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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">3.2 Middle Tier Highlights</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch03.html">Prev</a> </td><th width="60%" align="center">3. GreenPages Highlights</th><td width="20%" align="right"> <a accesskey="n" href="ch03s03.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="highlights.middletier"></a>3.2 Middle Tier Highlights</h2></div></div></div><p> |
| In the middle tier of GreenPages, the DataSource bundle <code class="literal">greenpages.db</code> constructs a DataSource and |
| publishes it in the service registry and the JPA bundle <code class="literal">greenpages.jpa</code> uses the datasource to define a JPA entity manager |
| which provides an object-relational mapping between directory listings and the database. |
| The JPA bundle also uses declarative transaction management to ensure its persistence operations are performed inside transactions. |
| </p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e959"></a>DataSource</h3></div></div></div><p> |
| The file <code class="filename">src/main/resources/META-INF/spring/module-context.xml</code> in the <code class="literal">greenpages.db</code> project |
| declares the Spring <span class="emphasis"><em>p-namespace</em></span>: |
| </p><pre class="programlisting"><<span class="hl-tag">beans</span> <span class="hl-attribute">xmlns</span>=<span class="hl-value">"http://www.springframework.org/schema/beans"</span> |
| <span class="hl-attribute">xmlns:xsi</span>=<span class="hl-value">"http://www.w3.org/2001/XMLSchema-instance"</span> |
| <span class="hl-attribute">xsi:schemaLocation</span>=<span class="hl-value">"http://www.springframework.org/schema/beans |
| http://www.springframework.org/schema/beans/spring-beans.xsd"</span> |
| <span class="hl-attribute">xmlns:p</span>=<span class="hl-value">"http://www.springframework.org/schema/p"</span>> |
| </pre><p> |
| which is then used to define properties of a datasource bean: |
| </p><pre class="programlisting"><<span class="hl-tag">bean</span> <span class="hl-attribute">id</span>=<span class="hl-value">"dataSource"</span> <span class="hl-attribute">class</span>=<span class="hl-value">"org.apache.commons.dbcp.BasicDataSource"</span> |
| <span class="hl-attribute">p:driverClassName</span>=<span class="hl-value">"org.h2.Driver"</span> <span class="hl-attribute">p:url</span>=<span class="hl-value">"jdbc:h2:~/greenpages-db/greenpages"</span> |
| <span class="hl-attribute">p:username</span>=<span class="hl-value">"greenpages"</span> <span class="hl-attribute">p:password</span>=<span class="hl-value">"pass"</span> |
| <span class="hl-attribute">init-method</span>=<span class="hl-value">"createDataSource"</span> <span class="hl-attribute">destroy-method</span>=<span class="hl-value">"close"</span>/> |
| </pre><p> |
| </p><p> |
| The file <code class="filename">src/main/resources/META-INF/spring/osgi-context.xml</code> publishes the datasource bean as a service in the |
| service registry using Spring DM: |
| </p><pre class="programlisting"><<span class="hl-tag">osgi:service</span> <span class="hl-attribute">ref</span>=<span class="hl-value">"dataSource"</span> <span class="hl-attribute">interface</span>=<span class="hl-value">"javax.sql.DataSource"</span>/> |
| </pre><p> |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e987"></a>EntityManager</h3></div></div></div><p> |
| The <code class="classname">greenpages.jpa.JpaDirectory</code> class in the folder <code class="filename">src/main/java</code> of the |
| <code class="literal">greenpages.jpa</code> project uses the <code class="literal">@Repository</code> annotation to make it eligible for Spring DataAccessException translation |
| (which abstracts implementation-specific persistence exceptions to protect the application from details of the persistence implementation): |
