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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">6.5 Form Tags PAR</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch06s04.html">Prev</a> </td><th width="60%" align="center">6. Case Study: Migrating the Form Tags Sample Application</th><td width="20%" align="right"> <a accesskey="n" href="ch06s06.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="formtags-case-study-par"></a>6.5 Form Tags PAR</h2></div></div></div><p> |
| The final step in the migration is that of a full blown |
| OSGi |
| application with web support. The Virgo Server for Apache Tomcat introduces a |
| new packaging and deployment format: the PAR. |
| |
| A PAR is a standard JAR |
| with a " |
| <code class="literal">.par</code> |
| " |
| file extension which contains all of the modules of your |
| application (e.g., service, domain, and infrastructure bundles |
| as well |
| as a WAR for web applications) in a single deployment unit. |
| Moreover, |
| a PAR defines both a physical and logical application boundary. |
| </p><p> |
| The PAR sample is comprised of four directories, as shown below. |
| </p><p> |
| <img src="images/formtags-case-study-par-sample.png"> |
| </p><p> |
| The |
| <code class="literal">formtags-par</code> |
| directory is a build project that |
| understands how to create the PAR |
| from its constituent bundles. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="formtags-case-study-par-granularity"></a>Granularity of the PAR</h3></div></div></div><p> |
| Achieving the appropriate level of granularity for your OSGi |
| application is more of an art than a science. It helps to look |
| at the |
| different requirements: |
| </p><div class="table"><a name="formtags-case-study-par-granularity-drivers-table"></a><p class="title"><b>Table 6.1. Granularity drivers</b></p><div class="table-contents"><table summary="Granularity drivers" 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></colgroup><thead><tr><th style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Requirement</th><th style="border-bottom: 1.0pt solid ; ">Description</th></tr></thead><tbody><tr><td style="border-right: 1.0pt solid ; border-bottom: 1.0pt solid ; ">Domain/Technical Layering</td><td style="border-bottom: 1.0pt solid ; "> |
| Applications can be split either by domain (i.e., |
| by use case or |
| <span class="emphasis"><em>vertically</em></span> |
| ) or |
| by their technical layers (i.e., |
| <span class="emphasis"><em>horizontally</em></span> |
| ). |
| Since the Form Tags application essentially has only |
| a single |
| use case, the bundles are split by technical layering |
| (i.e., |
| domain, service, and web). |
| </td></tr><tr><td style="border-right: 1.0pt solid ; ">Refreshability</td><td style=""> |
| A major benefit of OSGi is that of refreshability: if one |
| bundle |
| is changed, only bundles that have a dependency upon |
| the |
| exported types need to be refreshed. This has a high impact |
| on |
| development time costs as well as production |
| costs. However, |
| this can lead to lots of smaller, fine grained |
| bundles. An |
| example of this granularity would be to |
| separate out the service |
| API and implementation into two different |
| bundles. This means |
| that a change in the implementation |
| wouldn’t require any |
| other bundles to be refreshed. |
| </td></tr></tbody></table></div></div><p><br class="table-break"> |
| Ultimately the right level of granularity will depend upon your |
| particular application and team. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="formtags-case-study-par-domain-and-service"></a>Domain and Service Bundles</h3></div></div></div><p> |
| The service bundle is identical (except for the |
| <code class="literal">Bundle-SymbolicName</code> |
| ) to that |
| in the shared-services variation of the sample. |
| The PAR has |
| also separated out the domain classes into their own bundle. |
| When |
| layering by technical considerations, it is again |
| somewhat of an |
| unofficial convention to have a |
| <code class="literal">.domain</code> |
| bundle. |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="formtags-case-study-par-par"></a>Constructing the PAR</h3></div></div></div><p> |
| Finally we need to construct the PAR itself. |
| The following are |
| the contents of the exploded PAR. |
| </p><p> |
| <img src="images/formtags-case-study-par-exploded.png"> |
| </p><p> |
| You can see that the PAR itself doesn’t contain any |
| resources or |
| Java classes: it simply packages together a related set |
| of bundles |
| as a single, logical unit. |
| </p><p> |
| The PAR does however, contain its own |
| <code class="literal">/META-INF/MANIFEST.MF</code> |
| . |
| </p><pre class="programlisting"> |
| Manifest-Version: 1.0 |
| Application-SymbolicName: org.springframework.showcase.formtags-par |
| Application-Version: 3.0.0 |
| Application-Name: FormTags Showcase Application (PAR) |
| </pre><p> |
| For more information on the contents of the PAR’s |
| <code class="literal">/META-INF/MANIFEST.MF</code> |
| , please consult |
| <a class="xref" href="ch04.html" title="4. Developing Applications">Chapter 4, <i>Developing Applications</i></a> |
| . |
| </p><p> |
| You can now deploy the PAR on the VTS, for |
| example by copying |
| <code class="literal">/dist/formtags-par*.par</code> |
| to the VTS’s |
| <code class="literal">pickup</code> |
| directory. |
| You should then see console output similar to the |
| following: |
| </p><div class="note" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Note"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="images/note.gif"></td><th align="left">Note</th></tr><tr><td align="left" valign="top"><p>The console output has been reformatted to fit this document. |
| </p></td></tr></table></div><pre class="programlisting"> |
| [2009-07-01 15:13:43.306] fs-watcher |
| <SPDE0048I> Processing 'CREATED' event for file 'formtags-par-2.0.0.RELEASE.par'. |
| [2009-07-01 15:13:44.060] fs-watcher |
| <SPDE0010I> Deployment of 'formtags-par' version '2.0.0.RELEASE' completed. |
| [2009-07-01 15:13:44.068] Thread-20 |
| <SPWE0000I> Starting web bundle '/formtags-par'. |
| [2009-07-01 15:13:45.212] Thread-20 |
| <SPWE0001I> Started web bundle '/formtags-par'. |
| </pre><p> |
| Navigate to |
| <a class="ulink" href="http://localhost:8080/formtags-par" target="_top">http://localhost:8080/formtags-par</a> |
| to see the welcome page. |
| </p><div class="tip" style="margin-left: 0.5in; margin-right: 0.5in;"><table border="0" summary="Tip"><tr><td rowspan="2" align="center" valign="top" width="25"><img alt="[Tip]" src="images/tip.gif"></td><th align="left">Tip</th></tr><tr><td align="left" valign="top"> |
| Note that the web application’s context path is explicitly |
| defined via the |
| <code class="literal">Web-ContextPath</code> |
| manifest header in |
| <code class="literal">/META-INF/MANIFEST.MF</code> |
| of the Web application bundle within the PAR. |
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