Java XML processing with dom4j

XML DOM Parsing

// build DOM 
URL url = new URL("<path-to-file>");
SAXReader reader = new SAXReader();
Document document = reader.read(url);

XPath Navigation

Use XPath expression to navigate the document tree.

Processing a single node

Node node = document.selectSingleNode("/html/head/meta[@name=keywords]");
String content = node.valueOf("@content");

To process multiple results, we need to use a List

Document document; // assume is instantiated
// all src attributes of any img element
List list = document.selectNodes("//**/img/@src");
// loop the list
for( Iterator it = list.iterator(); it.hasNext();  ){
  Attribute att = (Attribute) it.next();
  String uri = att.getValue();
}

Document Creation

You can create a docuemnt from scratch by using the DocumentHelper#createDocuemnt(). Adding nodes and attributes is easy and intuitive.

Document document = DocumentHelper.createDocument();
element root = document.addElement("root");
// add a child
Element elChild1 = root.addElement("child")
  .addAttribute("name","Nicholas")
  .addAttribute("age","15")
  .addText("Nic is the first child);
// add a second child
Element elChild2 = root.addElement("child")
  .addAttribute("name","Valentine")
  .addAttribute("age","12")
  .addText("Vale is the second child);

Writing document to File

To write a document you can use the Document.write() method

FileWriter fw = new FileWriter("my-out-file.xml");
document.write( fw );

You can change writing formats and parameters. Below there is a code example.

// prepare an output format
OutputFormat format = OutputFormat.createPrettyPrint();
XmlWriter xw = new XMLWriter( System.out, format );
xw.write( document );

Converting to and from String

You can convert a document, or a node into corresponding xml String.

// here  get xml of entire document
String text = document.asXML();

If you have XML in a String, you can get build the represented document

String xmlText ="<root><child>Nich</child><child>Vale</child></root>";
Document doc = DocumentHelper.parseText(xmlText);

Apply XSL-Transform

To apply XSL-Transform to a document you can use the JAXP Api from sun, by using any XSLT engine you want, like Xalan or Saxon.

Document document; //.. assume instantiated
String xslturi; //..
TransformerFactory tf = TransformerFactory.newInstance();
Transformer t = tf.newTransformer( new StreamSource(xslturi) );
// executes the transform
DocumentSource source = new DocumentSource( document );
DocumentResult result = new DocumentResult();
t.transform( source, result );
// get output document
Document output = result.getDocument();

References

• dom4j quickstart guide, dom4j on GitHub