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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">3.4 A Guide to Forming Bundles</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch03s03.html">Prev</a> </td><th width="60%" align="center">3. Deployment Architecture</th><td width="20%" align="right"> <a accesskey="n" href="ch04.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="architecture-forming-bundles"></a>3.4 A Guide to Forming Bundles</h2></div></div></div><p> | |
| So what makes an application suitable for deployment on the Virgo Server for Apache Tomcat? Since | |
| OSGi is at the heart of the VTS, modular applications consisting of | |
| bundles, which each represent distinct functionality and well-defined boundaries, can | |
| take maximum advantage of the OSGi container’s capabilities. The core ideas behind | |
| forming bundles require following good software engineering practices: separation of | |
| concerns, loose coupling, and communication through clear interfaces. In this section, | |
| we look at a few approaches that you may use to create modular applications for | |
| Virgo Server for Apache Tomcat deployment. Please consider the following discussion as guidelines and | |
| not as rules. | |
| </p><p> | |
| Bundles can be formed along horizontal slices of layering and vertical slices of | |
| function. The objective is to enable independent development of each bundle and minimize | |
| the skills required to develop each bundle. | |
| </p><p> For example, an application could have the following bundles: | |
| <span class="emphasis"><em>infrastructure</em></span>, <span class="emphasis"><em>domain</em></span>, | |
| <span class="emphasis"><em>repository</em></span>, <span class="emphasis"><em>service</em></span>, and | |
| <span class="emphasis"><em>web</em></span> as shown in the following diagram.</p><div class="mediaobject"><img src="images/bundle-dependencies-layers.png"></div><p> Each bundle consists of types appropriate for that layer and exports | |
| packages and services to be used by other layers. Let’s examine each bundle in | |
| more detail: </p><div class="table"><a name="architecture-forming-bundles-across-layers-table"></a><p class="title"><b>Table 3.2. Bundles across layers</b></p><div class="table-contents"><table summary="Bundles across layers" style="border-collapse: collapse;border-top: 1.0pt solid ; border-bottom: 1.0pt solid ; border-left: 1.0pt solid ; border-right: 1.0pt solid ; "><colgroup><col><col><col><col><col></colgroup><thead><tr><th style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Bundles</th><th style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Imported Packages</th><th style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Exported Packages</th><th style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Consumed Services</th><th style="border-bottom: 1.0pt solid ; ">Published Services</th></tr></thead><tbody><tr><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Infrastructure</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Third-party libraries</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Infrastructure interfaces</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">None</td><td style="border-bottom: 1.0pt solid ; ">None</td></tr><tr><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Domain</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Depends: for example, if JPA is used to annotate persistent | |
| types, then JPA packages.</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Public domain types</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">None</td><td style="border-bottom: 1.0pt solid ; ">None</td></tr><tr><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Web</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Domain, Service</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">None</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Service beans</td><td style="border-bottom: 1.0pt solid ; ">None</td></tr><tr><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Service</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Domain, Infrastructure, Repository</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Service interfaces</td><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Repository beans</td><td style="border-bottom: 1.0pt solid ; ">Service beans</td></tr><tr><td style="border-right: 1.0pt solid ; ">Repository</td><td style="border-right: 1.0pt solid ; ">Domain, Third-party libraries, ORM bundles, etc.</td><td style="border-right: 1.0pt solid ; ">Repository interfaces</td><td style="border-right: 1.0pt solid ; ">DataSources, ORM session/entity managers, etc.</td><td style="">Repository beans</td></tr></tbody></table></div></div><p><br class="table-break"></p><p> Within each layer, you may create bundles for each subsystem representing a vertical | |
| slice of business functionality. For example, as shown in the following figure, the | |
| service layer is divided into two bundles each representing separate business | |
| functions. </p><div class="mediaobject"><img src="images/bundle-dependencies-verticals.png"></div><p> You can similarly separate the repositories, domain classes, and web controllers | |
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