Insert new element to an XML file using SAX Filter

Question

I have an XMl file that looks like:

  
    2
    

        

Answer 1

Using @Jorn Horstmann's (http://stackoverflow.com/users/139595/jorn-horstmann) answer from above you can easily add the missing elements. But to write the results to an XML file you should use the TransformerHandler.

Just create a very basic ContentHandler and use it instead of the DefaultHandler. In the ContentHandler you can implement all the basic functions (startDocument, startElement etc.) and add every element to a new Transformer. e.g. In your startDocument function:

Transformer t = hd.getTransformer();
t.setOutputProperty(OutputKeys.ENCODING, "UTF-8");
t.setOutputProperty(OutputKeys.METHOD, "xml");
t.setOutputProperty(OutputKeys.INDENT, "yes");
hd.startDocument();

And then (in each other function) add this: e.g. for startElement:

hd.startElement(uri,localName,name,attributes);

Finally you can write all this to a file in the endDocument method.

Answer 2

Correct me if i'm wrong but i think XMLReader and XMLFilter are not really supposed to change a document. I can provide a different approach which with you can change the content of your document too:

public class ExtXMLConfig {
private JAXBContext context;
private Marshaller m;
private Unmarshaller um;
private Schema schema = null;

/**
 * Creates an ExtXMLConfig-object, which uses rootClass as object to parse
 * and save XML-files.
 * 
 * @param rootClass
 *            the class use create/parse xml-files from
 * @throws JAXBException
 */
public ExtXMLConfig(Class<?> rootClass) throws JAXBException {
    context = JAXBContext.newInstance(rootClass);

    init();
}

/**
 * Creates an ExtXMLConfig, which uses a classPath like javax.xml.bin to use
 * all classes in that path to parse and write xml-files
 * 
 * @param classPath
 *            the class path containing all needed java-objects
 * @throws JAXBException
 */
public ExtXMLConfig(String classPath) throws JAXBException {
    context = JAXBContext.newInstance(classPath);

    init();
}

/**
 * Parses a xml-file into a JavaObject.
 * 
 * @param file
 *            path to the xml-file
 * @return a java-Object
 */
public Object load(String file) {
    return load(new File(file));
}

/**
 * Parses a xml-file into a JavaObject.
 * 
 * @param xml
 *            File-object representing the xml-file
 * @return a java-Object
 */
public Object load(File xml) {
    um.setSchema(schema);

    if (xml.exists() && xml.isFile()) {
        try {
            return um.unmarshal(xml);
        } catch (JAXBException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    } else {
        System.out.println("Failed to open file: " + xml.getAbsolutePath());
    }

    return null;
}

/**
 * Saves a object into a xml-file.
 * 
 * @param xml
 *            the object to save
 * @param file
 *            path to the file to save to
 */
public void save(Object xml, String file) {
    save(xml, new File(file));
}

/**
 * Saves a object into a xml-file.
 * 
 * @param xml
 *            the object to save
 * @param file
 *            File-object representing the file to save to
 */
public void save(Object xml, File file) {
    if (xml != null) {
        m.setSchema(schema);

        if (!file.isDirectory()) {
            try {
                if (!file.exists()) {
                    file.createNewFile();
                }

                m.marshal(xml, file);
            } catch (JAXBException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

/**
 * Returns a formatted string representation of a xml-file given as a
 * java-Object.
 * 
 * @param xml
 *            the java-object to parse the xml from.
 * @return a formatted string representation of the given object
 */
public String toString(Object xml) {
    StringWriter out = new StringWriter();
    try {
        m.setSchema(schema);
        m.marshal(xml, out);

        return out.toString();
    } catch (JAXBException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

    return null;
}

private void init() throws JAXBException {
    m = context.createMarshaller();
    m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
    m.setProperty(Marshaller.JAXB_ENCODING, "UTF-8");

    um = context.createUnmarshaller();
}

Using this class to parse your xml-Files you would only need a Class like this:

@XmlRootElement // used to parse this class as xml-Root
public class Game {
   private Move moves;

   public Game() {};

   public void setMove(Move moves) {
      this.moves = moves;
   }

   public Moves getMoves() {
      return this.moves;
   }
}

with Move being an instance of another class which has the fields you need and also has a annotation for XmlRootElement.

I hope this helps.

Answer 3

Your XMLFilter should delegate to another ContentHandler that serializes the document based on the sax events.

SAXTransformerFactory factory = (SAXTransformerFactory)TransformerFactory.newInstance();
TransformerHandler serializer = factory.newTransformerHandler();
Result result = new StreamResult(...);
serializer.setResult(result);

XMLFilterImpl filter = new MyFilter();
filter.setContentHandler(serializer);

XMLReader xmlreader = XMLReaderFactory.createXMLReader();
xmlreader.setFeature("http://xml.org/sax/features/namespaces", true);
xmlreader.setFeature("http://xml.org/sax/features/namespace-prefixes", true);
xmlreader.setContentHandler(filter);

xmlreader.parse(new InputSource(...));

Your callback should delegate to the super implementation, which forwards the events to the serializing ContentHandler.

public void startElement(String namespaceURI, String localName, String qName, Attributes atts) throws SAXException {
    super.startElement(namespaceURI, localName, qName, atts);
    ...
}

In your endElement callback you can check if your are at the final closing tag and add additional sax events.

public void endElement(String namespaceURI, String localName, String qName) throws SAXException {
    super.endElement(namespaceURI, localName, qName);
    if ("game".equals(localName)) {
        super.startElement("", "statistics", "statistics", new AttributesImpl());
        char[] chars = String.valueOf(num).toCharArray();
        super.characters(chars, 0, chars.length);
        super.endElement("", "statistics", "statistics");
    }
    ...
}