Procesarea documentelor XML in limbajul Java

Sa presupunem ca dorim sa procesam fisiserul XML urmator utilizand DOM:

<?xml version="1.0"?>
<!-- Documentul ce retine o carte -->
<CARTE id="10">
        <TITLU>XML Bible</TITLU> 
        <AUTOR>Elliotte Rusty Harold</AUTOR>
        <EDITURA>IDG Books Worldwide</EDITURA>
        <AN_APARITIE>2002</AN_APARITIE>
</CARTE>

In continuare este prezentata secventa Java ce realizeaza operatii asupra acestui XML

package edu.ucv.xml;

import java.io.*;

import javax.xml.parsers.*;
import javax.xml.transform.*;
import javax.xml.transform.dom.*;
import javax.xml.transform.stream.*;

import org.w3c.dom.*;
import org.xml.sax.*;

/**
 *  Exemplu de procesare a documentelor XML folosind DOM
 *
 *@author  Mihai Gabroveanu
 *@created  31 martie 2006
 *@version  1.0
 */

public class TestDOM {

      /**
       *  Afiseaza continutul unui document XML pe ecran.
       *
       *@param  doc Dcoumentul XML.
       *@param  out Output-ul.
       */
      public static void displayDocument(Document doc, OutputStream out) {
            try {
                  
                  TransformerFactory xformFactory = TransformerFactory.newInstance();
                  Transformer idTransform = xformFactory.newTransformer();
          
                  Source input = new DOMSource(doc);
                  Result output = new StreamResult(out);
                  idTransform.transform(input, output);
            } catch (TransformerException e) {
            } catch (TransformerFactoryConfigurationError ex) {
            }
      }


      /**
       *  The main program for the TestDOM class
       *
       *@param  args The command line arguments
       */
      public static void main(String[] args) {
            //Se obtine o instanta de parser
            DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

            DocumentBuilder docBuilder = null;
            factory.setValidating(false);
            try {
                  docBuilder = factory.newDocumentBuilder();
            } catch (ParserConfigurationException e) {
                  System.out.println("Eroare la crearea Document Builder-ului:" + e.getMessage());
                  System.exit(1);
            }

            String numeFisier = "carte.xml";
            Document doc = null;
            try {
                  //Incarc documentul XML
                  doc = docBuilder.parse(new File(numeFisier));
            } catch (SAXException e) {
                  System.err.println("Eroare la parsarea documentului [" + numeFisier + "]:" + e.getMessage());
                  System.exit(1);
            } catch (IOException e) {
                  System.err.println("Eroare I/O la deschierea fisierului [" + numeFisier + "]:" + e.getMessage());
                  System.exit(1);
            }
            //Obtin elelementul radacina
            Element rootElement = doc.getDocumentElement();
            System.out.println("Numele elementului radacina este:" + rootElement.getNodeName());

            //Lista copiilor
            System.out.println("Lista copiilor pentru elementul:" + rootElement.getNodeName());
            NodeList rootNodeList = rootElement.getChildNodes();
            for (int i = 0; i < rootNodeList.getLength(); i++) {
                  Node childNode = rootNodeList.item(i);
                  if (childNode.getNodeType() == Node.ELEMENT_NODE) {
                        System.out.print(" " + childNode.getNodeName());
                        Node firstChild = childNode.getFirstChild();
                        //incerc sa obtin valoarea din aceste Elemente
                        if (firstChild != null && firstChild.getNodeType() == Node.TEXT_NODE) {
                              //daca primul copil al lui childNode este nod text (CDATA) atunci obtin valoarea acestuia
                              Text textNode = (Text) firstChild;
                              System.out.println("=[" + textNode.getNodeValue() + "]");
                        } else {
                              System.out.println("=[]");
                        }

                  }
            }

            if (rootElement.hasAttribute("id")) {
                  System.out.println("Elementul radacina are atributul id='" + rootElement.getAttribute("id") + "'");
            }

            //Construiesc un element TIRAJ cu valoarea 1000
            Element tirajElement = doc.createElement("TIRAJ");
            Text continutTirajElement = doc.createTextNode("1000");
            //Apendez la TIRAJ valoarea
            tirajElement.appendChild(continutTirajElement);

            //Adaug elementul tiraj ca fiu al lui CARTE.
            rootElement.appendChild(tirajElement);

        displayDocument(doc, System.out);
      }
}

SAX = Simple API for XML ofera posibilitatea parcurgeri secventiale ale documentelor XML. Pe masura ce documentul este parcurs de catre parser sunt generate automat evenimente ca de exemplu: inceputul, sfarsitul unui document, inceputul si sfarsitul unui element, etc, ce pot fi interceptate in vederea realizarii anumitor operatii.

In vederea procesarii unui document XML cu SAX trebuie parcursi urmatorii pasi:

In continuare este prezentat un mic exemplu de prelucrare a unui document XML utilizand SAX:

import java.io.*;

import javax.xml.parsers.*;

/**
 *  SAX Demo
 *
 *@author  Mihai Gabroveanu
 *@created  07 aprilie 2006
 *@version  1.0
 */

public class SAXTest {

      /**
       *  The main program for the SAXTest class
       *
       *@param  args The command line arguments
       */
      public static void main(String[] args) {
            String xmlFileName = "carte.xml";

            DemoSAXHandler handler = new DemoSAXHandler(new OutputStreamWriter(System.out));

            SAXParserFactory factory = SAXParserFactory.newInstance();
            try {

                  // Parse the input
                  SAXParser saxParser = factory.newSAXParser();
                  saxParser.parse(new File(xmlFileName), handler);

            } catch (Throwable t) {
                  t.printStackTrace();
            }
            System.exit(0);
      }
}

    

