IDTagger

import org.apache.xerces.parsers.DOMParser;
import org.w3c.dom.*;
import org.xml.sax.*;
import java.io.IOException;
import org.apache.xml.serialize.*;

public class IDTagger {

  int id = 1;

  public void processNode(Node node) {
    
    if (node.getNodeType() == Node.ELEMENT_NODE) {
      
      Element element = (Element) node;
      String currentID = element.getAttribute("ID");
      if (currentID == null || currentID.equals("")) {
        element.setAttribute("ID", "_" + id);
        id = id + 1; 
      }
    }
    
  }

  // note use of recursion
  public void followNode(Node node) {
    
    processNode(node);
    if (node.hasChildNodes()) {
      NodeList children = node.getChildNodes();
      for (int i = 0; i < children.getLength(); i++) {
        followNode(children.item(i));
      } 
    }
    
  }

  public static void main(String[] args) {
     
    DOMParser parser  = new DOMParser();
    IDTagger iterator = new IDTagger();
    
    for (int i = 0; i < args.length; i++) {
      try {
        // Read the entire document into memory
        parser.parse(args[i]); 
       
        Document document = parser.getDocument();
        iterator.followNode(document);
        
        // now we serialize the document...
        OutputFormat format = new OutputFormat(document);
        XMLSerializer serializer 
         = new XMLSerializer(System.out, format);
        serializer.serialize(document);       
        
      }
      catch (SAXException ex) {
        System.err.println(ex); 
      }
      catch (IOException ex) {
        System.err.println(ex); 
      }
      
    }
  } // end main
}