default initialization value for jaxb generated class
@XmlRootElement
@XmlAccessorType(XmlAccessType.PROPERTY)
public class foo {
    boolean bar = true;

    boolean getBar () {
        return this.bar;
    }

    void setBar (boolean bar) {
        this.bar = bar;
    }
}

@XmlElement (defaultvalue="true")
boolean getBar () {
    return this.bar;
}

<xs:element default="true" name="bar" type="xs:boolean"/>

@XmlAccessorType(XmlAccessType.FIELD)
public class foo {
    @XmlElement(defaultValue = "true")
    protected boolean bar;

    boolean getBar () {
        return this.bar;
    }

    void setBar (boolean bar) {
        this.bar = bar;
    }
}