在JAXB中解组期间忽略未定义的元素引用

Question

我目前正在从事一个使用CXF框架请求web服务的项目。

由于某些原因，我开始收到无效的XML SOAP（缺少引用了ID的元素）响应，导致在解组到POJO实例期间抛出异常。

示例：

XML摘录，其中属性ref引用标识符为Person1的元素，该元素在XML中不存在。

<ext:Applicant s:ref="Person1"/>

其中ref是XSD模式中的IDREF类型

<attribute name="ref" type="IDREF"/>

JAXB引发的异常

javax.xml.ws.soap.SOAPFaultException: Unmarshalling Error: Undefined ID "Person1". ] with root cause
javax.xml.bind.UnmarshalException: Undefined ID "Person1".
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.handleEvent(UnmarshallingContext.java:744) ~[jaxb-impl-2.3.1.jar!/:2.3.1]
    at com.sun.xml.bind.v2.runtime.unmarshaller.UnmarshallingContext.errorUnresolvedIDREF(UnmarshallingContext.java:795) ~[jaxb-impl-2.3.1.jar!/:2.3.1]
    at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor$IDREFTransducedAccessorImpl$1.run(TransducedAccessor.java:330) ~[jaxb-impl-2.3.1.jar!/:2.3.1]
    at...

有没有一种方法可以让JAXB忽略缺失的引用，并且在不引发异常的情况下取消对传入XML响应的处理？

Answer 1

可能的解决方案是为XMLEventReader创建一个装饰器，它将过滤掉IDREF属性（或其他属性，如果需要）：

public class IdRefFilteringReader implements XMLEventReader {

    /**
     * QName of the attribute to be removed
     */
    private final static QName QNAME = new QName("http://www.w3.org/2001/XMLSchema", "ref");
    
    /**
     * Delegate XML event reader
     */
    private final XMLEventReader delegate;

    /**
     * XML event factory
     */
    private final XMLEventFactory eventFactory = XMLEventFactory.newInstance();

    /**
     * Constructor injects delegate
     */
    public IdRefFilteringReader(XMLEventReader delegate) {
        this.delegate = delegate;
    }

    /**
     * Remove attributes with matching QName
     */
    @Override
    public XMLEvent nextEvent() throws XMLStreamException {
        XMLEvent event = delegate.nextEvent();
        if (event.isStartElement()) {
            StartElement startElement = event.asStartElement();
            Attribute attr = startElement.getAttributeByName(QNAME);
            // if attribute is present, create new XMLEvent with same
            // prefix, namespace, name and other attributes except one
            // which should be removed
            if(attr != null) {
                String prefix = startElement.getName().getPrefix();
                String uri = startElement.getName().getNamespaceURI();
                String localname = startElement.getName().getLocalPart();
                List<Attribute> attributes = new ArrayList<>();
                startElement.getAttributes().forEachRemaining(a -> {
                    if(!a.getName().equals(attr.getName())) {
                        attributes.add(a);
                    }
                });
                return eventFactory.createStartElement(
                        prefix, 
                        uri, 
                        localname, 
                        attributes.iterator(),
                        startElement.getNamespaces()
                );
            }
        }
        return event;
    }

    @Override
    public boolean hasNext() {
        return delegate.hasNext();
    }

    @Override
    public XMLEvent peek() throws XMLStreamException {
        return delegate.peek();
    }

    @Override
    public String getElementText() throws XMLStreamException {
        return delegate.getElementText();
    }

    @Override
    public XMLEvent nextTag() throws XMLStreamException {
        return delegate.nextTag();
    }

    @Override
    public Object getProperty(String name) throws IllegalArgumentException {
        return delegate.getProperty(name);
    }

    @Override
    public void close() throws XMLStreamException {
        delegate.close();
    }

    @Override
    public Object next() {
        return delegate.next();
    }

}

要使用此读取器，需要将其传递给解组器实例，例如：

    // create unmarshaller
    JAXBContext ctx = JAXBContext.newInstance(Applicant.class);
    Unmarshaller unmarshaller = ctx.createUnmarshaller();
    
    // create regular XML event reader and filtered XML event reader
    XMLInputFactory xif = XMLInputFactory.newInstance();
    XMLEventReader reader = xif.createXMLEventReader(new StreamSource(new StringReader(xml))); 
    XMLEventReader filteringReader = new IdRefFilteringReader(reader);
    
    // unmarshall XML using filtering reader
    Applicant applicant = unmarshaller.unmarshal(filteringReader, Applicant.class);

Answer 2

在请求中没有提供XML对象以更具体地讨论。有一个方便的解决方案可以为JAX-B对象创建CustomAdapter，以确定如何列表和散集对象。

例如，可以实现以下CustomAdapter：

public static class CustomAdapter extends XmlAdapter<Object, Person1> {

    @Override
    public Object marshal(Person1 value) {
        // your implementation to marshal
    }

    @Override
    public Person1 unmarshal(Object value) {
        // your implementation to unmarshal
    }
}

XmlAdapter位于XmlAdapter包javax.xml.bind.annotation.adapters.。

如果您将Person1用作其他对象（组合）中的字段，则可以使用@XmlJavaTypeAdapter对其进行注释，如下所示：

  @XmlJavaTypeAdapter(CustomAdapter.class)
  private Person1 person1;

如果有帮助，请告诉我。