- Roman Grigoriadi (Oracle Corporation)
/*
* Copyright (c) 2004, 2020 Oracle and/or its affiliates. All rights reserved.
*
* This program and the accompanying materials are made available under the
* terms of the Eclipse Distribution License v. 1.0, which is available at
* http://www.eclipse.org/org/documents/edl-v10.php.
*
* SPDX-License-Identifier: BSD-3-Clause
*/
package jakarta.xml.bind.annotation;
import jakarta.xml.bind.annotation.adapters.XmlJavaTypeAdapter;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
import static java.lang.annotation.ElementType.FIELD;
import static java.lang.annotation.ElementType.METHOD;
Maps a JavaBean property to a XML element derived from property's type.
Usage
@XmlElementRef annotation can be used with a JavaBean property or from within XmlElementRefs
This annotation dynamically associates an XML element name with the JavaBean property. When a JavaBean property is annotated with XmlElement, the XML element name is statically derived from the JavaBean property name. However, when this annotation is used, the XML element name is derived from the instance of the type of the JavaBean property at runtime.
XML Schema substitution group support
XML Schema allows a XML document author to use XML element names
that were not statically specified in the content model of a
schema using substitution groups. Schema derived code provides
support for substitution groups using an element property,
(section 5.5.5, "Element Property" of Jakarta XML Binding specification). An
element property method signature is of the form:
public void setTerm(JAXBElement<? extends Operator>);
public JAXBElement<? extends Operator> getTerm();
An element factory method annotated with XmlElementDecl is used to create a JAXBElement instance, containing an XML element name. The presence of @XmlElementRef annotation on an element property indicates that the element name from JAXBElement instance be used instead of deriving an XML element name from the JavaBean property name.
The usage is subject to the following constraints:
- If the collection item type (for collection property) or property type (for single valued property) is
JAXBElement, then @XmlElementRef.name() and @XmlElementRef.namespace() must point an element factory method with an @XmlElementDecl annotation in a class annotated with @XmlRegistry (usually ObjectFactory class generated by the schema compiler) :
- @XmlElementDecl.name() must equal @XmlElementRef.name()
- @XmlElementDecl.namespace() must equal @XmlElementRef.namespace().
- If the collection item type (for collection property) or property type (for single valued property) is not
JAXBElement, then the type referenced by the property or field must be annotated with XmlRootElement.
- This annotation can be used with the following annotations:
XmlElementWrapper, XmlJavaTypeAdapter.
See "Package Specification" in jakarta.xml.bind.package javadoc for
additional common information.
Example 1: Ant Task Example
The following Java class hierarchy models an Ant build
script. An Ant task corresponds to a class in the class
hierarchy. The XML element name of an Ant task is indicated by the
@XmlRootElement annotation on its corresponding class.
@XmlRootElement(name="target") class Target { // The presence of @XmlElementRef indicates that the XML // element name will be derived from the @XmlRootElement // annotation on the type (for e.g. "jar" for JarTask). @XmlElementRef List<Task> tasks; } abstract class Task { } @XmlRootElement(name="jar") class JarTask extends Task { ... } @XmlRootElement(name="javac") class JavacTask extends Task { ... }
<!-- XML Schema fragment -->
<xs:element name="target" type="Target">
<xs:complexType name="Target">
<xs:sequence>
<xs:choice maxOccurs="unbounded">
<xs:element ref="jar">
<xs:element ref="javac">
</xs:choice>
</xs:sequence>
</xs:complexType>
Thus the following code fragment:
Target target = new Target();
target.tasks.add(new JarTask());
target.tasks.add(new JavacTask());
marshal(target);
will produce the following XML output:
<target>
<jar>
....
</jar>
<javac>
....
</javac>
</target>
It is not an error to have a class that extends Task that doesn't have XmlRootElement. But they can't show up in an XML instance (because they don't have XML element names).
Example 2: XML Schema Susbstitution group support
The following example shows the annotations for XML Schema
substitution groups. The annotations and the ObjectFactory are
derived from the schema.
@XmlElement class Math { // The value of type()is // JAXBElement.class , which indicates the XML // element name ObjectFactory - in general a class marked // with @XmlRegistry. (See ObjectFactory below) // // The name() is "operator", a pointer to a // factory method annotated with a // XmlElementDecl with the name "operator". Since // "operator" is the head of a substitution group that // contains elements "add" and "sub" elements, "operator" // element can be substituted in an instance document by // elements "add" or "sub". At runtime, JAXBElement // instance contains the element name that has been // substituted in the XML document. // @XmlElementRef(type=JAXBElement.class,name="operator") JAXBElement<? extends Operator> term; } @XmlRegistry class ObjectFactory { @XmlElementDecl(name="operator") JAXBElement<Operator> createOperator(Operator o) {...} @XmlElementDecl(name="add",substitutionHeadName="operator") JAXBElement<Operator> createAdd(Operator o) {...} @XmlElementDecl(name="sub",substitutionHeadName="operator") JAXBElement<Operator> createSub(Operator o) {...} } class Operator { ... }
Thus, the following code fragment
Math m = new Math();
m.term = new ObjectFactory().createAdd(new Operator());
marshal(m);
will produce the following XML output:
<math>
<add>...</add>
</math>
Author: - Kohsuke Kawaguchi, Sun Microsystems,Inc.
