如何使用xstream將Hashmap映射到XML中的鍵值屬性

Question

我有以下實體：

@XStreamAlias("entity")
public class MapTestEntity {

    @XStreamAsAttribute
    public Map<String, String> myMap = new HashMap<>();

    @XStreamAsAttribute
    public String myText;
}

我在xstream中使用它：

MapTestEntity e = new MapTestEntity();
e.myText = "Foo";
e.myMap.put("firstname", "homer");
e.myMap.put("lastname", "simpson");

XStream xstream = new XStream(new PureJavaReflectionProvider());
xstream.processAnnotations(MapTestEntity.class);
System.out.println(xstream.toXML(e));

並獲取以下xml：

<entity myText="Foo">
  <myMap>
    <entry>
      <string>lastname</string>
      <string>simpson</string>
    </entry>
    <entry>
      <string>firstname</string>
      <string>homer</string>
    </entry>
  </myMap>
</entity>

但我需要將HashMap映射到xml中的屬性，如：

<entity myText="Foo" lastname="simpson" firstname="homer" />

我怎么能用XStream做到這一點？ 我可以使用自定義轉換器或映射器或類似的東西嗎？ TIA！

（當然我的代碼需要確保在xml屬性中沒有重復。）

Answer 1

NamedMapConverter可以實現這一點。 看看http://x-stream.github.io/javadoc/com/thoughtworks/xstream/converters/extended/NamedMapConverter.html

第三個例子准確地說明了你想要的：

    new NamedMapConverter(xstream.getMapper(), "entry", "key", String.class, "value", Integer.class, true, true, xstream.getConverterLookup());

創建此xml輸出：

    <map>
        <entry key="keyValue" value="0"/>
    </map>

Answer 2

我寫了一個自己的轉換器：

public class MapToAttributesConverter implements Converter {

    public MapToAttributesConverter() {
    }

    @Override
    public boolean canConvert(Class type) {
        return Map.class.isAssignableFrom(type);
    }

    @Override
    public void marshal(Object source, HierarchicalStreamWriter writer, MarshallingContext context) {
        Map<String, String> map = (Map<String, String>) source;
        for (Map.Entry<String, String> entry : map.entrySet()) {
            writer.addAttribute(entry.getKey(), entry.getValue().toString());
        }
    }

    @Override
    public Object unmarshal(HierarchicalStreamReader reader, UnmarshallingContext context) {
        Map<String, String> map = new HashMap<String, String>();
        for (int i = 0; i < reader.getAttributeCount(); i++) {
            String key = reader.getAttributeName(i);
            String value = reader.getAttribute(key);
            map.put(key, value);
        }
        return map;
    }
}