| <html><head><META http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>A Guide to Forming Bundles</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="ch03.html" title="Chapter 3. Deployment Architecture"><link rel="prev" href="ch03s03.html" title="Regions"><link rel="next" href="ch04.html" title="Chapter 4. Developing Applications"></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="ch03s03.html">Prev</a> </td><th align="center" width="60%"> </th><td align="right" width="20%"> <a accesskey="n" href="ch04.html">Next</a></td></tr></table><hr></div><div class="section" title="A Guide to Forming Bundles"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="architecture-forming-bundles"></a>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" border="1"><colgroup><col><col><col><col><col></colgroup><thead><tr><th>Bundles</th><th>Imported Packages</th><th>Exported Packages</th><th>Consumed Services</th><th>Published Services</th></tr></thead><tbody><tr><td>Infrastructure</td><td>Third-party libraries</td><td>Infrastructure interfaces</td><td>None</td><td>None</td></tr><tr><td>Domain</td><td>Depends: for example, if JPA is used to annotate persistent | |
| types, then JPA packages.</td><td>Public domain types</td><td>None</td><td>None</td></tr><tr><td>Web</td><td>Domain, Service</td><td>None</td><td>Service beans</td><td>None</td></tr><tr><td>Service</td><td>Domain, Infrastructure, Repository</td><td>Service interfaces</td><td>Repository beans</td><td>Service beans</td></tr><tr><td>Repository</td><td>Domain, Third-party libraries, ORM bundles, etc.</td><td>Repository interfaces</td><td>DataSources, ORM session/entity managers, etc.</td><td>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 | |
| based on the business role they play.</p></div><div class="navfooter"><hr><table summary="Navigation footer" width="100%"><tr><td align="left" width="40%"><a accesskey="p" href="ch03s03.html">Prev</a> </td><td align="center" width="20%"><a accesskey="u" href="ch03.html">Up</a></td><td align="right" width="40%"> <a accesskey="n" href="ch04.html">Next</a></td></tr><tr><td valign="top" align="left" width="40%"> </td><td align="center" width="20%"><a accesskey="h" href="index.html">Home</a></td><td valign="top" align="right" width="40%"> </td></tr></table></div></body></html> |