| </p><pre class="programlisting">@Repository |
| <span class="hl-keyword">final</span> <span class="hl-keyword">class</span> JpaDirectory <span class="hl-keyword">implements</span> Directory { |
| </pre><p> |
| and also declares an entity manager which will be injected by Spring: |
| </p><pre class="programlisting">@PersistenceContext |
| <span class="hl-keyword">private</span> EntityManager em; |
| </pre><p> |
| </p><p> |
| The file <code class="filename">src/main/resources/META-INF/spring/module-context.xml</code> in the <code class="literal">greenpages.jpa</code> project |
| declares an entity manager factory based on EclipseLink JPA: |
| </p><pre class="programlisting"><<span class="hl-tag">bean</span> <span class="hl-attribute">id</span>=<span class="hl-value">"entityManagerFactory"</span> |
| <span class="hl-attribute">class</span>=<span class="hl-value">"org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean"</span> |
| <span class="hl-attribute">p:dataSource-ref</span>=<span class="hl-value">"dataSource"</span>> |
| <<span class="hl-tag">property</span> <span class="hl-attribute">name</span>=<span class="hl-value">"jpaVendorAdapter"</span>> |
| <<span class="hl-tag">bean</span> <span class="hl-attribute">id</span>=<span class="hl-value">"jpaVendorAdapter"</span> |
| <span class="hl-attribute">class</span>=<span class="hl-value">"org.springframework.orm.jpa.vendor.EclipseLinkJpaVendorAdapter"</span> |
| <span class="hl-attribute">p:databasePlatform</span>=<span class="hl-value">"org.eclipse.persistence.platform.database.HSQLPlatform"</span> |
| <span class="hl-attribute">p:showSql</span>=<span class="hl-value">"true"</span>/> |
| <<span class="hl-tag">/property</span>> |
| <<span class="hl-tag">/bean</span>> |
| </pre><p> |
| </p><p> |
| The same file enables scanning for annotations, including <code class="literal">@PersistenceContext</code>: |
| </p><pre class="programlisting"><<span class="hl-tag">context:annotation-config</span>/> |
| </pre><p> |
| enables load-time weaving, which is needed by the entity manager factory: |
| </p><pre class="programlisting"><<span class="hl-tag">context:load-time-weaver</span> <span class="hl-attribute">aspectj-weaving</span>=<span class="hl-value">"on"</span>/> |
| </pre><p> |
| and specifies a bean post processor to perform exception translation for <code class="literal">@Repository</code> classes: |
| </p><pre class="programlisting"><<span class="hl-tag">bean</span> <span class="hl-attribute">class</span>=<span class="hl-value">"org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"</span>/> |
| </pre><p> |
| </p><p> |
| The file <code class="filename">src/main/resources/META-INF/persistence.xml</code> defines a persistence unit for a <code class="classname">JpaListing</code> |
| directory listing class. |
| </p><pre class="programlisting"><<span class="hl-tag">persistence</span> <span class="hl-attribute">xmlns</span>=<span class="hl-value">"http://java.sun.com/xml/ns/persistence"</span> |
| <span class="hl-attribute">xmlns:xsi</span>=<span class="hl-value">"http://www.w3.org/2001/XMLSchema-instance"</span> |
| <span class="hl-attribute">xsi:schemaLocation</span>=<span class="hl-value">"http://java.sun.com/xml/ns/persistence |
| http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"</span> |
| <span class="hl-attribute">version</span>=<span class="hl-value">"1.0"</span>> |
| |
| <<span class="hl-tag">persistence-unit</span> <span class="hl-attribute">name</span>=<span class="hl-value">"GreenPages"</span> <span class="hl-attribute">transaction-type</span>=<span class="hl-value">"RESOURCE_LOCAL"</span>> |
| <<span class="hl-tag">class</span>>greenpages.jpa.JpaListing<<span class="hl-tag">/class</span>> |
| <<span class="hl-tag">/persistence-unit</span>> |
