Dynamic Proxy to Indent StAX Output

PrettyPrintHandler

public class PrettyPrintHandler implements InvocationHandler {

  private static Logger LOGGER = Logger.getLogger(PrettyPrintHandler.class.getName());
  private final XMLStreamWriter target;
  private int depth = 0;
  private final Map<Integer, Boolean> hasChildElement = new HashMap<Integer, Boolean>();
  private static final String INDENT_CHAR = " ";
  private static final String LINEFEED_CHAR = "\n";

  public PrettyPrintHandler(XMLStreamWriter target) {
    this.target = target;
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    String m = method.getName();
    if (LOGGER.isDebugEnabled()) {
      LOGGER.debug("XML event: " + m);
    }
    // Needs to be BEFORE the actual event, so that for instance the
    // sequence writeStartElem, writeAttr, writeStartElem, writeEndElem, writeEndElem
    // is correctly handled
    if ("writeStartElement".equals(m)) {
      // update state of parent node
      if (depth > 0) {
        hasChildElement.put(depth - 1, true);
      }
      // reset state of current node
      hasChildElement.put(depth, false);
      // indent for current depth
      target.writeCharacters(LINEFEED_CHAR);
      target.writeCharacters(repeat(depth, INDENT_CHAR));
      depth++;
    }
    else if ("writeEndElement".equals(m)) {
      depth--;
      if (hasChildElement.get(depth) == true) {
        target.writeCharacters(LINEFEED_CHAR);
        target.writeCharacters(repeat(depth, INDENT_CHAR));
      }
    }
    else if ("writeEmptyElement".equals(m)) {
      // update state of parent node
      if (depth > 0) {
        hasChildElement.put(depth - 1, true);
      }
      // indent for current depth
      target.writeCharacters(LINEFEED_CHAR);
      target.writeCharacters(repeat(depth, INDENT_CHAR));
    }
    method.invoke(target, args);
    return null;
  }

  private String repeat(int d, String s) {
    String _s = "";
    while (d-- > 0) {
      _s += s;
    }
    return _s;
  }
}