java - JAXB 使用 namespace 解码..如何？

Question

假设我的有效 xml 如下所示:

<A xmlns="something">
   <B>4</B>
</A>

我的代码是这样的:

@XmlRootElement(name = "A")
@XmlAccessorType (XmlAccessType.FIELD)
@Getter //from lombok
public class Data{

@XmlElement(name = "B")
private String b;

public Data(String b) {
    this.b = b;
}

public Data() {
}
// Getter/setter generated by lombok.
}

我该如何让它发挥作用？如果我的 xml 标记具有一些关联元素，例如上面的“xmlns”，则 JAXB 解码器会抛出异常。

我是第一次这样做，所以我真的对 JAXB、解码等一无所知。我正在挣扎。 :) 任何帮助都会很好。

编辑 堆栈跟踪:

javax.xml.bind.UnmarshalException: unexpected element (uri:"something", local:"A"). Expected elements are <{}B>,<{}A>
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.handleEvent(UnmarshallingContext.java:726)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:247)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportError(Loader.java:242)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.Loader.reportUnexpectedChildElement(Loader.java:109)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext$DefaultRootLoader.childElement(UnmarshallingContext.java:1131)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext._startElement(UnmarshallingContext.java:556)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.UnmarshallingContext.startElement(UnmarshallingContext.java:538)
at com.sun.xml.internal.bind.v2.runtime.unmarshaller.SAXConnector.startElement(SAXConnector.java:153)
at com.sun.org.apache.xerces.internal.parsers.AbstractSAXParser.startElement(AbstractSAXParser.java:509)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.scanStartElement(XMLNSDocumentScannerImpl.java:374)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl$NSContentDriver.scanRootElementHook(XMLNSDocumentScannerImpl.java:613)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl$FragmentContentDriver.next(XMLDocumentFragmentScannerImpl.java:3132)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl$PrologDriver.next(XMLDocumentScannerImpl.java:852)
at com.sun.org.apache.xerces.internal.impl.XMLDocumentScannerImpl.next(XMLDocumentScannerImpl.java:602)
at com.sun.org.apache.xerces.internal.impl.XMLNSDocumentScannerImpl.next(XMLNSDocumentScannerImpl.java:112)
at   com.sun.org.apache.xerces.internal.impl.XMLDocumentFragmentScannerImpl.scanDocument(XMLDocumentFragmentScannerImpl.java:505)
at ...

Answer 1

来自 XmlRootElement 的来源:

public @interface XmlRootElement {
    /**
     * namespace name of the XML element.
     * <p>
     * If the value is "##default", then the XML namespace name is derived
     * from the package of the class ( {@link XmlSchema} ). If the
     * package is unnamed, then the XML namespace is the default empty
     * namespace.
     */
    String namespace() default "##default";
     // else of file

您还应该记住，此规则也适用于大多数 JAXB 注释，因此您需要指定根元素以及其他元素并显式给出命名空间，如下所示:

@XmlRootElement(namespace="something", name = "A")
@XmlAccessorType (XmlAccessType.FIELD)
@Getter //from lombok
public class Data{
    @XmlElement(namespace="something", name = "B") // <-- mind this
    private String b;

    public Data(String b) {
        this.b = b;
    }

    public Data() {
    }
    // Getter/setter generated by lombok.
}

如果您不这样做，假设您的 Data 位于 org.example 包中，它会期望命名空间 org.example 中的一些元素> 只要您有@XmlSchema(elementFormDefault=QUALIFIED)，否则它将需要默认命名空间中的元素。