3

如果设置了可选属性，那么我希望突然需要另一个属性。此外，这意味着只有在设置了前一个属性的情况下才能设置梯形图可选属性。

IE，

名称是必需的

status 是可选的，但如果设置，则还需要指定国家/地区。

只有在给出状态时才设置国家。

<field name="myField" status="citizen" country="England"/>

一个有效的 xml 标记也可以是 status 和 country 为 null 的地方（因此没有解组）：

<field name="myField" />

如果我将可选字段放在他们自己的 xml 标签中可能会更容易？也许是这样的：

<field name="myField">
     <option status="citizen" country="England"/>
</field>

虽然第一种方法可能吗？

4

1 回答 1

2

您可以使用beforeMarshal事件并执行以下操作：

场地

如果您不喜欢beforeMarshal在域类上使用该方法，则可以实现 aMarshaller.Listener并设置在Marshaller（请参阅： http ://docs.oracle.com/javase/6/docs/api/javax/xml/bind/Marshaller .Listener.html）。

package forum13918891;

import javax.xml.bind.Marshaller;
import javax.xml.bind.annotation.*;

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public 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");
        }
    }

}

演示

下面是一些演示代码来证明一切正常。

package forum13918891;

import javax.xml.bind.*;

public class Demo {

    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);
    }

}

输出

下面是运行演示代码的输出。

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<field name="myField"/>
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<field name="myField" status="citizen" country="England"/>
Exception in thread "main" java.lang.IllegalStateException: java.lang.reflect.InvocationTargetException
    at com.sun.xml.bind.v2.runtime.XMLSerializer.fireMarshalEvent(XMLSerializer.java:758)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.fireBeforeMarshalEvents(XMLSerializer.java:743)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:491)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.write(MarshallerImpl.java:315)
    at com.sun.xml.bind.v2.runtime.MarshallerImpl.marshal(MarshallerImpl.java:244)
    at javax.xml.bind.helpers.AbstractMarshallerImpl.marshal(AbstractMarshallerImpl.java:75)
    at forum13918891.Demo.main(Demo.java:21)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.fireMarshalEvent(XMLSerializer.java:755)
    ... 6 more
Caused by: java.lang.RuntimeException: country was set but status was not
    at forum13918891.Field.beforeMarshal(Field.java:21)
    ... 11 more
于 2012-12-21T19:55:24.890 回答