JAXB的XmlAttribute注解

• JAXB的XmlAttribute注解，将一个JavaBean属性映射到一个XML属性。

例如，下面的Java代码，将属性currency映射到了XML的属性currency：

package com.thb;

import jakarta.xml.bind.annotation.XmlAttribute;
import jakarta.xml.bind.annotation.XmlRootElement;
import jakarta.xml.bind.annotation.XmlType;
import jakarta.xml.bind.annotation.XmlValue;

@XmlRootElement
@XmlType(name = "", propOrder = {"value"})
public class Price {

    @XmlValue
    public String value;

    @XmlAttribute(name = "currency")
    public String currency;
}

生成的XML Schema：

<?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="price">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="currency" type="xs:string"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>
</xs:schema>

• XmlAttribute的required属性指定被注解的属性是否必选。
  例如下面代码，Java属性currency用@XmlAttribute(name = "currency", required = true)注解，指明xml属性currency是必选的：

  package com.thb;

  import jakarta.xml.bind.annotation.XmlAttribute;
  import jakarta.xml.bind.annotation.XmlRootElement;
  import jakarta.xml.bind.annotation.XmlType;
  import jakarta.xml.bind.annotation.XmlValue;

  @XmlRootElement
  @XmlType(name = "", propOrder = {"value"})
  public class Price {

    @XmlValue
    public String value;
  
    @XmlAttribute(name = "currency", required = true)
    public String currency;
  

  }

生成的XML Schema，属性currency中出现了use="required"：

 <?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="price">
    <xs:complexType>
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="currency" type="xs:string" use="required"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>
</xs:schema>