Modifying XML Documents

In the previous chapter, we saw that the Java DOM parser has several methods , such as insertBefore and addChild , that let you modify a document in memory. SAX parsers don't give you access to the whole document tree at once, so no similar methods exist here.

However, you can "modify" the structure of a document when using a SAX parser simply by calling various callback methods yourself. For example, you can modify ch12_01.xml to create ch12_11.xml, adding a <MIDDLE_NAME> element with the text "XML" to each <PERSON> element in addition to the <FIRST_NAME> and <LAST_NAME> elements. It's easy enough to do the same here using SAX methods. All I have to do is to wait for a <FIST_NAME> element and then "create" a new element by calling the startElement , characters , and endElement callbacks myself :

 public void endElement(String uri, String localName, String qualifiedName)  {     indent = indent.substring(0, indent.length() - 4);     displayStrings[numberDisplayLines] = indent;     displayStrings[numberDisplayLines] += "</";     displayStrings[numberDisplayLines] += qualifiedName;     displayStrings[numberDisplayLines] += '>';     numberDisplayLines++;  if (qualifiedName.equals("FIRST_NAME")) {   startElement("", "MIDDLE_NAME", "MIDDLE_NAME", null);   characters("XML".toCharArray(), 0, "XML".length());   endElement("", "MIDDLE_NAME", "MIDDLE_NAME");   }  } 

In the main method, I'll write this new document out to ch12_11.xml:

 public static void main(String args[])      {         displayDocument(args[0]);  try {   FileWriter filewriter = new FileWriter("ch12_11.xml");   for(int loopIndex = 0; loopIndex < numberDisplayLines; loopIndex++){   filewriter.write(displayStrings[loopIndex].toCharArray());   filewriter.write('\n');   }   filewriter.close();   }   catch (Exception e) {   e.printStackTrace(System.err);   }  } } 

And that's ithere's the whole code:

Listing ch12_10.java

 import org.xml.sax.*; import org.xml.sax.helpers.DefaultHandler; import javax.xml.parsers.*; import java.io.*; public class ch12_10 extends DefaultHandler {     static String displayStrings[] = new String[1000];     static int numberDisplayLines = 0;     static String indent = "";     public void displayDocument(String uri)     {         DefaultHandler handler = this;         SAXParserFactory factory = SAXParserFactory.newInstance();         try {             SAXParser saxParser = factory.newSAXParser();             saxParser.parse(new File(uri), handler);         } catch (Throwable t) {}     }     public void startDocument()     {         displayStrings[numberDisplayLines] = indent;         displayStrings[numberDisplayLines] += "<?xml version=\"1.0\" encoding=\""+             "UTF-8" + "\"?>";         numberDisplayLines++;     }     public void processingInstruction(String target, String data)     {         displayStrings[numberDisplayLines] = indent;         displayStrings[numberDisplayLines] += "<?";         displayStrings[numberDisplayLines] += target;         if (data != null && data.length() > 0) {             displayStrings[numberDisplayLines] += ' ';             displayStrings[numberDisplayLines] += data;         }         displayStrings[numberDisplayLines] += "?>";         numberDisplayLines++;     }     public void startElement(String uri, String localName, String qualifiedName,         Attributes attributes)     {         displayStrings[numberDisplayLines] = indent;         indent += "    ";         displayStrings[numberDisplayLines] += '<';         displayStrings[numberDisplayLines] += qualifiedName;         if (attributes != null) {             int numberAttributes = attributes.getLength();             for (int loopIndex = 0; loopIndex < numberAttributes; loopIndex++) {                 displayStrings[numberDisplayLines] += ' ';                 displayStrings[numberDisplayLines] += attributes.getLocalName(loopIndex);                 displayStrings[numberDisplayLines] += "=\"";                 displayStrings[numberDisplayLines] += attributes.getValue(loopIndex);                 displayStrings[numberDisplayLines] += '"';             }         }         displayStrings[numberDisplayLines] += '>';         numberDisplayLines++;     }     public void characters(char characters[], int start, int length)     {         String characterData = (new String(characters, start, length)).trim();         if(characterData.indexOf("\n") < 0 && characterData.length() > 0) {             displayStrings[numberDisplayLines] = indent;             displayStrings[numberDisplayLines] += characterData;             numberDisplayLines++;         }     }     public void ignorableWhitespace(char characters[], int start, int length)     {         //characters(characters, start, length);     }     public void endElement(String uri, String localName, String qualifiedName)     {         indent = indent.substring(0, indent.length() - 4);         displayStrings[numberDisplayLines] = indent;         displayStrings[numberDisplayLines] += "</";         displayStrings[numberDisplayLines] += qualifiedName;         displayStrings[numberDisplayLines] += '>';         numberDisplayLines++;         if (qualifiedName.equals("FIRST_NAME")) {             startElement("", "MIDDLE_NAME", "MIDDLE_NAME", null);             characters("XML".toCharArray(), 0, "XML".length());             endElement("", "MIDDLE_NAME", "MIDDLE_NAME");         }     }     public void warning(SAXParseException exception)     {         System.err.println("WARNING! " +             exception.getMessage());     }     public void error(SAXParseException exception)     {         System.err.println("ERROR! " +             exception.getMessage());     }     public void fatalError(SAXParseException exception)     {         System.err.println("FATAL ERROR! " +             exception.getMessage());     }     public static void main(String args[])     {         ch12_10 obj = new ch12_10();         obj.displayDocument(args[0]);         try {             FileWriter filewriter = new FileWriter("ch12_11.xml");             for(int loopIndex = 0; loopIndex < numberDisplayLines; loopIndex++){                 filewriter.write(displayStrings[loopIndex].toCharArray());                 filewriter.write('\n');             }             filewriter.close();         }         catch (Exception e) {             e.printStackTrace(System.err);         }     } } 

