JAXB - 如何根据XML值设置XML元素的xsi：类型？

I have to generate a xml element that can have as value any "primitive type" (xsd:string, xsd:boolean, etc). Examples:

我必须生成一个xml元素,它可以具有任何“基本类型”(xsd:string,xsd:boolean等)作为值。例子:

<field xsi:type="xsd:string" name="aString">String Value</field>
<field xsi:type="xsd:date" name="aDate">2011-10-21</field>
...

So, I tried two implementations:

所以,我尝试了两个实现:

public class Field {
    @XmlAttribute
    private String name;

    @XmlValue
    Object value;
}

and ...

public class Field<T> {
    @XmlAttribute
    private String name;

    @XmlValue
    T value;
}

I'm testing this with:

我正在测试这个:

Marshaller marshaller = JAXBContext.newInstance(Field.class).createMarshaller();
marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
marshaller.setProperty("com.sun.xml.bind.xmlDeclaration", Boolean.FALSE);

Field field = new Field();
field.name = "name";
field.value = "value";

ByteArrayOutputStream stream = new ByteArrayOutputStream();
marshaller.marshal(field, new PrintWriter(stream));
System.out.println(stream);

But I'm getting this NullPointerException when I try to instantiate the JAXBContext.

但是当我尝试实例化JAXBContext时,我得到了这个NullPointerException。

java.lang.NullPointerException
at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor.get(TransducedAccessor.java:165)
at com.sun.xml.bind.v2.runtime.property.ValueProperty.<init>(ValueProperty.java:77)
at com.sun.xml.bind.v2.runtime.property.PropertyFactory.create(PropertyFactory.java:106)
at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.<init>(ClassBeanInfoImpl.java:179)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.getOrCreate(JAXBContextImpl.java:515)
at com.sun.xml.bind.v2.runtime.JAXBContextImpl.<init>(JAXBContextImpl.java:330)
at

The idea is allow schema validation for the field element (It is define in a schema must its type will be set in each instance). So, even is this a Bug (or not) ... how JAXB will put the correct xsi:type to this field instance? I'm missing a concept here?

这个想法是允许字段元素的模式验证(它在模式中定义必须在每个实例中设置其类型)。所以,即使这是一个Bug(或不是)...... JAXB如何将正确的xsi:type放到这个字段实例中?我在这里错过了一个概念?

I know that maybe the problem is the usage of the @XmlValue because of this restrictions (from the javadoc):

我知道问题可能是@XmlValue的使用,因为这个限制(来自javadoc):

At most one field or property can be annotated with the @XmlValue annotation.

最多可以使用@XmlValue批注对一个字段或属性进行批注。

@XmlValue can be used with the following annotations: XmlList. However this is redundant since XmlList maps a type to a simple schema type that derives by list just as XmlValue would.

@XmlValue可以与以下注释一起使用:XmlList。然而,这是多余的,因为XmlList将类型映射到一个简单的模式类型,该模式类型按照XmlValue的方式按列表派生。

If the type of the field or property is a collection type, then the collection item type must map to a simple schema type.

如果字段或属性的类型是集合类型,则集合项类型必须映射到简单的模式类型。

If the type of the field or property is not a collection type, then the type must map to a XML Schema simple type.

如果字段或属性的类型不是集合类型,则该类型必须映射到XML Schema简单类型。

... because an Object or a generic T is not necessarily a XML Schema simple type, this approach seems not to be the correct one ...

...因为Object或泛型T不一定是XML Schema简单类型,这种方法似乎不是正确的...

Thanks in advance ...

提前致谢 ...

1 个解决方案

#1

I have confirmed the issue you are seeing in both the reference and EclipseLink JAXB (MOXy) implementations of JAXB. The problem you are seeing is due to use of @XmlValue. If the value property was mapped as an @XmlElement you would see the xsi:type attribute appear as expected.

我已经确认了您在JAXB的引用和EclipseLink JAXB(MOXy)实现中看到的问题。您看到的问题是由于使用了@XmlValue。如果value属性被映射为@XmlElement,您会看到xsi:type属性按预期显示。

I have entered the following bug to track this issue in EclipseLink JAXB (MOXy):

我在EclipseLink JAXB(MOXy)中输入了以下错误来跟踪此问题:

https://bugs.eclipse.org/361689

Depending upon what your domain model looks like you may be interested in the @XmlPath extension from EclipseLink JAXB (MOXy):

根据您的域模型的样子,您可能对EclipseLink JAXB(MOXy)中的@XmlPath扩展感兴趣:

http://blog.bdoughan.com/2011/03/map-to-element-based-on-attribute-value.html

UPDATE

This issue has now been fixed in the EclipseLink 2.3.3 and EclipseLink 2.4.0. The fix is available in these streams starting March 17, 2012 and can be obtained from:

此问题现已在EclipseLink 2.3.3和EclipseLink 2.4.0中得到修复。从2012年3月17日开始,可以在这些流中使用此修复程序,可以从以下位置获取:

http://www.eclipse.org/eclipselink/downloads/nightly.php

#1