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Difference between revisions of "EclipseLink/UserGuide/MOXy/Type Level/Mapping to a Type or Element/Default Root Element"

(Default Root Element)
Line 55: Line 55:
 
...
 
...
 
<java-type name="Customer">
 
<java-type name="Customer">
   <xml-root-element name="customer"/>
+
   <xml-root-element/>
 
   <java-attributes>
 
   <java-attributes>
 
       <xml-element java-attribute="name"/>
 
       <xml-element java-attribute="name"/>

Revision as of 17:39, 6 January 2011

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Elug api package icon.png Key API

Default Root Element

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 Customer and Address classes shown in this example:

Defaultrootelement.png

These classes correspond to the XML schema shown in this example. The schema contains a top-level element of type "customer-type", therefore our Customer class will need to have a default root element specified.

<xsd:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
   <xsd:complexType name="address-type">
      <xsd:sequence>
         <element name="street" type="xsd:string"/>
         <element name="city" type="xsd:string"/>
      </xsd:sequence>
   </xsd:complexType>
 
   <xsd:element name="customer" type="customer-type"/>
 
   <xsd:complexType name="customer-type">
      <xsd:sequence>
         <xsd:element name="name" type="xsd:string"/>
         <xsd:element name="billing-address" type="address-type"/>
         <xsd:element name="shipping-address" type="address-type"/>
      </xsd:sequence>
   </xsd:complexType>
</xsd:schema>

The following example shows how to annotate your Java class to specify a default root element. All that is needed is the standard JAXB @XmlRootElement annotation.

@XmlRootElement
public class Customer {
   private String name;
   private Address billingAddress;
   private Address shippingAddress;
 
   ...
}

The example below shows how specify a default root element in EclipseLink's OXM metadata format.

...
<java-type name="Customer">
   <xml-root-element/>
   <java-attributes>
      <xml-element java-attribute="name"/>
      <xml-element java-attribute="billingAddress" name="billing-address"/>
      <xml-element java-attribute="shippingAddress" name="shipping-address"/>
   </java-attributes>
</java-type>
...



Customizing the Default Root Element

In the above example, our class is called Customer, and our root element name in XML is customer. By default, when @XmlRootElement 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:

@XmlRootElement(name="my-customer")
public class Customer {
   private String name;
   private Address billingAddress;
   private Address shippingAddress;
 
   ...
}
Idea.png
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) 2.2 Specification.




How EclipseLink uses the Default Root Element

When an instance of the Customer class is persisted to XML, the EclipseLink runtime performs the following:

  • Gets the default root element. The Customer class instance corresponds to the root of the XML document. The EclipseLink runtime uses the default root element (customer) 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.
<customer>
   <name>...</name>
</customer>
  • When the EclipseLink runtime encounters an object attribute such as billingAddress, it checks the mapping associated with it to determine with what element (billing-address) to continue.
<customer>
   <name>...</name>
   <billing-address/>
</customer>
  • The EclipseLink runtime checks the mapping's reference descriptor (Address) to determine what attributes to persist.
<customer>
   <name>...</name>
   <billing-address>
      <street>...</street>
      <city>...</city>
   </billing-address>
</customer>


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Version: 2.2.0
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