| <html><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Chapter 5. Migrating to OSGi</title><meta content="DocBook XSL Stylesheets V1.76.0" name="generator"><link rel="home" href="index.html" title="Virgo Programmer Guide"><link rel="up" href="index.html" title="Virgo Programmer Guide"><link rel="prev" href="ch04s10.html" title="Application Versioning"><link rel="next" href="ch05s02.html" title="Migrating to a Plan or a PAR"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="navheader"><table summary="Navigation header" width="100%"><tr><td align="left" width="20%"><a accesskey="p" href="ch04s10.html">Prev</a> </td><th align="center" width="60%"> </th><td align="right" width="20%"> <a accesskey="n" href="ch05s02.html">Next</a></td></tr></table><hr></div><div class="chapter" title="Chapter 5. Migrating to OSGi"><div class="titlepage"><div><div><h2 class="title"><a name="migrating-to-osgi"></a>Chapter 5. Migrating to OSGi</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="ch05.html#migrating-to-osgi-web">Migrating Web Applications</a></span></dt><dd><dl><dt><span class="section"><a href="ch05.html#migrating-to-osgi-web-standard-war">Standard WAR</a></span></dt><dt><span class="section"><a href="ch05.html#migrating-to-osgi-web-shared-libraries-war">Shared Libraries WAR</a></span></dt><dt><span class="section"><a href="ch05.html#migrating-to-osgi-web-shared-services-war">Shared Services WAR</a></span></dt><dt><span class="section"><a href="ch05.html#migrating-to-osgi-web-summary">Web Migration Summary</a></span></dt></dl></dd><dt><span class="section"><a href="ch05s02.html">Migrating to a Plan or a PAR</a></span></dt><dd><dl><dt><span class="section"><a href="ch05s02.html#migrating-to-osgi-parplan-bundles">Creating the Application Bundles</a></span></dt><dt><span class="section"><a href="ch05s02.html#migrating-to-osgi-parplan-decide">Plan or PAR?</a></span></dt></dl></dd></dl></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 Server for Apache Tomcat | |
| will find that their applications typically fall into one of the following | |
| categories. | |
| </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><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 class="listitem"><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 Server for Apache Tomcat. See <a class="xref" href="ch05s02.html" title="Migrating to a Plan or a PAR">Migrating to a Plan or a PAR</a> for details. | |
| </p></li></ul></div><p> | |
| </p><div class="section" title="Migrating Web Applications"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="migrating-to-osgi-web"></a>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 Server for Apache Tomcat | |
| 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" title="Standard WAR"><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 Server for Apache Tomcat, | |
| 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 Server for Apache Tomcat User Guide</a> | |
| is pretty much all that you need to do to get started. Furthermore, you will gain | |
| familiarity with the Virgo Server for Apache Tomcat, while preparing to take advantage of the other formats. | |
| </p></div><div class="section" title="Shared Libraries WAR"><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" title="Shared Services WAR"><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" title="Web Migration Summary"><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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