java - Java: Jaxb Interface

Question

Please take a look at the following example. I got the exception that XmlIDREF annotation is not allowed in class Bar. If you use the concrete Class Bar instead of IBar it works perfectly. But i have to use the interface. Is there a solution for this problem?

@XmlRootElement
public class Foo {

    @XmlElement(name = "bar")   
    public List<Bar> bars;

    public String fooProp;
}

public interface IBar { 
    @XmlID
    String getId(); 

    void setId(String id);
}

@XmlRootElement
public class Bar implements IBar {   

    @XmlIDREF
    @XmlAnyElement
    public IBar bar;

    public String barProp;

    private String id;     

    @Override
    @XmlID
    public String getId() {
        return this.id;
    }

    @Override
    public void setId(String id) {
        this.id = id;
    }
}

public static void main(String[] args) throws Exception {
    File file = null;
    file = new File("somewhere");

    try(Writer w = new FileWriter(file)){
        JAXBContext context = JAXBContext.newInstance("jaxbtest");
        Marshaller m = context.createMarshaller();
        m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);

        Foo foo = new Foo();
        foo.fooProp ="FooProperty";

        Bar bar1 = new Bar();           
        bar1.barProp = "BarProperty1";
        bar1.setId("1");

        Bar bar2 = new Bar();           
        bar2.barProp = "BarProperty2";
        bar2.setId("2");

        bar1.bar = bar2;
        bar2.bar = bar1;

        List<Bar> list = new ArrayList<Bar>();
        list.add(bar1);
        list.add(bar2);
        foo.bars = list;        

        m.marshal(foo, w);
    } catch (Exception e) {
        e.printStackTrace();
    }   
}

Answer 1

一种解决方法是使用@XmlElements注释和telljaxb 上下文所有可能的实现IBar：

@XmlIDREF
@XmlElements( @XmlElement( type = Bar.class )/*, @XmlElement( type = AnotherBar.class) */ )
public IBar bar;