- Sekhar Vajjhala, Sun Microsystems, Inc.
See Also: Since: 1.6, JAXB 2.0
/**
* <p>
* Maps a JavaBean property to a XML element derived from property's type.
* <p>
* <b>Usage</b>
* <p>
* {@code @XmlElementRef} annotation can be used with a
* JavaBean property or from within {@link XmlElementRefs}
* <p>
* This annotation dynamically associates an XML element name with the JavaBean
* property. When a JavaBean property is annotated with {@link
* XmlElement}, the XML element name is statically derived from the
* JavaBean property name. However, when this annotation is used, the
* XML element name is derived from the instance of the type of the
* JavaBean property at runtime.
*
* <h2> XML Schema substitution group support </h2>
* XML Schema allows a XML document author to use XML element names
* that were not statically specified in the content model of a
* schema using substitution groups. Schema derived code provides
* support for substitution groups using an <i>element property</i>,
* (section 5.5.5, "Element Property" of Jakarta XML Binding specification). An
* element property method signature is of the form:
* <pre>{@code
* public void setTerm(JAXBElement<? extends Operator>);
* public JAXBElement<? extends Operator> getTerm();
* }</pre>
* <p>
* An element factory method annotated with {@link XmlElementDecl} is
* used to create a {@code JAXBElement} instance, containing an XML
* element name. The presence of {@code @XmlElementRef} annotation on an
* element property indicates that the element name from {@code JAXBElement}
* instance be used instead of deriving an XML element name from the
* JavaBean property name.
*
* <p>
* The usage is subject to the following constraints:
* <ul>
* <li> If the collection item type (for collection property) or
* property type (for single valued property) is
* {@link jakarta.xml.bind.JAXBElement}, then
* {@code @XmlElementRef.name()} and {@code @XmlElementRef.namespace()} must
* point an element factory method with an @XmlElementDecl
* annotation in a class annotated with @XmlRegistry (usually
* ObjectFactory class generated by the schema compiler) :
* <ul>
* <li> @XmlElementDecl.name() must equal @XmlElementRef.name() </li>
* <li> @XmlElementDecl.namespace() must equal @XmlElementRef.namespace(). </li>
* </ul>
* </li>
* <li> If the collection item type (for collection property) or
* property type (for single valued property) is not
* {@link jakarta.xml.bind.JAXBElement}, then the type referenced by the
* property or field must be annotated with {@link XmlRootElement}. </li>
* <li> This annotation can be used with the following annotations:
* {@link XmlElementWrapper}, {@link XmlJavaTypeAdapter}.
* </ul>
*
* <p>See "Package Specification" in jakarta.xml.bind.package javadoc for
* additional common information.</p>
*
* <p><b>Example 1: Ant Task Example</b></p>
* The following Java class hierarchy models an Ant build
* script. An Ant task corresponds to a class in the class
* hierarchy. The XML element name of an Ant task is indicated by the
* @XmlRootElement annotation on its corresponding class.
* <pre>
* @XmlRootElement(name="target")
* class Target {
* // The presence of @XmlElementRef indicates that the XML
* // element name will be derived from the @XmlRootElement
* // annotation on the type (for e.g. "jar" for JarTask).
* @XmlElementRef
* List<Task> tasks;
* }
*
* abstract class Task {
* }
*
* @XmlRootElement(name="jar")
* class JarTask extends Task {
* ...
* }
*
* @XmlRootElement(name="javac")
* class JavacTask extends Task {
* ...
* }
* {@code
*
* <!-- XML Schema fragment -->
* <xs:element name="target" type="Target">
* <xs:complexType name="Target">
* <xs:sequence>
* <xs:choice maxOccurs="unbounded">
* <xs:element ref="jar">
* <xs:element ref="javac">
* </xs:choice>
* </xs:sequence>
* </xs:complexType>
*
* }</pre>
* <p>
* Thus the following code fragment:
* <pre>
* Target target = new Target();
* target.tasks.add(new JarTask());
* target.tasks.add(new JavacTask());
* marshal(target);
* </pre>
* will produce the following XML output:
* <pre>{@code
* <target>
* <jar>
* ....
* </jar>
* <javac>
* ....
* </javac>
* </target>
* }</pre>
* <p>
* It is not an error to have a class that extends {@code Task}
* that doesn't have {@link XmlRootElement}. But they can't show up in an
* XML instance (because they don't have XML element names).
*
* <p><b>Example 2: XML Schema Susbstitution group support</b>
* <p> The following example shows the annotations for XML Schema
* substitution groups. The annotations and the ObjectFactory are
* derived from the schema.