Clasa ce trateaza evenimentele genrate la parsare este urmatoarea:

import java.io.*;
import org.xml.sax.*;
import org.xml.sax.helpers.*;

/**
 *  Clasa ce trateaza evenimentele generate de parser.
 *
 *@author  Mihai Gabroveanu
 *@created  07 aprilie 2006
 */
public class DemoSAXHandler extends DefaultHandler {

      /**
       *  Description of the Field
       */
      private Writer out;
      /**
       *  Spatiul de indentare.
       */
      private String indentString = "    ";

      /**
       *  Nuvelul curednt de indentare.
       */
      private int indentLevel = 0;

      /**
       *  Constructor for the DemoSAXHandler object
       *
       *@param  out Description of the Parameter
       */
      public DemoSAXHandler(Writer out) {
            this.out = out;
      }

      /**
       *  Metoda apelata atunci cand se incepe parsarea documentului.
       *
       *@exception  SAXException Daca a aparut o eroare de parsare.
       */
      public void startDocument() throws SAXException {
            nl();
            nl();
            emit("START DOCUMENT");
            nl();
            emit("<?xml version='1.0' encoding='UTF-8'?>");
      }

      /**
       *  Metoda apelata atunci cand se detecteaza sfarsitul unui document.
       *
       *@exception  SAXException Daca a aparut o eroare de parsare.
       */
      public void endDocument() throws SAXException {
            nl();
            emit("END DOCUMENT");
            try {
                  nl();
                  out.flush();
            } catch (IOException e) {
                  throw new SAXException("I/O error", e);
            }
      }

      /**
       *  Metoda invocata cand se detecteaza inceputul unui nou element.
       *
       *@param  namespaceURI Namespace-ul elementului.
       *@param  sName Numele local (simple name).
       *@param  qName Numele calificat (qualified) name.
       *@param  attrs Lista de atribute.
       *@exception  SAXException Daca a aparut o eroare de parsare.
       */
      public void startElement(String namespaceURI, String sName, String qName, Attributes attrs)
                   throws SAXException {
            indentLevel++;
            nl();
            emit("ELEMENT: ");
            String eName = sName;
            // element name
            if ("".equals(eName)) {
                  eName = qName;
            }
            // namespaceAware = false
            emit("<" + eName);
            if (attrs != null) {
                  for (int i = 0; i < attrs.getLength(); i++) {
                        String aName = attrs.getLocalName(i);
                        // Attr name
                        if ("".equals(aName)) {
                              aName = attrs.getQName(i);
                        }
                        nl();
                        emit("   ATTR: ");
                        emit(aName);
                        emit("\t\"");
                        emit(attrs.getValue(i));
                        emit("\"");
                  }
            }
            if (attrs.getLength() > 0) {
                  nl();
            }
            emit(">");
      }

      /**
       *  Metoda invocata cand se detecteaza sfarsitul unui element.
       *
       *@param  namespaceURI Namespace-ul elementului.
       *@param  sName Numele local (simple name).
       *@param  qName Numele calificat (qualified) name.
       *@exception  SAXException Daca a aparut o eroare de parsare.
       */
      public void endElement(String namespaceURI, String sName, String qName) throws SAXException {
            nl();
            emit("END_ELM: ");
            emit("</" + sName + ">");
            indentLevel--;

      }

      /**
       *  Metoda apelata cand se intalnesc date caracter.
       *
       *@param  buf Caractele citite
       *@param  offset
       *@param  len
       *@exception  SAXException Daca a aparut o eroare de parsare.
       */
      public void characters(char buf[], int offset, int len) throws SAXException {
            nl();
            emit("CHARS:   ");
            String s = new String(buf, offset, len);
            if (!s.trim().equals("")) {
                  emit(s);
            }
            ;
      }

       /**
       *  Metoda invocata cand se intalneste o instructiune de procesare.
       *
       *@param  target Numele instructiunii de procesare.
       *@param  data
       *@exception  SAXException Daca a aparut o eroare de parsare.
       */
      public void processingInstruction(String target, String data) throws SAXException {
            nl();
            emit("PROCESS: ");
            emit("<?" + target + " " + data + "?>");
      }

      //===========================================================
      // Metodele din SAX ErrorHandler ce se ocupa cu procesarea erorilor.
      //===========================================================

      /**
       *  Trateaza erorile fatale.
       *
       *@param  e Eroarea intalnita.
       *@exception  SAXParseException Description of the Exception
       */
      public void error(SAXParseException e) throws SAXParseException {
            throw e;
      }

      /**
       *  Trateaza warningurile
       *
       *@param  err Eroarea intalnita.
       *@exception  SAXParseException Description of the Exception
       */
      public void warning(SAXParseException err) throws SAXParseException {
            System.out.println("** Warning"
                        + ", line " + err.getLineNumber()
                        + ", uri " + err.getSystemId());
            System.out.println("   " + err.getMessage());
      }

      //===========================================================
      // Metode utilitare
      //===========================================================

      /**
       *  Mapeaza erorile I/O in erori SAX.
       *
       *@param  s Description of the Parameter
       *@exception  SAXException Description of the Exception
       */
      private void emit(String s) throws SAXException {
            try {
                  out.write(s);
                  out.flush();
            } catch (IOException e) {
                  throw new SAXException("I/O error", e);
            }
      }

      /**
       *  Afiseaza o linie noua si indenteaza corespunzator.
       *
       *@exception  SAXException Daca a aparut o exceptie de I/O.
       */
      private void nl() throws SAXException {
            String lineEnd = System.getProperty("line.separator");
            try {
                  out.write(lineEnd);
                  for (int i = 0; i < indentLevel; i++) {
                        out.write(indentString);
                  }
            } catch (IOException e) {
                  throw new SAXException("I/O error", e);
            }
      }
}