我正在尝试使用 JAXB (2.1.12) 编码一个具有 DataHandler 字段的对象。对于流式支持，DataHandler 使用@XmlAttachmentRef 注释。通过 Web 服务(JBoss 上的 Metro)进行序列化和流式传输工作正常，但使用 JAXB 进行简单编码却不行。

这是一个精简的例子:

public class DataHandlerAttachmentSerialization {

    @XmlRootElement
    static class RootObject {
        @XmlElement
        @XmlAttachmentRef // Works without this, but required for streaming 
        DataHandler dataHandler = new DataHandler(
                new com.sun.xml.ws.util.ByteArrayDataSource(
                " ".getBytes(), "application/octet-stream"));
    }

    @Test
    public void test() throws JAXBException {
        JAXBContext context = JAXBContext.newInstance(RootObject.class);
        Marshaller marshaller = context.createMarshaller();
        StringWriter writer = new StringWriter();
        marshaller.marshal(new RootObject(), writer);
        Assert.assertNotNull(writer.toString());
    }
}

运行此测试会产生以下堆栈跟踪:

javax.xml.bind.MarshalException
 - with linked exception:
[com.sun.xml.bind.api.AccessorException: java.lang.NullPointerException]
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:318)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:244)
    at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:96)
    ...
Caused by: com.sun.xml.bind.api.AccessorException: java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:246)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.reportError(XMLSerializer.java:261)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:335)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsSoleContent(XMLSerializer.java:593)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:320)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:494)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:315)
    ... 25 more
Caused by: com.sun.xml.bind.api.AccessorException: java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.reflect.AdaptedAccessor.get(AdaptedAccessor.java:74)
    at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor$CompositeTransducedAccessorImpl.writeLeafElement(TransducedAccessor.java:250)
    at com.sun.xml.bind.v2.runtime.property.SingleElementLeafProperty.serializeBody(SingleElementLeafProperty.java:98)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:332)
    ... 29 more
Caused by: java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.SwaRefAdapter.marshal(SwaRefAdapter.java:80)
    at com.sun.xml.bind.v2.runtime.SwaRefAdapter.marshal(SwaRefAdapter.java:65)
    at com.sun.xml.bind.v2.runtime.reflect.AdaptedAccessor.get(AdaptedAccessor.java:72)
    ... 32 more

SwaRefAdapter 中的第 80 行是 return am.addSwaRefAttachment(data); 并且 am 被分配了 AttachmentMarshaller am = XMLSerializer。 getInstance().attachmentMarshaller; 如果 @XmlAttachmentRef 存在，那么此时 attachmentMarshaller 似乎为空。

我是否需要进行不同的设置，或者以不同的方式使用 JAXB API 来处理附件？

最佳答案

在 JAX-WS 环境之外使用 JAXB 时，JAXB 实现应该默认内联 XML 文档中的二进制内容作为 base64Binary。

这似乎是 JAXB(JDK/JRE 中包含的 RI)的 Metro 实现中的错误。如果您使用另一个 JAXB 实现，例如 EclipseLink JAXB (MOXy) ，这将正常工作。要使用 EclipseLink MOXy，请将 eclipselink.jar ( available here ) 添加到您的类路径，并在以下内容时将 jaxb.properties 文件添加到您的模型类中:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

JAX-WS 注册 AttachmentMarshallers 和 AttachmentUnmarshallers 来处理 JAXB 模型中的二进制内容。如果需要，您可以在独立使用 JAXB 时指定自己的。

http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/javax/xml/bind/attachment/AttachmentMarshaller.html

关于java - 如何使用 JAXB 编码注释为 @XmlAttachmentRef 的 DataHandler？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/1667869/