JAXB默认属性值

Question

I'm using JAXB annotations to generate xsd schema from my classes.

Annotation @XmlElement with parameter defaultValue sets default value for element. Is it possible to set default value for @XmlAttribute?

PS I checked that xsd syntax allow default values for attributes

Answer 1

Might wanna check this: Does JAXB support default schema values?

To be honest, I don't have a clue why there isn't an attribute default option in standard JAXB.

Answer 2

当从xsd生成类并在其中定义具有默认值的属性时，jaxb将生成一个if子句，在其中将检查null值，如果是，则将返回默认值。

Answer 3

For XML attributes default value goes inside getter method.

for Example,

customer.xsd

<?xml version="1.0" encoding="UTF-8"?>
<schema xmlns="http://www.w3.org/2001/XMLSchema">
    <element name="Customer">
        <complexType>
            <sequence>
                <element name="element" type="string" maxOccurs="1" minOccurs="0" default="defaultElementName"></element>
            </sequence>
            <attribute name="attribute" type="string" default="defaultAttributeValue"></attribute>
        </complexType>
    </element>
</schema>

It will generate class like below.

@XmlRootElement(name = "Customer")
public class Customer {

    @XmlElement(required = true, defaultValue = "defaultElementName")
    protected String element;
    @XmlAttribute(name = "attribute")
    protected String attribute;

    ......

    public String getAttribute() {
        //here the default value is set.
        if (attribute == null) {
            return "defaultAttributeValue";
        } else {
            return attribute;
        }
    }

Created Sample XML to read

<?xml version="1.0" encoding="UTF-8" standalone="yes"?><Customer><element/></Customer>

when we write logic to marshall in our main class.

File file = new File("...src/com/testdefault/xsd/CustomerRead.xml");
            JAXBContext jaxbContext = JAXBContext.newInstance(Customer.class);

            Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
            Customer customer = (Customer) jaxbUnmarshaller.unmarshal(file);
            System.out.println(customer.getElement());
            System.out.println(customer.getAttribute());

It will print, in console. defaultElementName defaultAttributeValue

PS -: to get default value of elements you need to have a blank copy of element into xml which is being marshalled.