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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">4.4 Creating and Using Configuration Artifacts</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="ch04s03.html">Prev</a> </td><th width="60%" align="center">4. Developing Applications</th><td width="20%" align="right"> <a accesskey="n" href="ch04s05.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="developing-applications-configuration-artifacts"></a>4.4 Creating and Using Configuration Artifacts</h2></div></div></div><p> |
| Applications typically include some sort of configuration data |
| that might change depending on the environment in which the |
| application is deployed. For example, if an application connects to a |
| database server using JDBC, the configuration data would include the |
| JDBC URL of the database server, the JDBC drvier, and the username and |
| password that the application uses to connect to the database server. |
| This information often changes as the application is deployed to |
| different computers or the application moves from the testing phase to |
| the production phase. |
| </p><p> |
| Virgo provides a feature called |
| <span class="emphasis"><em>configuration artifacts</em></span> |
| that makes it very easy for you to manage this configuration data. A |
| configuration artifact is simply a properties file that is made |
| available at runtime using the OSGi |
| <code class="literal">ConfigurationAdmin</code> |
| service. When you create this properties file, you set the values of |
| the properties for the specific environment in which you are going to |
| deploy your application, and then update the metadata of your Spring |
| application to use the properties file. You then deploy the |
| application and properties file together, typically as a |
| <a class="link" href="ch04s03.html" title="4.3 Creating Plans">plan</a> |
| . Virgo automatically creates a configuration artifact from |
| the properties file, and you can manage the lifecycle of this |
| configuration artifact in the same way you manage the lifecycle of |
| PARs, bundles, and plans, using the Admin |
| Console. Additionally, Virgo subscribes your |
| application for notification of any refresh of the configuration |
| artifact and the application can then adapt accordingly, which means |
| you can easily |
| <span class="emphasis"><em>change</em></span> |
| the configuration of your application without redeploying it. |
| </p><p>In sum, configuration artifacts, especially when combined with |
| plans, provide an excellent mechanism for managing external |
| configuration data for your applications.</p><p>The following sections describe the format of the configuration |
| artifact, how to update the Spring application context file of your |
| application so that it knows about the configuration artifact, and |
| finally how to include it in a plan alongside your application. </p><p> |
| As an example to illustrate the configuration artifact feature, assume |
| that you have a Spring bean called |
| <code class="literal">PropertiesController</code> |
| whose constructor requires that four property values be passed to it, |
| as shown in the following snippet of Java code: |
| </p><pre class="programlisting">@Controller |
| public class PropertiesController { |
| |
| private final String driverClassName; |
| private final String url; |
| private final String username; |
| private final String password; |
| |
| public PropertiesController(String driverClassName, String url, String username, String password) { |
| this.driverClassName = driverClassName; |
| this.url = url; |
| this.username = username; |
| this.password = password; |
| }</pre><p>In the preceding example, the <code class="literal">PropertiesController</code> constructor requires four property values: <code class="literal">driverClassName</code>, <code class="literal">url</code>, <code class="literal">username</code>, and <code class="literal">password</code>. Note that the example shows just one way that a class might require property values; your application may code it another way.</p><p>Additionally, assume that the following snippet of the associated Spring application context XML file shows how the <code class="literal">PropertiesController</code> bean is configured:</p><pre class="programlisting"><bean class="com.springsource.configuration.properties.PropertiesController"> |
| <constructor-arg value="${driverClassName}"/> |
| <constructor-arg value="${url}"/> |
| <constructor-arg value="${username}"/> |
| <constructor-arg value="${password}"/> |
| </bean></pre><p>The rest of this section describes how the bean can get these property values using a configuration artifact.</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="developing-applications-configuration-artifacts-propfile"></a>Creating the Properties File</h3></div></div></div><p>To create a properties file that in turn will become a configuration artifact when deployed to Virgo from which a Spring bean, such as the <code class="literal">PropertiesController</code> bean, will get the actual property values, follow these guidelines:</p><div class="itemizedlist"><ul type="disc"><li><p>Create a text file in which each property is listed as a name/value pair, one pair per line. Precede comments with a <code class="literal">#</code>. For example:</p><pre class="screen"># Properties for the com.springsource.configuration.properties sample |
