Tutorials : Java and JDOM: the perfect couple :

The Element class

When you want to extract data from an Element the most important methods are these:

Not all methods are shown here, but for our examples these are the essential ones. The List's returned from three methods are "live", and any modifications to them will directly influence the contents of the document. To show you what the methods will return I'll first use a very simple example--an element with an attribute and no children:

Another element, "movie", with two children elements:

If you're surprised about the result from getText then it's simply the characters between the movie start- and end-tags when we remove the title- and actor-tags and text.

The Attribute class

The Attribute class doesn't have any "children" so it's quite simple. The most important "getters" for the Attribute class are:

Listing the contents of an XML-file

As the first exercise we'll write a small Java program that lists all the elements and attributes from a given XML-file. It's run from the command line, and you must give the name of an XML-file as the parameter. Starting with the root element the "listElements" method lists the name, textual contents, all the attributes and then the children elements using a recursive call:

package hansen.playground;

import org.jdom.*;
import org.jdom.input.*;
import org.jdom.output.*;
import java.util.*;

/*
* Read an XML file and show all elements (text and attributes) 
*/
public class BuildAndListDocument {

  /*
  * Assume filename as parameter
  */
  public static void main(String[] args) {
    BuildAndListDocument b = new BuildAndListDocument();
    b.buildAndListDocument(args[0]);
  }

  public void buildAndListDocument(String filename) {
    try {
      SAXBuilder builder = new SAXBuilder();
      Document doc = builder.build(filename);
      listElements(doc.getRootElement());
    } catch (JDOMException e) {
      e.printStackTrace();
    }
  }
  
  private void listElements(Element e) {
    System.out.println("*Element, name:" + e.getName() + 
                       ", text:" + e.getText()) ;

    //List all attributes
    List as = e.getAttributes();
    for (Iterator i = as.iterator();i.hasNext();) {
      Attribute a = (Attribute)i.next();
      System.out.println("*Attribute, name:" + a.getName() + 
                         ", value:" + a.getValue()) ;
    }
    
    //List all children
    List c = e.getChildren();
    for (Iterator i = c.iterator();i.hasNext();) {
      Element n = (Element)i.next();
      listElements(n);
    }
  }
  
} 

If we use the movie-element from Table 2 we'll get this printed out:

Important: The jdom-packages that are imported can be downloaded from www.jdom.org. To run the program you'll have to add jdom.jar and xerces.jar (the Xerces parser) to your classpath.

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