optional JAXB xml attribute while marshalling

问题

When I marshal java object using JAXB I am getting below xml element

<error line="12" column="" message="test" />

But I want xml as below

<error line="12" message="test" />

If column value is empty then I need to get the xml as shown above otherwise I need to get the column attribute in the element.

Is there any way to get it?

回答1:

An attribute will only be marshalled out with an empty String value if the corresponding field/property contains a empty String value. If the value is null the attribute will not be marshalled.

Root

package forum13218462;

import javax.xml.bind.annotation.*;

@XmlRootElement
public class Root {

    @XmlAttribute
    String attributeNull;

    @XmlAttribute
    String attributeEmpty;

    @XmlAttribute(required=true)
    String attributeNullRequired;

}

Demo

package forum13218462;

import javax.xml.bind.*;

public class Demo {

    public static void main(String[] args) throws Exception {
        JAXBContext jc = JAXBContext.newInstance(Root.class);

        Root root = new Root();
        root.attributeNull = null;
        root.attributeEmpty = "";
        root.attributeNullRequired = null;

        Marshaller marshaller = jc.createMarshaller();
        marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
        marshaller.marshal(root, System.out);
    }

}

Output

<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<root attributeEmpty=""/>

来源：https://stackoverflow.com/questions/13218462/optional-jaxb-xml-attribute-while-marshalling