| |
| driverClassName = org.w3.Driver |
| url = http://www.springsource.com |
| username = joe |
| password = secret</pre><p>The example shows four properties whose name correspond to the constructor arguments of the <code class="literal">PropertiesController</code> Spring bean.</p></li><li><p>Name the file anything you want, as long as it has a <code class="literal">.properties</code> extension, such as <code class="literal">app-properties.properties</code>.</p></li></ul></div></div><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="developing-applications-configuration-artifacts-app"></a>Updating Your Application</h3></div></div></div><p>To update your application so that it "knows" about the configuration artifact, you update the application's Spring application context XML file, typically located in the <code class="literal">WEB-INF</code> or <code class="literal">META-INF/spring</code> directories (read <a class="link" href="ch04s05.html" title="4.5 Using Spring, Spring DM, and Blueprint">Using Spring and Spring DM</a> |
| to understand which directory to use).</p><p>You use the <code class="literal"><context:property-placeholder></code> element to specify that you want to use the Virgo mechanism for substituting values into bean properties. The <code class="literal">properties-ref</code> attribute of this element points to a <code class="literal"><osgi-compendium:cm-properties></code> element which you use to specify the configuration artifact that contains the property values. You set the value of the <code class="literal">persistent-id</code> attribute of this element equal to the name of the configuration artifact, which is the name of the properties file <span class="emphasis"><em>minus</em></span> the <code class="literal">.properties</code> extension. </p><p>The following sample Spring application context XMl file shows everything wired together; only relevant parts of the file are shown:</p><pre class="programlisting"><?xml version="1.0" encoding="UTF-8"?> |
| <beans xmlns="http://www.springframework.org/schema/beans" |
| xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" |
| xmlns:context="http://www.springframework.org/schema/context" |
| xmlns:osgi-compendium="http://www.springframework.org/schema/osgi-compendium" |
| xsi:schemaLocation="http://www.springframework.org/schema/osgi |
| http://www.springframework.org/schema/osgi/spring-osgi-1.2.xsd |
| http://www.springframework.org/schema/beans |
| http://www.springframework.org/schema/beans/spring-beans-2.5.xsd |
| http://www.springframework.org/schema/context |
| http://www.springframework.org/schema/context/spring-context-2.5.xsd |
| http://www.springframework.org/schema/osgi-compendium |
| http://www.springframework.org/schema/osgi-compendium/spring-osgi-compendium-1.2.xsd"> |
| |
| ... |
| |
| <bean class="com.springsource.configuration.properties.PropertiesController"> |
| <constructor-arg value="${driverClassName}"/> |
| <constructor-arg value="${url}"/> |
| <constructor-arg value="${username}"/> |
| <constructor-arg value="${password}"/> |
| </bean> |
| |
| <context:property-placeholder properties-ref="configAdminProperties"/> |
| |
| <osgi-compendium:cm-properties id="configAdminProperties" persistent-id="app-properties"/> |
| |
| ... |
| |
| </beans> </pre></div><p>The preceding example shows how the id <code class="literal">configAdminProperites</code> wires the <code class="literal"><context:property-placeholder></code> and <code class="literal"><osgi-compendium:cm-properties></code> elements together. Based on the value of the <code class="literal">persistent-id</code> attribute, you must also deploy a properties file called <code class="literal">app-properties.properties</code> which Virgo installs as a configuration artifact.</p><div class="section" lang="en"><div class="titlepage"><div><div><h3 class="title"><a name="developing-applications-configuration-artifacts-plan"></a>Adding the Configuration Artifact to a Plan</h3></div></div></div><p>Although you can always deploy your application and associated configuration artifact using the <code class="literal">pickup</code> directory, we recommends that you group the two together in a plan, add the two artifacts to the repository, and then deploy the plan using the <code class="literal">pickup</code> directory. The following sample plan includes the two artifacts:</p><pre class="programlisting"><?xml version="1.0" encoding="UTF-8"?> |
| <plan name="multi-artifact.plan" version="1.0.0" |
| scoped="false" atomic="false" |
| xmlns="http://www.eclipse.org/virgo/schema/plan" |
| xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" |
| xsi:schemaLocation=" |
| http://www.eclipse.org/virgo/schema/plan |
| http://www.eclipse.org/virgo/schema/plan/eclipse-virgo-plan.xsd"> |
| |
| <artifact type="configuration" name="app-properties" version="0"/> |
| <artifact type="bundle" name="org.eclipse.virgo.configuration.properties" version="1.0.0"/> |
| </plan></pre><p>For additional information about plans, see <a class="link" href="ch04s03.html" title="4.3 Creating Plans">Creating Plans</a>.</p></div></div><!--Begin LoopFuse code--><script src="http://loopfuse.net/webrecorder/js/listen.js" type="text/javascript"></script><script type="text/javascript"> |
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