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Difference between revisions of "EclipseLink/UserGuide/MOXy/Advanced XML Schema Concepts/Substitution Groups and Choices"

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{{EclipseLink_UserGuide
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'''[[Image:Elug_draft_icon.png|Warning]] This page is obsolete. Please see ''[http://www.eclipse.org/eclipselink/documentation/2.4/ Developing JAXB Applications Using EclipseLink MOXy]'' for current information.'''
|info=y
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|api=y
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|apis=* [http://www.eclipse.org/eclipselink/api/latest/org/eclipse/persistence/mappings/XmlElementRef.html XmlElementRef]
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* [http://www.eclipse.org/eclipselink/api/latest/org/eclipse/persistence/mappings/XXmlRootElement.html XXmlRootElement]
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}}
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==Substitution Groups ==
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With JAXB, you can use the element ''name'', instead of using the '''xsi:type''' attribute, to represent inheritance by using XML schema '''substitution groups'''. JAXB leverages existing XML schema concepts to produce very portable XML documents. 
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In this example, the Java model contains an abstract superclass for all types of contact information:
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<source lang="Java">
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package blog.inheritance;
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public abstract class ContactInfo {
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}
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</source>
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The '''Address''' and '''PhoneNumber''' classes are the concrete implementations of '''ContactInfo'''.  Both classes use the '''@XmlRootElement''' annotation because the element name is used as the inheritance indicator.
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<source lang="Java">
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package blog.inheritance;
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import javax.xml.bind.annotation.XmlRootElement;
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@XmlRootElement
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public class Address extends ContactInfo {
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    private String street;
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    public String getStreet() {
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        return street;
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    }
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    public void setStreet(String street) {
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        this.street = street;
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    }
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}
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@XmlRootElement
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public class PhoneNumber extends ContactInfo {
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}
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</source>
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Because the '''Customer''' object can have different types of contact information, the property refers to the superclass. The '''contactInfo''' property contains the '''@XmlElementRef''' annotation to specify that the value type will be derived from the element name (and namespace URI).
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<source lang="Java">
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package blog.inheritance;
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import javax.xml.bind.annotation.XmlElementRef;
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import javax.xml.bind.annotation.XmlRootElement;
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@XmlRootElement
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public class Customer {
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    private ContactInfo contactInfo;
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    @XmlElementRef
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    public ContactInfo getContactInfo() {
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        return contactInfo;
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    }
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    public void setContactInfo(ContactInfo contactInfo) {
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        this.contactInfo = contactInfo;
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    }
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}
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</source>
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This schema represents the JAXB view of the object model. The schema type inheritance matches the Java class inheritance. 
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<source lang="xml">
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<xs:schema version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema">
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    <xs:element name="customer" type="customer"/>
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    <xs:element name="contactInfo" type="contactInfo"/>
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    <xs:element name="address" type="address"
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        substitutionGroup="contactInfo"/>
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    <xs:element name="phoneNumber" type="phoneNumber"
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        substitutionGroup="contactInfo"/>
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    <xs:complexType name="customer">
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        <xs:sequence>
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            <xs:element ref="contactInfo"/>
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        </xs:sequence>
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    </xs:complexType>
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    <xs:complexType name="contactInfo" abstract="true">
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        <xs:sequence/>
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    </xs:complexType>
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    <xs:complexType name="address">
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        <xs:complexContent>
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            <xs:extension base="contactInfo">
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                <xs:sequence>
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                    <xs:element name="street" type="xs:string" minOccurs="0"/>
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                </xs:sequence>
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            </xs:extension>
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        </xs:complexContent>
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    </xs:complexType>
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    <xs:complexType name="phoneNumber">
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        <xs:complexContent>
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            <xs:extension base="contactInfo">
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                <xs:sequence/>
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            </xs:extension>
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        </xs:complexContent>
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    </xs:complexType>
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</xs:schema>
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</source>
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Notice that each '''type''' has a corresponding global element.  Additionally, the '''address''' and '''phoneNumber''' elements may be substituted for the '''contactInfo''' element.
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==Example ==
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This example code demonstrates using the '''xsi:type''' attribute to represent inheritance:
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<source lang="Java">
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package blog.inheritance;
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import javax.xml.bind.JAXBContext;
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import javax.xml.bind.Marshaller;
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public class Demo {
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    public static void main(String[] args) throws Exception {
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        Customer customer = new Customer();
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        Address address = new Address();
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        address.setStreet("1 A Street");
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        customer.setContactInfo(address);
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        JAXBContext jc = JAXBContext.newInstance(Customer.class, Address.class, PhoneNumber.class);
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        Marshaller marshaller = jc.createMarshaller();
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        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
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        marshaller.marshal(customer, System.out);
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    }
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}
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The example produces the following XML:
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<source lang="xml">
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<customer>
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    <address>
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        <street>1 A Street</street>
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    </address>
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</customer>
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</source>
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Notice that the '''Address''' object is marshalled to the '''address''' element.
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{{EclipseLink_MOXy
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|previous=[[EclipseLink/UserGuide/MOXy/Advanced_XML_Schema_Concepts/Handling_Null_Values|Handling Null Values]]
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|next    =[[EclipseLink/UserGuide/MOXy/Advanced_XML_Schema_Concepts/Wildcard_Content|Wildcard Content]]
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|up      =[[EclipseLink/UserGuide/MOXy/Advanced XML Schema Concepts|Advanced XML Schema Concepts]]
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|version=2.2.0 DRAFT
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}}
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Latest revision as of 13:12, 30 January 2013

Warning This page is obsolete. Please see Developing JAXB Applications Using EclipseLink MOXy for current information.