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<div class="sect1"><!-- infolevel="all" infotype="General" -->
<h1 class="sect1"><font face="arial, helvetica, sans-serif" color="#330099">Defining the Default Root Element</font></h1>
<p>At least one of your mapped classes must have a default root element defined. This tells EclipseLink what the top-level root of your XML document will be. Consider the <strong>Customer</strong> and <strong>Address</strong> classes shown in <a href="#CIHDBEDH">Figure 3-1</a>:</p>
<div class="figure"><a id="CIHDBEDH" name="CIHDBEDH"></a><a id="TLJAX187" name="TLJAX187"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Figure 3-1 Sample Mapped Classes</font></em></strong></p>
<img src="img/defaultrootelement.gif" alt="Sample Mapped Classes" title="Sample Mapped Classes" longdesc="img_text/defaultrootelement.htm" /><br />
<a id="sthref57" name="sthref57" href="img_text/defaultrootelement.htm">Description of "Figure 3-1 Sample Mapped Classes"</a><br />
<br /></div>
<!-- class="figure" -->
<p>These classes correspond to the XML schema shown in <a href="#CIHFBEII">Example 3-1</a>. The schema contains a top-level element of type <code>customer-type</code>, therefore our <strong>Customer</strong> class will need to have a default root element specified.</p>
<div class="example"><a id="CIHFBEII" name="CIHFBEII"></a><a id="TLJAX188" name="TLJAX188"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-1 Sample XML Schema</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;xsd:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"&gt;
&lt;xsd:complexType name="address-type"&gt;
&lt;xsd:sequence&gt;
&lt;element name="street" type="xsd:string"/&gt;
&lt;element name="city" type="xsd:string"/&gt;
&lt;/xsd:sequence&gt;
&lt;/xsd:complexType&gt;
&lt;xsd:element <strong>name="customer" type="customer-type"</strong>/&gt;
&lt;xsd:complexType name="customer-type"&gt;
&lt;xsd:sequence&gt;
&lt;xsd:element name="name" type="xsd:string"/&gt;
&lt;xsd:element name="billing-address" type="address-type"/&gt;
&lt;xsd:element name="shipping-address" type="address-type"/&gt;
&lt;/xsd:sequence&gt;
&lt;/xsd:complexType&gt;
&lt;/xsd:schema&gt;
</pre></div>
<!-- class="example" -->
<p><a href="#CIHGHJDA">Example 3-2</a> shows how to annotate your Java class to specify a default root element. All that is needed is the standard JAXB <code>@XmlRootElement</code> annotation.</p>
<div class="example"><a id="CIHGHJDA" name="CIHGHJDA"></a><a id="TLJAX189" name="TLJAX189"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-2 Using the @XmlRootElement Annotation</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
package example;
import javax.xml.bind.annotation.*;
<strong>@XmlRootElement</strong>
public class Customer {
private String name;
@XmlElement(name="billing-address")
private Address billingAddress;
@XmlElement(name="shipping-address")
private Address shippingAddress;
...
}
</pre></div>
<!-- class="example" -->
<p><a href="#CIHFDJCE">Example 3-3</a> shows how specify a default root element in EclipseLink's OXM metadata format.</p>
<div class="example"><a id="CIHFDJCE" name="CIHFDJCE"></a><a id="TLJAX190" name="TLJAX190"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-3 Specifying a Default Root Element</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
...
&lt;java-type name="Customer"&gt;
&lt;<strong>xml-root-element</strong>/&gt;
&lt;java-attributes&gt;
&lt;xml-element java-attribute="name"/&gt;
&lt;xml-element java-attribute="billingAddress" name="billing-address"/&gt;
&lt;xml-element java-attribute="shippingAddress" name="shipping-address"/&gt;
&lt;/java-attributes&gt;
&lt;/java-type&gt;
...
