用于任意XML的JAXB @XmlAdapter

Question

我有一个org.w3c.dom.Element我正在从我XmlAdapter的自定义返回@XmlElement,我想将它作为任意XML包含在JAXB对象中(我知道我必须手工制作XSD).然而,JAXB抱怨道

org.w3c.dom.Element is an interface, and JAXB can't handle interfaces.

显然,w3c XML类型不支持Java类型,这是一种耻辱.但除此之外,当我使用javax.xml.transform.Result显然支持时,我得到相同的错误.

如何在JAXB中包含任意XML元素作为元素？

注意:根据https://forums.oracle.com/thread/1668210我也试过了

MessageFactory factory = MessageFactory.newInstance();
message = factory.createMessage();          
SOAPElement element = message.getSOAPBody().addDocument(doc);

但这也给出了同样的错误.

Answer 1

TL; DR

只要将值类型指定为(不)XmlAdapter,就可以将域对象转换为实例.org.w3c.dom.ElementObjectElement

以下是一个完整的例子.

XmlAdapter

类型的字段/属性java.lang.Object将未知内容保留为DOM节点.您可以通过在XmlAdapteras中指定值类型来在用例中利用它Object.您需要确保从marshal方法返回的根元素与@XmlElement注释定义的字段/属性匹配.

import javax.xml.bind.annotation.adapters.XmlAdapter;
import javax.xml.parsers.*;
import org.w3c.dom.*;

public class BarAdapter extends XmlAdapter<Object, Bar>{

    private DocumentBuilder documentBuilder;

    public BarAdapter() {
        try {
            DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
            documentBuilder = dbf.newDocumentBuilder();
        } catch(Exception e) {
            // TODO - Handle Exception
        }
    }

    @Override
    public Bar unmarshal(Object v) throws Exception {
        Bar bar = new Bar();
        Element element = (Element) v;
        bar.value = element.getTextContent();
        return bar;
    }

    @Override
    public Object marshal(Bar v) throws Exception {
        Document document = documentBuilder.newDocument();
        Element root = document.createElement("bar");
        root.setTextContent(v.value);
        return root;
    }

}

Java模型

富

该@XmlJavaTypeAdapter注释被用于引用XmlAdapter.

import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Foo {

    @XmlJavaTypeAdapter(BarAdapter.class)
    private Bar bar;

}

酒吧

import javax.xml.bind.annotation.*;

@XmlAccessorType(XmlAccessType.FIELD)
public class Bar {

    String value;

}

演示代码

演示

由于创建DocumentBuilderFactory需要付出代价,因此我们可以通过在Marshaller上设置实例来利用JAXB处理XmlAdapter的有状态实例的能力.

import java.io.File;
import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Foo.class);

        Unmarshaller unmarshaller = jc.createUnmarshaller();
        File xml = new File("src/forum18272059/input.xml");
        Foo foo = (Foo) unmarshaller.unmarshal(xml);

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setAdapter(new BarAdapter());
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(foo, System.out);
    }

}

input.xml中/输出

<?xml version="1.0" encoding="UTF-8"?>
<foo>
    <bar>Hello World</bar>
</foo>