And here's what the resulting document, ch12_11.xml, looks like, with the new <MIDDLE_NAME> elements:

Listing ch12_11.xml

 <?xml version="1.0" encoding="UTF-8"?> <DOCUMENT>     <CUSTOMER>         <NAME>             <LAST_NAME>                 Smith             </LAST_NAME>             <FIRST_NAME>                 Sam             </FIRST_NAME>  <MIDDLE_NAME>   XML   </MIDDLE_NAME>  </NAME>         <DATE>             October 15, 2003         </DATE>         <ORDERS>             <ITEM>                 <PRODUCT>                     Tomatoes                 </PRODUCT>                 <NUMBER>                     8                 </NUMBER>                 <PRICE>                     .25                 </PRICE>             </ITEM>             <ITEM>                 <PRODUCT>                     Oranges                 </PRODUCT>                 <NUMBER>                     24                 </NUMBER>                 <PRICE>                     .98                 </PRICE>             </ITEM>         </ORDERS>     </CUSTOMER>     <CUSTOMER>         <NAME>             <LAST_NAME>                 Jones             </LAST_NAME>             <FIRST_NAME>                 Polly             </FIRST_NAME>  <MIDDLE_NAME>   XML   </MIDDLE_NAME>  </NAME>         <DATE>             October 20, 2003         </DATE>         <ORDERS>             <ITEM>                 <PRODUCT>                     Bread                 </PRODUCT>                 <NUMBER>                     12                 </NUMBER>                 <PRICE>                     .95                 </PRICE>             </ITEM>             <ITEM>                 <PRODUCT>                     Apples                 </PRODUCT>                 <NUMBER>                     6                 </NUMBER>                 <PRICE>                     .50                 </PRICE>             </ITEM>         </ORDERS>     </CUSTOMER>     <CUSTOMER>         <NAME>             <LAST_NAME>                 Weber             </LAST_NAME>             <FIRST_NAME>                 Bill             </FIRST_NAME>  <MIDDLE_NAME>   XML   </MIDDLE_NAME>  </NAME>         <DATE>             October 25, 2003         </DATE>         <ORDERS>             <ITEM>                 <PRODUCT>                     Asparagus                 </PRODUCT>                 <NUMBER>                     12                 </NUMBER>                 <PRICE>                     .95                 </PRICE>             </ITEM>             <ITEM>                 <PRODUCT>                     Lettuce                 </PRODUCT>                 <NUMBER>                     6                 </NUMBER>                 <PRICE>                     .50                 </PRICE>             </ITEM>         </ORDERS>     </CUSTOMER> </DOCUMENT> 

That finishes our work with the Java XML parsers for the moment. In the next chapter, I'm going to start working with XSL transformations.