| |
| <<span class="hl-tag">/persistence</span>> |
| </pre><p> |
| </p><p> |
| The file <code class="filename">src/main/resources/META-INF/orm.xml</code> defines an entity mapping for the <code class="classname">JpaListing</code> class. |
| </p><pre class="programlisting"><<span class="hl-tag">entity-mappings</span> <span class="hl-attribute">xmlns</span>=<span class="hl-value">"http://java.sun.com/xml/ns/persistence/orm"</span> |
| <span class="hl-attribute">xmlns:xsi</span>=<span class="hl-value">"http://www.w3.org/2001/XMLSchema-instance"</span> |
| <span class="hl-attribute">xsi:schemaLocation</span>=<span class="hl-value">"http://java.sun.com/xml/ns/persistence/orm |
| http://java.sun.com/xml/ns/persistence/orm_1_0.xsd"</span> |
| <span class="hl-attribute">version</span>=<span class="hl-value">"1.0"</span>> |
| <<span class="hl-tag">package</span>>greenpages.jpa<<span class="hl-tag">/package</span>> |
| <<span class="hl-tag">entity</span> <span class="hl-attribute">class</span>=<span class="hl-value">"greenpages.jpa.JpaListing"</span> <span class="hl-attribute">name</span>=<span class="hl-value">"Listing"</span>> |
| <<span class="hl-tag">table</span> <span class="hl-attribute">name</span>=<span class="hl-value">"LISTING"</span>/> |
| <<span class="hl-tag">attributes</span>> |
| <<span class="hl-tag">id</span> <span class="hl-attribute">name</span>=<span class="hl-value">"listingNumber"</span>> |
| <<span class="hl-tag">column</span> <span class="hl-attribute">name</span>=<span class="hl-value">"LISTING_NUMBER"</span>/> |
| <<span class="hl-tag">generated-value</span> <span class="hl-attribute">strategy</span>=<span class="hl-value">"TABLE"</span>/> |
| <<span class="hl-tag">/id</span>> |
| <<span class="hl-tag">basic</span> <span class="hl-attribute">name</span>=<span class="hl-value">"firstName"</span>> |
| <<span class="hl-tag">column</span> <span class="hl-attribute">name</span>=<span class="hl-value">"FIRST_NAME"</span>/> |
| <<span class="hl-tag">/basic</span>> |
| … |
| <<span class="hl-tag">/attributes</span>> |
| <<span class="hl-tag">/entity</span>> |
| <<span class="hl-tag">/entity-mappings</span>> |
| </pre><p> |
| </p></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="d0e1060"></a>Transaction Management</h3></div></div></div><p> |
| The <code class="classname">greenpages.jpa.JpaDirectory</code> class in the folder <code class="filename">src/main/java</code> of the |
| <code class="literal">greenpages.jpa</code> project uses the <code class="literal">@Transactional</code> annotation to provide transaction demarcation |
| (beginning and committing a transaction around each method in this case): |
| </p><pre class="programlisting">@Transactional |
| … |
| <span class="hl-keyword">final</span> <span class="hl-keyword">class</span> JpaDirectory <span class="hl-keyword">implements</span> Directory { |
| </pre><p> |
| </p><p> |
| The file <code class="filename">src/main/resources/META-INF/spring/module-context.xml</code> enables AspectJ weaving for transaction demarcation: |
| </p><pre class="programlisting"><<span class="hl-tag">tx:annotation-driven</span> <span class="hl-attribute">mode</span>=<span class="hl-value">"aspectj"</span>/> |
| </pre><p> |
| and specifies that the Spring <code class="classname">JpaTransactionManager</code> should be used and associated with the entity manager factory: |
| </p><pre class="programlisting"><<span class="hl-tag">bean</span> <span class="hl-attribute">id</span>=<span class="hl-value">"transactionManager"</span> <span class="hl-attribute">class</span>=<span class="hl-value">"org.springframework.orm.jpa.JpaTransactionManager"</span> |
| <span class="hl-attribute">p:entityManagerFactory-ref</span>=<span class="hl-value">"entityManagerFactory"</span>/> |
| </pre><p> |
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