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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. The Middle Tier</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s07.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="middle-tier"></a>5. The Middle Tier</h2></div></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="middle-tier.introduction"></a>5.1 Introduction</h2></div></div></div><p> | |
| GreenPages’ middle-tier provides implementations of the <code class="literal">Directory</code> and <code class="literal">Listing</code> | |
| interfaces that can be used by the Web bundle. | |
| The implementation will use EclipseLink JPA to access a database via a <code class="literal">DataSource</code> published in the | |
| OSGi service registry. | |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="middle-tier.introduction.database"></a>The database</h3></div></div></div><p> | |
| The GreenPages application uses a very simple database that contains a single table. | |
| The table, named <code class="literal">LISTING</code>, consists of four columns: | |
| </p><div class="informaltable"><table 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></colgroup><tbody><tr><td style="border-right: 1.0pt solid ; "><code class="literal">LISTING_NUMBER</code></td><td style="border-right: 1.0pt solid ; "><code class="literal">FIRST_NAME</code></td><td style="border-right: 1.0pt solid ; "><code class="literal">LAST_NAME</code></td><td style=""><code class="literal">EMAIL_ADDRESS</code></td></tr></tbody></table></div><p> | |
| Scripts are provided with the sample source code (in <code class="literal">$GREENPAGES_HOME/db</code>) to start, create, and populate the database. | |
| These will be used during the creation of the middle tier. | |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="middle-tier.introduction.jpa"></a>Using JPA</h3></div></div></div><p> | |
| The middle tier will provide JPA-based implementations of the <code class="literal">Directory</code> and <code class="literal">Listing</code> interfaces with the four | |
| attributes of a <code class="literal">Listing</code> (first name, last name, email address, and id) being mapped to the corresponding columns in the | |
| <code class="literal">LISTING</code>. | |
| JPA will be used to implement the queries that search the database and return <code class="literal">Listings</code>. | |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="middle-tier.introduction.structure"></a>Structure</h3></div></div></div><p> | |
| The middle tier consists of two bundles, <code class="literal">greenpages.jpa</code> that publishes a <code class="literal">Directory</code> | |
| implementation for consumption by the Web bundle, and <code class="literal">greenpages.db</code> to configure and publish the | |
| <code class="literal">DataSource</code> used to access the database. | |
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