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 <article class="doc">
 <h1 class="page">Apache Felix Metatype Service</h1>
 <div id="preamble">
 <div class="sectionbody">
 <div class="paragraph">
 <p>The OSGi Metatype specification provides a unified way to describe metadata about services and a Java interface to retrieve and manipulate such information.
 This information can optionally be localized, thus allowing the developer to provide human-readable metadata descriptions in multiple languages.
 The specification defines a rich dynamic typing system to describe service attributes in a precise way, which makes it possible to dynamically create user interfaces to configure services.</p>
 </div>
 <div class="paragraph">
 <p>The simplest way to specify service metatype information is to add one or more XML files in the <code>OSGI-INF/metatype</code> folder.
 For example, the <code>OSGI-INF/metatype/metatype.xml</code> file included in the <a href="apache-felix-file-install.html" class="page">Apache Felix File Install</a> subproject is as follows:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre>&lt;?xml version="1.0" encoding="UTF-8"?&gt;
 &lt;metatype:MetaData xmlns:metatype="http://www.osgi.org/xmlns/metatype/v1.0.0"&gt;

   &lt;OCD description="FileInstaller" name="org.apache.felix.fileinstall" id="org.apache.felix.fileinstall"&gt;

     &lt;AD name="Poll directory"  id="felix.fileinstall.dir" required="true" type="String" default="load"/&gt;
     &lt;AD name="Poll interval"  id="felix.fileinstall.poll" required="false" type="String" default="5000"/&gt;
     &lt;AD name="Debug"  id="felix.fileinstall.debug" required="false" type="String" default="-1"/&gt;
     &lt;AD name="Start new bundles?"  id="felix.fileinstall.bundles.new.start" required="false" type="String" default="true"/&gt;

   &lt;/OCD&gt;

     &lt;Designate pid="org.apache.felix.fileinstall"&gt;
         &lt;Object ocdref="org.apache.felix.fileinstall"/&gt;
     &lt;/Designate&gt;

 &lt;/metatype:MetaData&gt;</pre>
 </div>
 </div>
 <div class="paragraph">
 <p>The main elements of this simple example are:</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p><em>OCD</em>, Object Class Definition;
 contains the information about a set of attributes.</p>
 </li>
 <li>
 <p><em>AD</em>, Attribute Definition;
 describes an attribute (name, description, unique id, type, cardinality, default value, &#8230;&#8203;).</p>
 </li>
 <li>
 <p><em>Designate</em>, defines the association between an Object Class Definition and a pid;
 the pid can be a reference to a factory or a singleton configuration object.</p>
 </li>
 </ul>
 </div>
 <div class="paragraph">
 <p>The following types are supported by the specification:</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p>String</p>
 </li>
 <li>
 <p>Long</p>
 </li>
 <li>
 <p>Double</p>
 </li>
 <li>
 <p>Float</p>
 </li>
 <li>
 <p>Integer</p>
 </li>
 <li>
 <p>Byte</p>
 </li>
 <li>
 <p>Char</p>
 </li>
 <li>
 <p>Boolean</p>
 </li>
 <li>
 <p>Short</p>
 </li>
 </ul>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_localization"><a class="anchor" href="#_localization"></a>Localization</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>As mentioned before, it is possible to localize metatype information.
 A good example is the <a href="apache-felix-web-console.html" class="page">Apache Felix Web Console</a> subproject, which includes the following metatype information:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre>&lt;?xml version="1.0" encoding="UTF-8"?&gt;

 &lt;metatype:MetaData xmlns:metatype="http://www.osgi.org/xmlns/metatype/v1.0.0" localization="OSGI-INF/metatype/metatype"&gt;

