Question

I am trying to make JAXB do not marshal empty tags when string is empty.
I can make it by creating XmlAdapter where insted empty string null would be returned. But in that way, I will have to annotate each attribute with this adapter.

Is there any way to make it more global?

Answer 1

EclipseLink JAXB (MOXy) will let you specify the XmlAdapter for java.lang.String at the package level (I’m the MOXy tech lead):

package-info

@XmlJavaTypeAdapter(value=StringAdapter.class, type=String.class)
package example;

import javax.xml.bind.annotation.adapters.XmlJavaTypeAdapter;

StringAdapter

package example;

import javax.xml.bind.annotation.adapters.XmlAdapter;

public class StringAdapter extends XmlAdapter<String, String> {

    @Override
    public String unmarshal(String v) throws Exception {
        return v;
    }

    @Override
    public String marshal(String v) throws Exception {
        if("".equals(v)) {
            return null;
        }
        return v;
    }

}

Root

package example;

import javax.xml.bind.annotation.XmlRootElement;

@XmlRootElement
public class Root {

    private String foo;
    private String bar;

    public String getFoo() {
        return foo;
    }

    public void setFoo(String foo) {
        this.foo = foo;
    }

    public String getBar() {
        return bar;
    }

    public void setBar(String bar) {
        this.bar = bar;
    }

}

jaxb.properties

To use MOXy as your JAXB provider you need to include a file named jaxb.properties in the same package as your model classes with the following entry:

javax.xml.bind.context.factory=org.eclipse.persistence.jaxb.JAXBContextFactory

Demo

package example;

import javax.xml.bind.JAXBContext;
import javax.xml.bind.Marshaller;

public class Demo {

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

        Root root = new Root();
        root.setFoo("");
        root.setBar("");

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

}

Note

Due to what I feel is a bug in the JAXB reference implementation, the following exception is thrown if you use the version of JAXB included in Java SE 6:

Exception in thread "main" java.lang.NullPointerException
    at com.sun.xml.bind.v2.runtime.output.Encoded.setEscape(Encoded.java:107)
    at com.sun.xml.bind.v2.runtime.output.UTF8XmlOutput.doText(UTF8XmlOutput.java:315)
    at com.sun.xml.bind.v2.runtime.output.UTF8XmlOutput.text(UTF8XmlOutput.java:299)
    at com.sun.xml.bind.v2.runtime.output.IndentingUTF8XmlOutput.text(IndentingUTF8XmlOutput.java:153)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.leafElement(XMLSerializer.java:325)
    at com.sun.xml.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl$1.writeLeafElement(RuntimeBuiltinLeafInfoImpl.java:210)
    at com.sun.xml.bind.v2.model.impl.RuntimeBuiltinLeafInfoImpl$1.writeLeafElement(RuntimeBuiltinLeafInfoImpl.java:209)
    at com.sun.xml.bind.v2.runtime.reflect.TransducedAccessor$CompositeTransducedAccessorImpl.writeLeafElement(TransducedAccessor.java:250)
    at com.sun.xml.bind.v2.runtime.property.SingleElementLeafProperty.serializeBody(SingleElementLeafProperty.java:98)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeBody(ClassBeanInfoImpl.java:340)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsSoleContent(XMLSerializer.java:593)
    at com.sun.xml.bind.v2.runtime.ClassBeanInfoImpl.serializeRoot(ClassBeanInfoImpl.java:324)
    at com.sun.xml.bind.v2.runtime.XMLSerializer.childAsRoot(XMLSerializer.java:494)
    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 example.Demo.main(Demo.java:18)