</pre></div>
<!-- class="example" -->
<a id="TLJAX191" name="TLJAX191"></a>
<div class="sect2"><a id="sthref58" name="sthref58"></a>
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Customizing the Default Root Element</font></h2>
<p>In <a href="#CIHGHJDA">Example 3-2</a>, our class is called <strong>Customer</strong>, and our root element name in XML is <code>customer</code>. By default, when <code>@XmlRootElement</code> is specified, the name of the class has its first letter lower-cased, and this is set as the root element name. If, however, the element name in XML is different from the Java class name, a name attribute can be included in the annotation (as in <a href="#CIHCGICI">Example 3-4</a>) or OXM metadata (as in <a href="#CIHHJIHH">Example 3-5</a>):</p>
<div class="example"><a id="CIHCGICI" name="CIHCGICI"></a><a id="TLJAX192" name="TLJAX192"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-4 Using Annotations</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
package example;
import javax.xml.bind.annotation.*;
<strong>@XmlRootElement</strong>(name="my-customer")
public class Customer {
private String name;
@XmlElement(name="billing-address")
private Address billingAddress;
@XmlElement(name="shipping-address")
private Address shippingAddress;
...
}
</pre></div>
<!-- class="example" -->
<div class="example"><a id="CIHHJIHH" name="CIHHJIHH"></a><a id="TLJAX193" name="TLJAX193"></a>
<p><strong><em><font face="arial, helvetica, sans-serif">Example 3-5 Using OXM Metadata</font></em></strong></p>
<pre xml:space="preserve" class="oac_no_warn">
...
&lt;java-type name="Customer"&gt;
<strong> &lt;xml-root-element name="my-customer"/&gt;</strong>
&lt;java-attributes&gt;
&lt;xml-element java-attribute="name"/&gt;
&lt;xml-element java-attribute="billingAddress" name="billing-address"/&gt;
&lt;xml-element java-attribute="shippingAddress" name="shipping-address"/&gt;
&lt;/java-attributes&gt;
&lt;/java-type&gt;
...
</pre></div>
<!-- class="example" -->
<p>For more information on JAXB name-binding algorithms, see "Appendix D: Binding XML Names to Java Identifiers" of the Java Architecture for XML Binding (JAXB) Specification (<code><a href="http://jcp.org/en/jsr/detail?id=222">http://jcp.org/en/jsr/detail?id=222</a></code>).</p>
</div>
<!-- class="sect2" -->
<a id="TLJAX194" name="TLJAX194"></a>
<div class="sect2"><a id="sthref59" name="sthref59"></a>
<h2 class="sect2"><font face="arial, helvetica, sans-serif" color="#330099">Understanding How EclipseLink Uses the Default Root Element</font></h2>
<p>When an instance of the <strong>Customer</strong> class is persisted to XML, the EclipseLink runtime performs the following:</p>
<ul>
<li>
<p>Gets the default root element. The <strong>Customer</strong> class instance corresponds to the root of the XML document. The EclipseLink runtime uses the default root element (<code>customer</code>) specified in either annotations or OXM to start the XML document. EclipseLink then uses the mappings on the class to marshal the object's attributes.</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;customer&gt;
&lt;name&gt;...&lt;/name&gt;
&lt;/customer&gt;
</pre></li>
<li>
<p>When the EclipseLink runtime encounters an object attribute such as <code>billingAddress</code>, it checks the mapping associated with it to determine with what element (billing-<code>address</code>) to continue.</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;customer&gt;
&lt;name&gt;...&lt;/name&gt;
&lt;billing-address/&gt;
&lt;/customer&gt;
</pre></li>
<li>
<p>The EclipseLink runtime checks the mapping's reference descriptor (<strong>Address</strong>) to determine what attributes to persist.</p>
<pre xml:space="preserve" class="oac_no_warn">
&lt;customer&gt;
&lt;name&gt;...&lt;/name&gt;
&lt;billing-address&gt;
&lt;street&gt;...&lt;/street&gt;
&lt;city&gt;...&lt;/city&gt;
&lt;/billing-address&gt;
&lt;/customer&gt;
</pre></li>
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