/*
* Copyright 2005-2006 Sun Microsystems, Inc. All Rights Reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Sun designates this
* particular file as subject to the "Classpath" exception as provided
* by Sun in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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*/
package javax.xml.bind.annotation;
import javax.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;
/**
* <p>
* Maps a JavaBean property to a XML element derived from property's type.
* <p>
* <b>Usage</b>
* <p>
* <tt>@XmlElementRef</tt> 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.
*
* <h3> XML Schema substitution group support </h3>
* 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 JAXB 2.0 specification). An
* element property method signature is of the form:
* <pre><xmp>
* public void setTerm(JAXBElement<? extends Operator>);
* public JAXBElement<? extends Operator> getTerm();
* </xmp></pre>
* <p>
* An element factory method annotated with {@link XmlElementDecl} is
* used to create a <tt>JAXBElement</tt> instance, containing an XML
* element name. The presence of @XmlElementRef annotation on an
* element property indicates that the element name from <tt>JAXBElement</tt>
* 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 javax.xml.bind.JAXBElement}, then
* <tt>@XmlElementRef}.name()</tt> and <tt>@XmlElementRef.namespace()</tt> 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 javax.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 javax.xml.bind.package javadoc for
* additional common information.</p>
*
* <p><b>Example 1: </b>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 {
* ...
* }
*
* <!-- 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><xmp>
* <target>
* <jar>
* ....
* </jar>
* <javac>
* ....
* </javac>
* </target>
* </xmp></pre>
* <p>
* It is not an error to have a class that extends <tt>Task</tt>
* 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>
* <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 JAXB2.0
*/
@Retention(RUNTIME)
@Target({FIELD,METHOD})
public @interface XmlElementRef {
/**
* 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 {@link #name()} are used to determine the
* XML element for the JavaBean property.
*
* <p> If <tt>type()</tt> is <tt>JAXBElement.class</tt> , then
* <tt>namespace()</tt> and <tt>name()</tt>
* 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 <tt>JAXBElement.class</tt>, 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 <tt>type()</tt> is not <tt>JAXBElement.class</tt>, then
* this value must be "".
*
*/
String namespace() default "";
/**
*
* @see #namespace()
*/
String name() default "##default";
/**
* Used in {@link XmlElementRef#type()} to
* signal that the type be inferred from the signature
* of the property.
*/
static final class DEFAULT {}
}