What is the difference between using @XmlElement before field and before getter declaration?

Question

I can declare JAXB element in two ways:

@XmlElement
public int x;

or

private int x;

@XmlElement
public int getX(){...}


        

Answer 1

The use of @XMLElement (and similar annotations) before fields or before getters is well explained in this post: http://blog.bdoughan.com/2011/06/using-jaxbs-xmlaccessortype-to.html.

The following annotation before a class determines the XML bindings of fields/getters:

• @XmlAccessorType(XmlAccessType.PUBLIC_MEMBER): public fields, annotated fields and properties
• @XmlAccessorType(XmlAccessType.PROPERTY): annotated fields and properties
• @XmlAccessorType(XmlAccessType.FIELD): fields and annotated properties
• @XmlAccessorType(XmlAccessType.NONE): annotated fields and annotated properties

Answer 2

It relates to the @XmlAccessorType annotation.

• XmlAccessType.PROPERTY : Fields are bound to XML only when they are explicitly annotated by some of the JAXB annotations.

• XmlAccessType.FIELD: Getter/setter pairs are bound to XML only when they are explicitly annotated by some of the JAXB annotations

Update to explain based on comment:

Let's consider a simple xml that looks like this:

<root>
    <value>someValue</value>
</root>

And we have a class:

@XmlRootElement(name = "root")
//@XmlAccessorType(XmlAccessType.PROPERTY)
@XmlAccessorType(XmlAccessType.FIELD)
public class DemoRoot {

    @XmlElement
    private String value;

    public String getValue() {
        return value;
    }

    public void setValue(String value) {
        this.value = value;
    }
}

If you try to unmarshal using XmlAccessType.FIELD and the @XmlElement annotation above the field, then you will unmarshal fine.

If you use XmlAccessType.PROPERTY you will receive the following error:

IllegalAnnotationsException: 1 counts of IllegalAnnotationExceptions Class has two properties of the same name "value"

This is because it takes into consideration both the explicitly annotated with @XmlElement field 'value' and the getters/setters.

And vice versa if you move the @XmlElement annotation on the getter/setter.