How to make newlines between attributes in XML file by using dom4j?

I want to generate a xml file in the following format by using java : each attribute should be in separate line.

<parameters>
    <parameter 
        name="Tom" 
        city="York" 
        number="123"
    />
</parameters>

But I can only get all attributes in one line

<parameters>
    <parameter name="Tom" city="York" number="123"/>
</parameters>

I'm using dom4j, could anyone tell how I can make it? Does dom4j supports this kind of format? Thanks.

You cannot do it with the XMLWriter unless you want to substantially rewrite the main logic. However, since XMLWriter is also a SAX ContentHandler it can consume SAX events and serialize them to XML, and in this mode of operation, XMLWriteruses a different code path which is easier to customize. The following sub class will give you almost what you want, except that empty elements will not use the short form <element/>. Maybe that can be fixed by further tweaking.

static class ModifiedXmlWriter extends XMLWriter {
    // indentLevel is private, need reflection to read it
    Field il;

    public ModifiedXmlWriter(OutputStream out, OutputFormat format) throws UnsupportedEncodingException {
        super(out, format);
        try {
            il = XMLWriter.class.getDeclaredField("indentLevel");
            il.setAccessible(true);
        } catch (NoSuchFieldException e) {
            throw new RuntimeException(e);
        }
    }

    int getIndentLevel() {
        try {
            return il.getInt(this);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    protected void writeAttributes(Attributes attributes) throws IOException {
        int l = getIndentLevel();
        setIndentLevel(l+1);
        super.writeAttributes(attributes);
        setIndentLevel(l);
    }

    @Override
    protected void writeAttribute(Attributes attributes, int index) throws IOException {
        writePrintln();
        indent();
        super.writeAttribute(attributes, index);

    }
}

public static void main(String[] args) throws Exception {
    String XML = "<parameters>\n" + 
            "    <parameter name=\"Tom\" city=\"York\" number=\"123\"/>\n" + 
            "</parameters>";

    Document doc = DocumentHelper.parseText(XML);

    XMLWriter writer = new ModifiedXmlWriter(System.out, OutputFormat.createPrettyPrint());

    SAXWriter sw = new SAXWriter(writer);
    sw.write(doc);

}

Sample output:

<?xml version="1.0" encoding="UTF-8"?>

<parameters>
  <parameter
     name="Tom"
     city="York"
     number="123"></parameter> 
</parameters>