How to ignore a field from binding to XML with JAX

问题:

I have a simple class that looks like this

    import nl.hu.pf.coproco.model.Observeable;

    @XmlRootElement (name = "Purpose")
    @XmlAccessorType (XmlAccessType.FIELD)
    public class Purpose implements Observeable{
        private String name;
        private ArrayList<Observer> observers;

        @XmlElement (name = "subPurpose")
        private ArrayList<Purpose> subPurposes;

        //methods
    }

But Observable is an interface so I get an exception because JAXB can'ty handle interfaces. I tried figuring out how to ignore the field with the ArrayList<Observer> so it wont be exported to xml.

I tried using the @XmlTransient annotation but the I get the following eception javax.xml.bind.UnmarshalException: unexpected element (uri:"", local:"purpose"). Expected elements are <{}Purpose>

This happens when Unmarshalling but I want to Marshall that class too

Sample xml

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<purpose>
    <name>All Purposes</name>
    <subPurpose>
        <name>Creational</name>
    </subPurpose>
    <subPurpose>
        <name>Structural</name>
    </subPurpose>
    <subPurpose>
        <name>Behavioral</name>
        <subPurpose>
            <name>Behavioral 1</name>
        </subPurpose>
        <subPurpose>
            <name>Behavioral 2</name>
        </subPurpose>
    </subPurpose>
</purpose>

The interface Observable looks like this:

public interface Observeable {
    public void registerObserver(Observer o);
    public void removeObserver(Observer o);
    public void notifyObservers(Object o, String arg);
}

回答1:

Your xml contains purpose not Purpose so change @XmlRootElement(name = "Purpose") to

@XmlRootElement(name = "purpose")

And add @XmlTransient on observers like this

@XmlTransient
private ArrayList<Observer> observers;