java - 如何使用 JAXB 使类字段成为标签名称？

Question

我正在使用 Java 和 JAXB 进行 XML 处理。

我有以下类(class):

public class Characteristic {

    private String characteristic;
    private String value;

    @XmlAttribute
    public String getCharacteristic() {
        return characteristic;
    }

    public void setCharacteristic(String characteristic) {
        this.characteristic = characteristic;
    }

    @XmlValue
    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

public static void main(String[] args) {
    Characteristic c = new Characteristic();
    c.setCharacteristic("store_capacity");
    c.setValue(40);
    Characteristic c2 = new Characteristic();
    c2.setCharacteristic("number_of_doors");
    c2.setValue(4);
}

这是我得到的结果:

<characteristics characteristic="store_capacity">40</characteristics>
<characteristics characteristic="number_of_doors">4</characteristics>

我想得到如下结果:

<store_capacity>40</store_capacity>
<number_of_doors>4</number_of_doors>

我怎样才能做到这一点？

Answer 1

您可以使用 @XmlElementRef 的组合和 JAXBElement生成动态元素名称。

思路是:

• 制作Characteristic JAXBElement 的子类并覆盖 getName()方法返回基于 characteristic 的名称属性(property)。
• 注释 characteristics与 @XmlElementRef .
• 提供 @XmlRegistry ( ObjectFactory ) 与 @XmlElementDecl(name = "characteristic") .

下面是一个working test .

测试本身(没什么特别的):

@Test
public void marshallsDynamicElementName() throws JAXBException {
    JAXBContext context = JAXBContext.newInstance(ObjectFactory.class);
    final Characteristics characteristics = new Characteristics();
    final Characteristic characteristic = new Characteristic(
            "store_capacity", "40");
    characteristics.getCharacteristics().add(characteristic);
    context.createMarshaller().marshal(characteristics, System.out);
}

产生:

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<characteristics><store_capacity>40</store_capacity></characteristics>

让我们从 characteristics 开始根元素类。它有一个 characteristics用 @XmlElementRef 注释的属性.这意味着内容应该是JAXBElement。 s 或 @XmlRootElement - 带注释的类实例。

@XmlRootElement(name = "characteristics")
public class Characteristics {

    private final List<Characteristic> characteristics = new LinkedList<Characteristic>();

    @XmlElementRef(name = "characteristic")
    public List<Characteristic> getCharacteristics() {
        return characteristics;
    }

}

为了让它工作，你还需要一个 ObjectFactory或者用 @XmlRegistry 注释的东西有相应的 @XmlElementDecl :

@XmlRegistry
public class ObjectFactory {

    @XmlElementDecl(name = "characteristic")
    public JAXBElement<String> createCharacteristic(String value) {
        return new Characteristic(value);
    }

}

回想一下，characteristics属性必须包含 @XmlRootElement - 带注释的类实例或 JAXBElement秒。 @XmlRootElement不适合，因为它是静态的。但是JAXBElement是动态的。您可以子类化 JAXBElement并覆盖 getName()方法:

public class Characteristic extends JAXBElement<String> {
    private static final long serialVersionUID = 1L;
    public static final QName NAME = new QName("characteristic");

    public Characteristic(String value) {
        super(NAME, String.class, value);
    }

    public Characteristic(String characteristic, String value) {
        super(NAME, String.class, value);
        this.characteristic = characteristic;
    }

    @Override
    public QName getName() {
        final String characteristic = getCharacteristic();
        if (characteristic != null) {
            return new QName(characteristic);
        }
        return super.getName();
    }

    private String characteristic;

    @XmlTransient
    public String getCharacteristic() {
        return characteristic;
    }

    public void setCharacteristic(String characteristic) {
        this.characteristic = characteristic;
    }
}

在这种情况下，我已经覆盖了 getName()动态确定元素名称的方法。如果characteristic属性已设置，其值将用作名称，否则该方法选择默认值 characteristic元素。

测试代码为available on GitHub .