java - 具有特定类型但名称未知的 JAXB 元素

Question

我有根 Xml document (name = "Entity")其中包含一个已知的 Xml element (name = "Header")和另一个名称未知的 Xml 元素，但已知它有一个内部 XmlElement(name="label")

以下是可能的 Xml:

<Entity>
   <Header>this is a header</Header>
   <a>
     <label>this is element A</label>
     <otherElements/>
   </a>
</Entity>

<Entity>
   <Header>this is a different header</Header>
   <b>
     <label>this is some other element of name b</label>
     <others/>
   </b>
</Entity>

这是我的 JAXB 注释类:

@XmlRootElement(name = "Entity")
@XmlAccessorType(XmlAccessType.NONE)
public class Entity {
    @XmlElement(name = "Header")
    private Header header;

    @XmlElements( {
       @XmlElement(name = "a", type=LabelledElement.A.class), 
       @XmlElement(name = "b", type=LabelledElement.B.class)
    } )
    private LabelledElement labelledElement;

    // constructors, getters, setters...
}

@XmlAccessorType(XmlAccessType.NONE)
public abstract class LabelledElement {
     @XmlElement
     private String label;
     @XmlAnyElement
     private List<Element> otherElements;

     public static class A extends LabelledElement {}
     public static class B extends LabelledElement {}
}

这太棒了!但后来我注意到它不仅是 <a>和 <b>

可能是<c> , <asd>甚至<anything> ...

因此列出 XmlElement(name = "xyz", type = LabelledElement.xyz.class)显然不是正确的解决方案。

我只关心Entity#getLabelledElement()#getLabel()不管LabelledElement名字是。

JAXB 甚至可以做到这一点吗？

Answer 1

使用 EclipseLink JAXB 实现 (MOXy)，这应该可以工作:

@XmlRootElement(name = "Entity")
@XmlSeeAlso({LabelledElement.class}) //Might not be necessary
@XmlAccessorType(XmlAccessType.NONE)
public class Entity {
    @XmlElement(name = "Header")
    private Header header;

    @XmlPath("child::*[position() = 2]")
    @XmlJavaTypeAdapter(MapAdapter.class)
    private Map<String,LabelledElement> labelledElementMap;


    public LabelledElement getLabelledElement(){
         return labelledElementMap.values().get(0);
    }
    // constructors, getters, setters...
}

MapAdapter 类:

public class MapAdapter extends XmlAdapter<MapAdapter.AdaptedMap, Map<String, LabelledElement>> {

    public static class AdaptedMap {

        @XmlVariableNode("key")
        List<LabbeledElement> entries = new ArrayList<LabbeledElement>();

    }

    public static class AdaptedEntry {

        @XmlTransient
        public String key;

        @XmlElement
        public LabelledElement value;

    }

    @Override
    public AdaptedMap marshal(Map<String, LabelledElement> map) throws Exception {
        AdaptedMap adaptedMap = new AdaptedMap();
        for(Entry<String, LabelledElement> entry : map.entrySet()) {
            AdaptedEntry adaptedEntry = new AdaptedEntry();
            adaptedEntry.key = entry.getKey();
            adaptedEntry.value = entry.getValue();
            adaptedMap.entries.add(adaptedEntry);
        }
        return adaptedMap;
    }

    @Override
    public Map<String, LabelledElement> unmarshal(AdaptedMap adaptedMap) throws Exception {
        List<AdaptedEntry> adaptedEntries = adaptedMap.entries;
        Map<String, LabelledElement> map = new HashMap<String, LabelledElement>();
        for(AdaptedEntry adaptedEntry : adaptedEntries) {
            map.put(adaptedEntry.key, adaptedEntry.value);
        }
        return map;
    }

}

作为引用，我的解决方案灵感来自 this link .