juneau-doc/docs/Topics/03.juneau-marshall-rdf/01.RdfDetails/04.Namespaces.html

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Namespaces

<p>
	You'll notice in the previous example that Juneau namespaces are used to represent bean property names.
	These are used by default when namespaces are not explicitly specified.
</p>
<p>
	The <c>juneau</c> namespace is used for generic names for objects that don't have namespaces 
	associated with them.
</p>
<p>
	The <c>juneaubp</c> namespace is used on bean properties that don't have namespaces associated with 
	them.
</p>
<p>
	The easiest way to specify namespaces is through annotations.
	In this example, we're going to associate the prefix <c>'per'</c> to our bean class and all properties 
	of this class.
	We do this by adding the following annotation to our class:
</p>
<p class='bpcode w800'>
	<ja>@Rdf</ja>(prefix=<js>"per"</js>)
	<jk>public class</jk> Person {
</p>
<p>
	In general, the best approach is to define the namespace URIs at the package level using a 
	<c>package-info.java</c> class, like so:
</p>
<p class='bpcode w800'>
	<jc>// RDF namespaces used in this package</jc>
	<ja>@RdfSchema</ja>(
		prefix=<js>"ab"</js>,
		rdfNs={
			<ja>@RdfNs</ja>(prefix=<js>"ab"</js>, namespaceURI=<js>"http://www.apache.org/addressBook/"</js>),
			<ja>@RdfNs</ja>(prefix=<js>"per"</js>, namespaceURI=<js>"http://www.apache.org/person/"</js>),
			<ja>@RdfNs</ja>(prefix=<js>"addr"</js>, namespaceURI=<js>"http://www.apache.org/address/"</js>),
			<ja>@RdfNs</ja>(prefix=<js>"mail"</js>, namespaceURI=<js>"http://www.apache.org/mail/"</js>)
		}
	)
	<jk>package</jk> org.apache.juneau.sample.addressbook;
	<jk>import</jk> org.apache.juneau.xml.annotation.*;
</p>
<p>
	This assigns a default prefix of <js>"ab"</js> for all classes and properties within the project, and 
	specifies various other prefixes used within this project.
</p>
<p>
	Now when we rerun the sample code, we'll get the following:
</p>
<p class='bpcode w800'>
	<xt>&lt;rdf:RDF</xt>
	    <xa>xmlns:rdf</xa>=<xs>"http://www.w3.org/1999/02/22-rdf-syntax-ns#"</xs>
	    <xa>xmlns:j</xa>=<xs>"http://www.apache.org/juneau/"</xs>
	    <xa>xmlns:jp</xa>=<xs>"http://www.apache.org/juneaubp/"</xs>
	    <xa>xmlns:per</xa>=<xs>"http://www.apache.org/person/"</xs><xt>&gt;</xt>
	   <xt>&lt;rdf:Description&gt;</xt>
	      <xt>&lt;per:id&gt;</xt>1<xt>&lt;/per:id&gt;</xt>
	      <xt>&lt;per:name&gt;</xt>John Smith<xt>&lt;/per:name&gt;</xt>
	   <xt>&lt;/rdf:Description&gt;</xt>
	<xt>&lt;/rdf:RDF&gt;</xt>
</p>
<p>
	Namespace auto-detection ({@link oaj.xml.XmlSerializer#XML_autoDetectNamespaces}) is 
	enabled on serializers by default.
	This causes the serializer to make a first-pass over the data structure to look for namespaces.
	In high-performance environments, you may want to consider disabling auto-detection and providing an 
	explicit list of namespaces to the serializer to avoid this scanning step.
</p>
<p class='bpcode w800'>
	<jc>// Create a new serializer, but manually specify the namespaces.</jc>
	RdfSerializer s = RdfSerializer.<jsm>create</jsm>()
		.xmlabbrev()
		.set(RdfProperties.<jsf>RDF_rdfxml_tab</jsf>, 3)
		.autoDetectNamespaces(<jk>false</jk>)
		.namespaces(<js>"{per:'http://www.apache.org/person/'}"</js>)
		.build();
</p>
<p>
	This code change will produce the same output as before, but will perform slightly better since it doesn't 
	have to crawl the POJO tree before serializing the result.
</p>