当JAXB(JSR-222)实现无法仅根据值确定要执行的操作时,JAXBElement
将作为模型的一部分生成。在您的示例中,您可能有一个元素如下:
<xsd:element
name="includeAllSubaccounts" type="xsd:boolean" nillable="true" minOccurs="0"/>
生成的属性不能是
boolean
,因为
boolean
无法表示
null
。您可以将属性设置为
Boolean
,但这样如何区分缺少元素和设置了
xsi:nil
的元素。这就是 JAXBElement 发挥作用的地方。请参见下面的完整示例:
Foo
package forum12713373;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.*;
@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {
@XmlElementRef(name="absent")
JAXBElement<Boolean> absent;
@XmlElementRef(name="setToNull")
JAXBElement<Boolean> setToNull;
@XmlElementRef(name="setToValue")
JAXBElement<Boolean> setToValue;
}
ObjectFactory
package forum12713373;
import javax.xml.bind.JAXBElement;
import javax.xml.bind.annotation.*;
import javax.xml.namespace.QName;
@XmlRegistry
public class ObjectFactory {
@XmlElementDecl(name="absent")
public JAXBElement<Boolean> createAbsent(Boolean value) {
return new JAXBElement(new QName("absent"), Boolean.class, value);
}
@XmlElementDecl(name="setToNull")
public JAXBElement<Boolean> createSetToNull(Boolean value) {
return new JAXBElement(new QName("setToNull"), Boolean.class, value);
}
@XmlElementDecl(name="setToValue")
public JAXBElement<Boolean> createSetToValue(Boolean value) {
return new JAXBElement(new QName("setToValue"), Boolean.class, value);
}
}
演示
package forum12713373;
import javax.xml.bind.*;
public class Demo {
public static void main(String[] args) throws Exception {
JAXBContext jc = JAXBContext.newInstance(Foo.class);
ObjectFactory objectFactory = new ObjectFactory();
Foo foo = new Foo();
foo.absent = null;
foo.setToNull = objectFactory.createSetToNull(null);
foo.setToValue = objectFactory.createSetToValue(false);
Marshaller marshaller = jc.createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
marshaller.marshal(foo, System.out);
}
}
输出
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<foo>
<setToNull xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true"/>
<setToValue>false</setToValue>
</foo>
JAXBElement
,为什么你要尝试传递一个布尔值true
呢? - NullUserExceptionJAXBElement<Boolean> jaxtrue = new JaxBElement(qname, Boolean.TYPE, Boolean.TRUE);
,并传递它。 - NullUserException