JAXB将@XmlElementRefs和@XmlElements转换为xs:choice

Question

我有4节课.Person类和抽象ContactInformation与Phone和Address类扩展它.

@XmlRootElement
@XmlAccessorType(XmlAccessType.NONE)
public class Person {
    @XmlElement(required = true, nillable = false)
    private String first;
    @XmlElement(required = true, nillable = false)
    private String last;
    @XmlElementWrapper(name = "contacts")
    @XmlElementRefs({
        @XmlElementRef(name = "phone", type = Phone.class, required = true),
        @XmlElementRef(name = "address", type = Address.class, required = true)
    })
    private final List<ContactInfomation> contacts = new ArrayList<>();
}

ContactInformation 仅用作容器:

public abstract class ContactInfomation { /* empty class */ }

Phone 类:

@XmlRootElement
@XmlAccessorType(XmlAccessType.NONE)
public class Phone extends ContactInfomation {
    @XmlElement(required = true, nillable = false)
    private String number;
}

和Address班级:

@XmlRootElement
@XmlAccessorType(XmlAccessType.NONE)
public class Address extends ContactInfomation {
    @XmlElement(required = true, nillable = false)
    private String country;
    @XmlElement(required = true, nillable = false)
    private String city;
}

问题是,当我换@XmlElementrefs到@XmlElements的Person类,没有任何反应.JAXB将它们映射到xs:choice.XML输出与以前相同,并schemagen生成与以前相同的模式.这是一个示例输出:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<person>
    <first>majid</first>
    <last>azimi</last>
    <contacts>
        <address>
            <country>US</country>
            <city>Los Angles</city>
        </address>
        <address>
            <country>US</country>
            <city>New York</city>
        </address>
        <phone>
            <number>5551037</number>
        </phone>
    </contacts>
</person>

这是架构:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<xs:schema version="1.0" xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:element name="address" type="address"/>

  <xs:element name="person" type="person"/>

  <xs:element name="phone" type="phone"/>

  <xs:complexType name="person">
    <xs:sequence>
      <xs:element name="first" type="xs:string"/>
      <xs:element name="last" type="xs:string"/>
      <xs:element name="contacts" minOccurs="0">
        <xs:complexType>
          <xs:sequence>
            <xs:choice minOccurs="0" maxOccurs="unbounded">
              <xs:element ref="phone"/>
              <xs:element ref="address"/>
            </xs:choice>
          </xs:sequence>
        </xs:complexType>
      </xs:element>
    </xs:sequence>
  </xs:complexType>

  <xs:complexType name="phone">
    <xs:complexContent>
      <xs:extension base="contactInfomation">
        <xs:sequence>
          <xs:element name="number" type="xs:string"/>
        </xs:sequence>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>

  <xs:complexType name="contactInfomation" abstract="true">
    <xs:sequence/>
  </xs:complexType>

  <xs:complexType name="address">
    <xs:complexContent>
      <xs:extension base="contactInfomation">
        <xs:sequence>
          <xs:element name="country" type="xs:string"/>
          <xs:element name="city" type="xs:string"/>
        </xs:sequence>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
</xs:schema>

文档的@XmlElementRef使用它来替换组和XML的选择.我完全混淆@XmlElementRefs/ @XmlElementRef和@XmlElements/ 的区别是什么@XmlElement.有人可以帮忙吗？

Answer 1

TL; DR

之间的基本Differenece @XmlElement和@XmlElementRef

@XmlElement和之间的区别在于,@XmlElementRef相应的生成元素是否包含本地元素定义或对全局元素定义的引用.

选择和替代团体

XML Schema中的选择实际上是替换组可以完成的超集.因此,为了简化映射,JAXB利用两个映射.

JAXB和Schema Generation

JAXB可以从任何XML Schema生成Java模型,另一方面JAXB不保留有关XML模式的所有元数据.因此,JAXB无法生成每个XML架构.

@XmlElementRefs/ @XmlElementRef和@XmlRootElement

以下是您的模型中的内容.

人

我已经修改了contacts字段上的映射,使得到Address类的映射更加清晰.

@XmlElementWrapper(name = "contacts")
@XmlElementRefs({
    @XmlElementRef(name = "phone", type = Phone.class, required = true),
    @XmlElementRef(name = "ADDRESS", type = Address.class, required = true)
})
private final List<ContactInfomation> contacts = new ArrayList<>();

电话

使用@XmlElementRef您指定的信息进行映射时,需要与由@XmlRootElementor 提供的全局元素定义相对应@XmlElementDecl(请参阅:http://blog.bdoughan.com/2012/07/jaxb-and-root-elements.html).默认情况下,Person类的根元素为person.

@XmlRootElement
public class Person {

地址

我使用了@XmlRootElement注释覆盖了默认名称Address class.

@XmlRootElement(name="ADDRESS")
public class Address extends ContactInfomation {

生成的XML架构

这是生成的架构.我们看到结构中的element定义choice利用ref引用现有元素而不是定义局部元素.

  <xs:element name="contacts" minOccurs="0">
    <xs:complexType>
      <xs:sequence>
        <xs:choice minOccurs="0" maxOccurs="unbounded">
          <xs:element ref="phone"/>
          <xs:element ref="ADDRESS"/>
        </xs:choice>
      </xs:sequence>
    </xs:complexType>
  </xs:element>

@XmlElements/@XmlElement

我已经更改了您contacts要使用的字段上的映射@XmlElements.

人

@XmlElementWrapper(name = "contacts")
@XmlElements({
    @XmlElement(name = "phone-number", type = Phone.class, required = true),
    @XmlElement(name = "home-address", type = Address.class, required = true)
})
private final List<ContactInfomation> contacts = new ArrayList<>();

电话

所有引用的类都不需要注释@XmlRootElement(或具有相应的@XmlElementDecl注释.

public class Phone extends ContactInfomation {

地址

如果他的类确实有@XmlRootElement注释,则不需要匹配@XmlElement注释@XmlElements.

@XmlRootElement(name="ADDRESS")
public class Address extends ContactInfomation {

生成的XML架构

这是生成的架构.我们看到,element在中定义choice的结构现在被定义为本地元素.

  <xs:element name="contacts" minOccurs="0">
    <xs:complexType>
      <xs:sequence>
        <xs:choice maxOccurs="unbounded">
          <xs:element name="phone-number" type="phone"/>
          <xs:element name="home-address" type="address"/>
        </xs:choice>
      </xs:sequence>
    </xs:complexType>
  </xs:element>