Java HTML/XML - 如何如果设置了另一个可选属性，请设置可选属性

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.XmlAccessType;
import javax.xml.bind.annotation.XmlAccessorType;
import javax.xml.bind.annotation.XmlAttribute;
import javax.xml.bind.annotation.XmlRootElement;

public class Main {

  public static void main(String[] args) throws Exception {
    JAXBContext jc = JAXBContext.newInstance(Field.class);
    Marshaller marshaller = jc.createMarshaller();
    marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);

    Field field = new Field();
    field.name = "myField";
    marshaller.marshal(field, System.out);

    field.status = "citizen";
    field.country = "England";
    marshaller.marshal(field, System.out);

    field.status = null;
    marshaller.marshal(field, System.out);
  }

  @XmlRootElement
  @XmlAccessorType(XmlAccessType.FIELD)
  public static class Field {

    @XmlAttribute
    String name;

    @XmlAttribute
    String status;

    @XmlAttribute
    String country;

    private void beforeMarshal(Marshaller marshaller) {
      if (country != null && status == null) {
        throw new RuntimeException("country was set but status was not");
      }
    }

  }

}