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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"><!--NewPage--><HTML><HEAD><!-- Generated by javadoc (build 1.5.0_14) on Mon Jan 28 05:46:59 PST 2008 --><TITLE>XmlElementRef (Java EE 5)</TITLE><META NAME="keywords" CONTENT="javax.xml.bind.annotation.XmlElementRef class"><LINK REL ="stylesheet" TYPE="text/css" HREF="../../../../stylesheet.css" TITLE="Style"><SCRIPT type="text/javascript">function windowTitle(){ parent.document.title="XmlElementRef (Java EE 5)";}</SCRIPT><NOSCRIPT></NOSCRIPT></HEAD><BODY BGCOLOR="white" onload="windowTitle();"><!-- ========= START OF TOP NAVBAR ======= --><A NAME="navbar_top"><!-- --></A><A HREF="#skip-navbar_top" title="Skip navigation links"></A><TABLE BORDER="0" WIDTH="100%" CELLPADDING="1" CELLSPACING="0" SUMMARY=""><TR><TD COLSPAN=2 BGCOLOR="#EEEEFF" CLASS="NavBarCell1"><A NAME="navbar_top_firstrow"><!-- --></A><TABLE BORDER="0" CELLPADDING="0" CELLSPACING="3" SUMMARY=""> <TR ALIGN="center" VALIGN="top"> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../overview-summary.html"><FONT CLASS="NavBarFont1"><B>Overview</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-summary.html"><FONT CLASS="NavBarFont1"><B>Package</B></FONT></A> </TD> <TD BGCOLOR="#FFFFFF" CLASS="NavBarCell1Rev"> <FONT CLASS="NavBarFont1Rev"><B>Class</B></FONT> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="package-tree.html"><FONT CLASS="NavBarFont1"><B>Tree</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../deprecated-list.html"><FONT CLASS="NavBarFont1"><B>Deprecated</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../index-all.html"><FONT CLASS="NavBarFont1"><B>Index</B></FONT></A> </TD> <TD BGCOLOR="#EEEEFF" CLASS="NavBarCell1"> <A HREF="../../../../help-doc.html"><FONT CLASS="NavBarFont1"><B>Help</B></FONT></A> </TD> </TR></TABLE></TD><TD ALIGN="right" VALIGN="top" ROWSPAN=3><EM></EM></TD></TR><TR><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../../../javax/xml/bind/annotation/XmlElementDecl.GLOBAL.html" title="class in javax.xml.bind.annotation"><B>PREV CLASS</B></A> <A HREF="../../../../javax/xml/bind/annotation/XmlElementRef.DEFAULT.html" title="class in javax.xml.bind.annotation"><B>NEXT CLASS</B></A></FONT></TD><TD BGCOLOR="white" CLASS="NavBarCell2"><FONT SIZE="-2"> <A HREF="../../../../index.html?javax/xml/bind/annotation/XmlElementRef.html" target="_top"><B>FRAMES</B></A> <A HREF="XmlElementRef.html" target="_top"><B>NO FRAMES</B></A> <SCRIPT type="text/javascript"> <!-- if(window==top) { document.writeln('<A HREF="../../../../allclasses-noframe.html"><B>All Classes</B></A>'); } //--></SCRIPT><NOSCRIPT> <A HREF="../../../../allclasses-noframe.html"><B>All Classes</B></A></NOSCRIPT></FONT></TD></TR><TR><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2"> SUMMARY: REQUIRED | <A HREF="#annotation_type_optional_element_summary">OPTIONAL</A></FONT></TD><TD VALIGN="top" CLASS="NavBarCell3"><FONT SIZE="-2">DETAIL: <A HREF="#annotation_type_element_detail">ELEMENT</A></FONT></TD></TR></TABLE><A NAME="skip-navbar_top"></A><!-- ========= END OF TOP NAVBAR ========= --><HR><!-- ======== START OF CLASS DATA ======== --><H2><FONT SIZE="-1">javax.xml.bind.annotation</FONT><BR>Annotation Type XmlElementRef</H2><HR><DL><DT><PRE><FONT SIZE="-1"><A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/Retention.html" title="class or interface in java.lang.annotation">@Retention</A>(<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/Retention.html#value()" title="class or interface in java.lang.annotation">value</A>=<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/RetentionPolicy.html#RUNTIME" title="class or interface in java.lang.annotation">RUNTIME</A>)<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/Target.html" title="class or interface in java.lang.annotation">@Target</A>(<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/Target.html#value()" title="class or interface in java.lang.annotation">value</A>={<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/ElementType.html#FIELD" title="class or interface in java.lang.annotation">FIELD</A>,<A HREF="http://java.sun.com/j2se/1.5/docs/api/java/lang/annotation/ElementType.html#METHOD" title="class or interface in java.lang.annotation">METHOD</A>})</FONT>public @interface <B>XmlElementRef</B></DL></PRE><P><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 <A HREF="../../../../javax/xml/bind/annotation/XmlElementRefs.html" title="annotation in javax.xml.bind.annotation"><CODE>XmlElementRefs</CODE></A> <p> This annotation dynamically associates an XML element name with the JavaBean property. When a JavaBean property is annotated with <A HREF="../../../../javax/xml/bind/annotation/XmlElement.html" title="annotation in javax.xml.bind.annotation"><CODE>XmlElement</CODE></A>, 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 <A HREF="../../../../javax/xml/bind/annotation/XmlElementDecl.html" title="annotation in javax.xml.bind.annotation"><CODE>XmlElementDecl</CODE></A> 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 <A HREF="../../../../javax/xml/bind/JAXBElement.html" title="class in javax.xml.bind"><CODE>JAXBElement</CODE></A>, 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 <A HREF="../../../../javax/xml/bind/JAXBElement.html" title="class in javax.xml.bind"><CODE>JAXBElement</CODE></A>, then the type referenced by the property or field must be annotated with <A HREF="../../../../javax/xml/bind/annotation/XmlRootElement.html" title="annotation in javax.xml.bind.annotation"><CODE>XmlRootElement</CODE></A>. </li> <li> This annotation can be used with the following annotations: <A HREF="../../../../javax/xml/bind/annotation/XmlElementWrapper.html" title="annotation in javax.xml.bind.annotation"><CODE>XmlElementWrapper</CODE></A>, <A HREF="../../../../javax/xml/bind/annotation/adapters/XmlJavaTypeAdapter.html" title="annotation in javax.xml.bind.annotation.adapters"><CODE>XmlJavaTypeAdapter</CODE></A>. </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 <A HREF="../../../../javax/xml/bind/annotation/XmlRootElement.html" title="annotation in javax.xml.bind.annotation"><CODE>XmlRootElement</CODE></A>. 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 <A HREF="../../../../javax/xml/bind/annotation/XmlElementRef.html#type()"><CODE>type()</CODE></A>is ⌨️ 快捷键说明
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