     &lt;OCD id="org.apache.felix.webconsole.internal.servlet.OsgiManager" name="%manager.name" description="%manager.description"&gt;
         &lt;AD id="manager.root" type="String" default="/system/console" name="%manager.root.name" description="%manager.root.description"/&gt;
         &lt;AD id="default.render" type="String" default="bundles" name="%default.render.name" description="%default.render.description"/&gt;
         &lt;AD id="realm" type="String" default="OSGi Management Console" name="%realm.name" description="%realm.description"/&gt;
         &lt;AD id="username" type="String" default="admin" name="%username.name" description="%username.description"/&gt;
         &lt;AD id="password" type="String" default="admin" name="%password.name" description="%password.description"/&gt;
     &lt;/OCD&gt;

     &lt;Designate pid="org.apache.felix.webconsole.internal.servlet.OsgiManager"&gt;
         &lt;Object ocdref="org.apache.felix.webconsole.internal.servlet.OsgiManager"/&gt;
     &lt;/Designate&gt;

 &lt;/metatype:MetaData&gt;</pre>
 </div>
 </div>
 <div class="paragraph">
 <p>The key elements to write a localized metatype definition are</p>
 </div>
 <div class="ulist">
 <ul>
 <li>
 <p>The <em>localization</em> attribute, that points to the property file that localize this XML.</p>
 </li>
 <li>
 <p>The <em>%</em> notation that specifies a localizable string name.</p>
 </li>
 <li>
 <p>One or more property files defining localized strings.</p>
 </li>
 </ul>
 </div>
 <div class="paragraph">
 <p>The following example shows the localization property file of the Web Console:</p>
 </div>
 <div class="listingblock">
 <div class="content">
 <pre>manager.name = Apache Felix OSGi Management Console
 manager.description = Configuration of the Apache Felix OSGi Management Console.

 manager.root.name = Root URI
 manager.root.description = The root path to the OSGi Management Console.

 realm.name = Realm
 realm.description = The name of the HTTP Authentication Realm.

 username.name = User Name
 username.description = The name of the user allowed to access the OSGi \
  Management Console. To disable authentication clear this value.

 password.name = Password
 password.description = The password for the user allowed to access the OSGi \
  Management Console.

 default.render.name = Default Page
 default.render.description = The name of the default configuration page \
  when invoking the OSGi Management console.</pre>
 </div>
 </div>
 </div>
 </div>
 <div class="sect1">
 <h2 id="_metatype_service_api"><a class="anchor" href="#_metatype_service_api"></a>Metatype Service API</h2>
 <div class="sectionbody">
 <div class="paragraph">
 <p>Before using the Metatype Service API, it&#8217;s worth noting that this specification is not part of the OSGi core specification, so it&#8217;s not included in the standard Felix distribution.
 It is therefore necessary to download and install the additional Metatype bundle.</p>
 </div>
 <div class="paragraph">
 <p>Accessing the Metatype service is as simple as performing a lookup in the service registry:</p>
 </div>
 <div class="literalblock">
 <div class="content">
 <pre>ServiceReference metatypeRef = bundleContext.getServiceReference(MetaTypeService.class.getName());
 MetaTypeService service = (MetaTypeService) bundleContext.getService(metatypeRef);</pre>
 </div>
 </div>
 <div class="literalblock">
 <div class="content">
 <pre>MetaTypeInformation information = service.getMetaTypeInformation(myBundle);</pre>
 </div>
 </div>
 <div class="paragraph">
 <p>After retrieving the <code>MetaTypeInformation</code> object for the required bundle, we have access to all the information contained in the metatype XML definition.
 In particular, it is possible to access the ObjectClassDefinition (optionally specifying a locale):</p>
 </div>
 <div class="literalblock">
 <div class="content">
 <pre>ObjectClassDefinition ocd = information.getObjectClassDefinition(pid, locale);</pre>
 </div>
 </div>
 <div class="paragraph">
 <p>With the <code>ObjectClassDefinition</code>, it is possible to retrieve all the attribute definitions:</p>
 </div>
 <div class="literalblock">
 <div class="content">
 <pre>AttributeDefinition[] attributes = ocd.getAttributeDefinitions(ObjectClassDefinition.ALL);</pre>
 </div>
 </div>
 </div>
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