How to add a default name space with dom4j?

Question

I would like to add a default name space to the root element of a XML document using dom4j, like in the following snippet. What is the correct way to do this with dom4j?

<?xml version="1.0" encoding="utf-8" ?>
<animals xmlns="http://zoo.domain.org/schema/animals" >
    <animal id="1">
        <elephant>
            <name>Jumbo</name>
        </elephant>
    </animal>
</animals>

The dom4j API does provide the method Element#addNamespace but the javadoc tells that the prefix may not be blank. The following code will result in the expected namespace for animals though:

Document document = DocumentHelper.createDocument();
Element animals = document.addElement("animals")
        .addNamespace("", "http://zoo.domain.org/schema/animals");
Element animal = animals.addElement("animal")
        .addAttribute("id", "1");
animal.addElement("elephant")
        .addElement("name")
        .addText("Jumbo");

// write document to file etc.
...

... but the child element animal gets an empty string as default namespace, which is not what I want:

<?xml version="1.0" encoding="UTF-8"?>
<animals xmlns="http://zoo.domain.org/schema/animals">
    <animal xmlns="" id="1">
        <elephant>
            <name>Jumbo</name>
        </elephant>
    </animal>
</animals>

Answer 1

The method Document#addElement (but also Element#addElement) accepts a second parameter namespaceURI. That does the trick, adding the default namespace to the XML element.

The following code will result in the expected XML.

Document document = DocumentHelper.createDocument();
Element animals = document.addElement("animals", "http://zoo.domain.org/schema/animals");
Element animal = animals.addElement("animal")
        .addAttribute("id", "1");
animal.addElement("elephant")
        .addElement("name")
        .addText("Jumbo");

// write document to file etc.
...

Also worth mentioning is that in case you would like to create an Element on its own DocumentFactory#createElement has an overloaded version that accepts a namespaceURI as well. DocumentHelper#createElement does not have such an overloaded method.

Answer 2

You are not creating the document (root) element.

Document document = DocumentHelper.createDocument();
Element root = document.addElement( "animals" );
// TODO the rest of your code

Eventually, you'll pass your document to an XML writer to write (save) the document. Also, from Javadoc:

Element addNamespace​(java.lang.String prefix, java.lang.String uri) Adds a namespace to this element for use by its child content Parameters: prefix - is the prefix to use, which should not be null or blank

One thing you could try is create an instance of Namespace passing a empty String to the constructor and use the Element.add() method instead. The Javadoc of Namespace doesn't indicate that the prefix can't be blank.