XmlRootElement (Java EE 5)

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javax.xml.bind.annotation Annotation Type XmlRootElement

@Retention(value=RUNTIME)
@Target(value=TYPE)
public @interface XmlRootElement

Implements: Annotation
@Retention(value=RUNTIME)
@Target(value=TYPE)

将类或枚举类型映射到 XML 元素。

用法

@XmlRootElement 注释可以与以下程序元素一起使用：

  • 顶层类
  • 枚举类型

有关其他公共信息，请参阅 javax.xml.bind.package javadoc 中的“包规范”。

当使用 @XmlRootElement 注释对顶层类或枚举类型进行注释时，类型值被表示为 XML 文档中的 XML 元素。

此注释可与以下注释一起使用： XmlType、XmlEnum、XmlAccessorType、 XmlAccessorOrder。

示例 1：将元素与 XML 模式类型关联 

     // Example: Code fragment
     @XmlRootElement
     class Point {
        int x;
        int y;
        Point(int _x,int _y) {x=_x;y=_y;}
     }
 
     //Example: Code fragment corresponding to XML output
     marshal( new Point(3,5), System.out);
 

     <!-- Example: XML output -->
     <point>
       <x> 3 </x>
       <y> 5 </y>
     </point>
该注释会导致在模式中生成全局元素声明。全局元素声明与类映射到的 XML 模式类型关联。 

<!-- Example:XML schema definition -->
     <xs:element name="point" type="point">
     <xs:complextype name="point">
       <xs:sequence>
         </xs:sequence></xs:complextype></xs:element><xs:element name="x" type="xs:int">
         </xs:element><xs:element name="y" type="xs:int">
       
     
 </xs:element>

示例 2：类型继承的正交性

某一类型上注释的元素声明不会被其派生类型继承。以下示例显示了这一点： 

     // Example: Code fragment
     @XmlRootElement
     class Point3D extends Point {
         int z;
         Point3D(int _x,int _y,int _z) {super(_x,_y);z=_z;}
     }

     //Example: Code fragment corresponding to XML output * 
     marshal( new Point3D(3,5,0), System.out );

     <!-- Example: XML output -->
     <!-- The element name is point3D not point -->
     <point3D>
       <x>3</x>
       <y>5</y>
       <z>0</z>
     </point3D>

     <!-- Example: XML schema definition -->
     <xs:element name="point3D" type="point3D"/>
     <xs:complexType name="point3D">
       <xs:complexContent>
         <xs:extension base="point">
           <xs:sequence>
             <xs:element name="z" type="xs:int"/>
           </xs:sequence>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
示例 3：将全局元素与该类映射到的 XML 模式类型关联。 
     //Example: Code fragment
     @XmlRootElement(name="PriceElement")
     public class USPrice {
         @XmlElement
         public java.math.BigDecimal price;
     }

     <!-- Example: XML schema definition -->
     <xs:element name="PriceElement" type="USPrice"/>
     <xs:complexType name="USPrice">
       <xs:sequence>
         <xs:element name="price" type="xs:decimal"/>
       </sequence>
     </xs:complexType>
sinceJAXB2.0
英文文档：

Maps a class or an enum type to an XML element.

Usage

The @XmlRootElement annotation can be used with the following program elements:

  • a top level class
  • an enum type

See "Package Specification" in javax.xml.bind.package javadoc for additional common information.

When a top level class or an enum type is annotated with the @XmlRootElement annotation, then its value is represented as XML element in an XML document.

This annotation can be used with the following annotations: XmlType, XmlEnum, XmlAccessorType, XmlAccessorOrder.

Example 1: Associate an element with XML Schema type 

     // Example: Code fragment
     @XmlRootElement
     class Point {
        int x;
        int y;
        Point(int _x,int _y) {x=_x;y=_y;}
     }
 
     //Example: Code fragment corresponding to XML output
     marshal( new Point(3,5), System.out);
 

     &lt;!-- Example: XML output --&gt;
     &lt;point&gt;
       &lt;x&gt; 3 &lt;/x&gt;
       &lt;y&gt; 5 &lt;/y&gt;
     &lt;/point&gt;
The annotation causes an global element declaration to be produced in the schema. The global element declaration is associated with the XML schema type to which the class is mapped. 

     &lt;!-- Example: XML schema definition --&gt;
     &lt;xs:element name="point" type="point"&gt;
     &lt;xs:complextype name="point"&gt;
       &lt;xs:sequence&gt;
         &lt;/xs:sequence&gt;&lt;/xs:complextype&gt;&lt;/xs:element&gt;&lt;xs:element name="x" type="xs:int"&gt;
         &lt;/xs:element&gt;&lt;xs:element name="y" type="xs:int"&gt;
       
     
 &lt;/xs:element&gt;

Example 2: Orthogonality to type inheritance

An element declaration annotated on a type is not inherited by its derived types. The following example shows this. 

     // Example: Code fragment
     @XmlRootElement
     class Point3D extends Point {
         int z;
         Point3D(int _x,int _y,int _z) {super(_x,_y);z=_z;}
     }

     //Example: Code fragment corresponding to XML output * 
     marshal( new Point3D(3,5,0), System.out );

     <!-- Example: XML output -->
     <!-- The element name is point3D not point -->
     <point3D>
       <x>3</x>
       <y>5</y>
       <z>0</z>
     </point3D>

     <!-- Example: XML schema definition -->
     <xs:element name="point3D" type="point3D"/>
     <xs:complexType name="point3D">
       <xs:complexContent>
         <xs:extension base="point">
           <xs:sequence>
             <xs:element name="z" type="xs:int"/>
           </xs:sequence>
         </xs:extension>
       </xs:complexContent>
     </xs:complexType>
Example 3: Associate a global element with XML Schema type to which the class is mapped. 
     //Example: Code fragment
     @XmlRootElement(name="PriceElement")
     public class USPrice {
         @XmlElement
         public java.math.BigDecimal price;
     }

     <!-- Example: XML schema definition -->
     <xs:element name="PriceElement" type="USPrice"/>
     <xs:complexType name="USPrice">
       <xs:sequence>
         <xs:element name="price" type="xs:decimal"/>
       </sequence>
     </xs:complexType>

Since:
JAXB2.0
Author:
Sekhar Vajjhala, Sun Microsystems, Inc.

Optional Element Summary
 String name
          local name of the XML element.
 String namespace
          namespace name of the XML element.
 

abstract public String namespace()
XML 元素的名称空间名。

如果该值为 "##default"，那么 XML 名称空间名派生于类 (XmlSchema) 的包。如果没有对包命名，那么 XML 名称空间是默认的空名称空间。

英文文档：

namespace

public abstract String namespace
namespace name of the XML element.

If the value is "##default", then the XML namespace name is derived from the package of the class ( XmlSchema ). If the package is unnamed, then the XML namespace is the default empty namespace.

Default:
"##default"

abstract public String name()
XML 元素的本地名称。

如果值为 "##default"，则名称派生于类名称。

英文文档：

name

public abstract String name
local name of the XML element.

If the value is "##default", then the name is derived from the class name.

Default:
"##default"
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