*
* <pre>
* @XmlElement
* class Math {
* // The value of {@link #type()}is
* // JAXBElement.class , which indicates the XML
* // element name ObjectFactory - in general a class marked
* // with @XmlRegistry. (See ObjectFactory below)
* //
* // The {@link #name()} is "operator", a pointer to a
* // factory method annotated with a
* // {@link XmlElementDecl} with the name "operator". Since
* // "operator" is the head of a substitution group that
* // contains elements "add" and "sub" elements, "operator"
* // element can be substituted in an instance document by
* // elements "add" or "sub". At runtime, JAXBElement
* // instance contains the element name that has been
* // substituted in the XML document.
* //
* @XmlElementRef(type=JAXBElement.class,name="operator")
* JAXBElement<? extends Operator> term;
* }
*
* @XmlRegistry
* class ObjectFactory {
* @XmlElementDecl(name="operator")
* JAXBElement<Operator> createOperator(Operator o) {...}
* @XmlElementDecl(name="add",substitutionHeadName="operator")
* JAXBElement<Operator> createAdd(Operator o) {...}
* @XmlElementDecl(name="sub",substitutionHeadName="operator")
* JAXBElement<Operator> createSub(Operator o) {...}
* }
*
* class Operator {
* ...
* }
* </pre>
* <p>
* Thus, the following code fragment
* <pre>
* Math m = new Math();
* m.term = new ObjectFactory().createAdd(new Operator());
* marshal(m);
* </pre>
* will produce the following XML output:
* <pre>{@code
* <math>
* <add>...</add>
* </math>
* }</pre>
*
*
* @author <ul><li>Kohsuke Kawaguchi, Sun Microsystems,Inc. </li><li>Sekhar Vajjhala, Sun Microsystems, Inc.</li></ul>
* @see XmlElementRefs
* @since 1.6, JAXB 2.0
*/
@Retention(RUNTIME)
@Target({FIELD,METHOD})
public @interface XmlElementRef {
The Java type being referenced.
If the value is DEFAULT.class, the type is inferred from the
the type of the JavaBean property.
/**
* The Java type being referenced.
* <p>
* If the value is DEFAULT.class, the type is inferred from the
* the type of the JavaBean property.
*/
Class type() default DEFAULT.class;
This parameter and name() are used to determine the XML element for the JavaBean property. If type() is JAXBElement.class , then namespace() and name() point to a factory method with XmlElementDecl. The XML element name is the element name from the factory method's XmlElementDecl annotation or if an element from its substitution group (of which it is a head element) has been substituted in the XML document, then the element name is from the XmlElementDecl on the substituted element.
If type() is not JAXBElement.class, then the XML element name is the XML element name statically associated with the type using the annotation XmlRootElement on the type. If the type is not annotated with an XmlElementDecl, then it is an error.
If type() is not JAXBElement.class, then this value must be "".
/**
* This parameter and {@link #name()} are used to determine the
* XML element for the JavaBean property.
*
* <p> If {@code type()} is {@code JAXBElement.class} , then
* {@code namespace()} and {@code name()}
* point to a factory method with {@link XmlElementDecl}. The XML
* element name is the element name from the factory method's
* {@link XmlElementDecl} annotation or if an element from its
* substitution group (of which it is a head element) has been
* substituted in the XML document, then the element name is from the
* {@link XmlElementDecl} on the substituted element.
*
* <p> If {@link #type()} is not {@code JAXBElement.class}, then
* the XML element name is the XML element name statically
* associated with the type using the annotation {@link
* XmlRootElement} on the type. If the type is not annotated with
* an {@link XmlElementDecl}, then it is an error.
*
* <p> If {@code type()} is not {@code JAXBElement.class}, then
* this value must be "".
*
*/
String namespace() default "";
See Also: - namespace()
/**
*
* @see #namespace()
*/
String name() default "##default";
Used in XmlElementRef.type() to signal that the type be inferred from the signature of the property. /**
* Used in {@link XmlElementRef#type()} to
* signal that the type be inferred from the signature
* of the property.
*/
static final class DEFAULT {}
Customize the element declaration to be required.
If required() is true, then Javabean property is mapped to
an XML schema element declaration with minOccurs="1".
maxOccurs is "1" for a single valued property and "unbounded"
for a multivalued property.
If required() is false, then the Javabean property is mapped
to XML Schema element declaration with minOccurs="0".
maxOccurs is "1" for a single valued property and "unbounded"
for a multivalued property.
For compatibility with Jakarta XML Binding, this property defaults to true, despite the fact that XmlElement.required() defaults to false.
Since: 1.7, JAXB 2.2
/**
* Customize the element declaration to be required.
* <p>
* If required() is true, then Javabean property is mapped to
* an XML schema element declaration with minOccurs="1".
* maxOccurs is "1" for a single valued property and "unbounded"
* for a multivalued property.
*
* <p>
* If required() is false, then the Javabean property is mapped
* to XML Schema element declaration with minOccurs="0".
* maxOccurs is "1" for a single valued property and "unbounded"
* for a multivalued property.
*
* <p>
* For compatibility with Jakarta XML Binding, this property defaults to {@code true},
* despite the fact that {@link XmlElement#required()} defaults to false.
*
* @since 1.7, JAXB 2.2
*/
boolean required() default true;
}