使用jaxb进行marshelling时使用派生类

Question

我有一个具有公共基类的对象列表,我试图使用jaxb将其序列化为XML.我希望在编组时使用派生类的注释,但是我很难到达那里.

import java.util.Arrays;
import java.util.List;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.JAXBException;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.XmlRootElement;


public class Runner {
    @XmlRootElement(name="base")
    public static abstract class Base {
        public int baseValue;

        public Base() {
            this.baseValue = 0;
        }
    }

    @XmlRootElement(name="derived")
    public static class Derived extends Base {
        public int derivedValue;

        public Derived() {
            super();
            this.derivedValue = 1;
        }
    }

    @XmlRootElement(name="derived2")
    public static class Derived2 extends Base {
        public int derivedValue;

        public Derived() {
            super();
            this.derivedValue = 1;
        }
    }

    @XmlRootElement(name="base_list")
    public static class BaseList {
        public List<Base> baseList;
    }

    public static void main(String[] args) throws JAXBException {
        BaseList baseList = new BaseList();
        baseList.baseList = Arrays.asList((Base) new Derived(), (Base) new Derived());

        JAXBContext jaxbContext = JAXBContext.newInstance(BaseList.class);

        Marshaller marshaller = jaxbContext.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);
        marshaller.marshal(baseList, System.out);

    }
}

我想要:

<base_list>
    <derived>
        <baseValue>0</baseValue>
        <derivedValue>1</derivedValue>
    </derived>
    <derived2>
        <baseValue>0</baseValue>
        <derivedValue>1</derivedValue>
    </derived2>
</base_list>

但是,上面的代码给出了:

<base_list>
    <baseList>
        <baseValue>0</baseValue>
    </baseList>
    <baseList>
        <baseValue>0</baseValue>
    </baseList>
</base_list>

有没有办法强迫它使用派生类？在实际情况中,我事先并不知道可能来自Base的类.

请注意,我只需要编组,而不是解组数据.

Answer 1

您可以使用@XmlElementRef注释来处理此用例。 @XmlElementRef对应于 XML 模式中替换组的概念。

举个例子：

• http://bdoughan.blogspot.com/2010/11/jaxb-and-inheritance-using-substitution.html