |
| </p><div class="itemizedlist"><ul type="disc"><li><p> | |
| <span class="bold"><strong>Web Application</strong></span>: for web applications, | |
| this chapter provides an overview of the steps required to migrate | |
| from a Standard WAR to a Shared Services WAR. Furthermore, the following | |
| chapter provides a detailed case study involving the migration | |
| of the Spring 3.0 Form Tags show case application. | |
| </p></li><li><p> | |
| <span class="bold"><strong>Anything else</strong></span>: for any other type | |
| of application, you will typically either deploy your application | |
| as multiple individual bundles, as a single PAR file, or as a plan, | |
| which is the recommended approach for deploying applications on | |
| the Virgo Tomcat Server. See <a class="xref" href="ch05s02.html" title="5.2 Migrating to a Plan or a PAR">Section 5.2, “Migrating to a Plan or a PAR”</a> for details. | |
| </p></li></ul></div><p> | |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="migrating-to-osgi-web"></a>5.1 Migrating Web Applications</h2></div></div></div><p> | |
| Many applications may start with the standard WAR format for web applications and | |
| gradually migrate to a more OSGi-oriented architecture. Since the Virgo Tomcat Server | |
| offers several benefits to all supported deployment formats, it provides a smooth | |
| migration path. Of course, depending on your application’s complexity and your | |
| experience with OSGi, you may choose to start immediately with an OSGi-based | |
| architecture. | |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="migrating-to-osgi-web-standard-war"></a>Standard WAR</h3></div></div></div><p> | |
| If you are not yet familiar with OSGi or simply want to deploy an existing web application on the Virgo Tomcat Server, | |
| you can deploy a standard WAR and leverage the VTS with a minimal learning curve. In fact reading the | |
| <a class="ulink" href="../../virgo-user-guide/html/index.html" target="_top">Virgo Tomcat Server User Guide</a> | |
| is pretty much all that you need to do to get started. Furthermore, you will gain | |
| familiarity with the Virgo Tomcat Server, while preparing to take advantage of the other formats. | |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="migrating-to-osgi-web-shared-libraries-war"></a>Shared Libraries WAR</h3></div></div></div><p> | |
| The <span class="emphasis"><em>Shared Libraries WAR</em></span> | |
| format is the first step to reaping the benefits of OSGi. In this phase, you dip your toes into OSGi-based dependency | |
| management by removing JAR files from the WAR and declaring dependencies on corresponding OSGi bundles. | |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="migrating-to-osgi-web-shared-services-war"></a>Shared Services WAR</h3></div></div></div><p> In this phase, you take the next step toward a fully OSGi-based architecture by separating your web artifacts | |
| (e.g., Servlets, Controllers, etc.) from the services they depend on.</p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="migrating-to-osgi-web-summary"></a>Web Migration Summary</h3></div></div></div><p> | |
| The following diagram graphically depicts the migration path from a Standard WAR to a Shared Services WAR. | |
| As you can see, the libraries (<span class="emphasis"><em>libs</em></span>) move from within the deployment artifact | |
| to the Bundle Repository. | |
| Similarly, the services move from within the WAR to external bundles and are accessed via the | |
| OSGi Service Registry. In addition, the overall footprint of the deployment artifact decreases | |
| as you move towards a Shared Services WAR. | |
| </p><div class="mediaobject"><img src="images/migration-path-war-to-shsrv.png"></div><p> | |
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