javax.xml.bind.annotation
注释类型 XmlIDREF

@Retention(value=RUNTIME)
@Target(value={FIELD,METHOD})
public @interface XmlIDREF

将 JavaBean 属性映射到 XML IDREF。

要在 XML 序列化然后反序列化这一过程中保持对象图形的引用完整性，需要通过使用引用或容器适当地对对象引用进行编组。注释 @XmlID 和 @XmlIDREF 一起使用时允许通过容器或引用来实现 JavaBean 属性类型的自定义映射。

用法

• JavaBean 属性
• 非 static、非 transient 字段

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

用法受到以下约束的限制：

• 如果字段或属性的类型是一个 collection 类型，则集合项类型必须包含一个用 @XmlID 注释的属性或字段。
• 如果字段或属性的类型是 single valued，则属性或字段的类型必须包含一个用 @XmlID 注释的属性或字段。

  注：如果集合项类型或属性的类型（用于非 collection 类型）是 java.lang.Object，则该实例必须包含一个用 @XmlID 属性注释的属性/字段。

• 此注释可与以下注释一起使用：XmlElement、XmlAttribute、XmlList 和 XmlElements。

示例：将 JavaBean 属性映射到 xs:IDREF（即通过引用而不是通过包含）。

   //EXAMPLE: Code fragment
   public class Shipping {
       @XmlIDREF public Customer getCustomer();
       public void setCustomer(Customer customer);
       ....
    }

   <!-- Example: XML Schema fragment -->
   <xs:complexType name="Shipping">
     <xs:complexContent>
       <xs:sequence>
         <xs:element name="customer" type="xs:IDREF"/>
         ....
       </xs:sequence>
     </xs:complexContent>
   </xs:complexType>

 

示例 2：以下是一个对比容器与引用的完整示例。

    // By default, Customer maps to complex type xs:Customer
    public class Customer {
        
        // map JavaBean property type to xs:ID
        @XmlID public String getCustomerID();
        public void setCustomerID(String id);

        // .... other properties not shown 
    }


   // By default, Invoice maps to a complex type xs:Invoice 
   public class Invoice {
    
       // map by reference
       @XmlIDREF public Customer getCustomer();       
       public void setCustomer(Customer customer);

      // .... other properties not shown here
   }

   // By default, Shipping maps to complex type xs:Shipping
   public class Shipping {

       // map by reference
       @XmlIDREF public Customer getCustomer();       
       public void setCustomer(Customer customer);
   }

   // at least one class must reference Customer by containment;
   // Customer instances won't be marshalled.
   @XmlElement(name="CustomerData")
   public class CustomerData {
       // map reference to Customer by containment by default.
       public Customer getCustomer();

       // maps reference to Shipping by containment by default. 
       public Shipping getShipping();     

       // maps reference to Invoice by containment by default. 
       public Invoice getInvoice();     
   }

   <!-- XML Schema mapping for above code frament -->

   <xs:complexType name="Invoice">
     <xs:complexContent>
       <xs:sequence>
         <xs:element name="customer" type="xs:IDREF"/>
         ....
       </xs:sequence>
     </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="Shipping">
     <xs:complexContent>
       <xs:sequence>
         <xs:element name="customer" type="xs:IDREF"/>
         ....
       </xs:sequence>
     </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="Customer">
     <xs:complexContent>
       <xs:sequence>
         ....
       </xs:sequence>
       <xs:attribute name="CustomerID" type="xs:ID"/>
     </xs:complexContent>
   </xs:complexType>

   <xs:complexType name="CustomerData">
     <xs:complexContent>
       <xs:sequence>
         <xs:element name="customer" type="xs:Customer"/>
         <xs:element name="shipping" type="xs:Shipping"/>
         <xs:element name="invoice"  type="xs:Invoice"/>
       </xs:sequence>
     </xs:complexContent>
   </xs:complexType>

   <xs:element name"customerData" type="xs:CustomerData"/>

   <!-- Instance document conforming to the above XML Schema -->
    <customerData>
       <customer customerID="Alice">
           ....
       </customer>

       <shipping customer="Alice">
           ....
       </shipping>
         
       <invoice customer="Alice">
           ....
       </invoice>
   </customerData>

 

示例 3：将列表映射到 IDREF 类型的重复元素。

     // Code fragment
     public class Shipping {
         @XmlIDREF
         @XmlElement(name="Alice")
             public List customers;
     }

     <!-- XML schema fragment -->
     <xs:complexType name="Shipping">
       <xs:sequence>
         <xs:choice minOccurs="0" maxOccurs="unbounded">
           <xs:element name="Alice" type="xs:IDREF"/>
         </xs:choice>
       </xs:sequence>
     </xs:complexType> 
 

示例 4：将列表映射到 IDREF 类型的元素列表。

     //Code fragment
     public class Shipping {
         @XmlIDREF
         @XmlElements(
             @XmlElement(name="Alice", type="Customer.class")
              @XmlElement(name="John", type="InternationalCustomer.class")
         public List customers;
     }

     <!-- XML Schema fragment -->
     <xs:complexType name="Shipping">
       <xs:sequence>
         <xs:choice minOccurs="0" maxOccurs="unbounded">
           <xs:element name="Alice" type="xs:IDREF"/>
           <xs:element name="John" type="xs:IDREF"/>
         </xs:choice>
       </xs:sequence>
     </xs:complexType> 
 

从以下版本开始：

JAXB2.0

另请参见：

XmlID

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