XML Events,SAX Parser in Java,ContentHandler SAX,Locating the Notified Events

Locating the Notified Events

In this section, you will learn to locate (line and column number) the generated events while parsing a XML file using SAX APIs.

Description of program:

This program takes a XML file at the console. Before parsing, the setContentHandler() method invokes the XMLReader object and it takes DefaultHandler object. The setContentHandler method allows an application to register a content event handler. The parser starts parsing a XML document, as soon as it encounters the root tag at at Line no: 1 Column no: 1, the startDocument() method is called and the program displays "startDocument() method called at Line no: 1 Column no: 1" at the console. When parser encounters the first elements, it calls the startElement() method and it displays "startElement() method called at Line no: 1 Column no: 19. Similarly, the parser calls characters(), endElement() and endDocument() methods. The parser displays appropriate messages according to the events generated while parsing a xml document.

Here is the XML File: sample.xml

<Employee-detail >
    <Employee name="Amit" >
        <address>My address</address>
     </Employee>
     <issued-items>
        <item code="111" type="CD" label=" music" />
        <item code="222" type="DVD" label=" video"/>
     </issued-items>
</Employee-detail>


import java.io.*;

import org.xml.sax.*;

import org.xml.sax.helpers.DefaultHandler;

import org.xml.sax.helpers.XMLReaderFactory;

import org.xml.sax.Locator;



public class WorkingSAXParserLocator extends DefaultHandler {

  private Locator locator;

  public static void main(String[] args) {

    try {

      BufferedReader bf = new BufferedReader(new InputStreamReader(System.in));

      System.out.print("Enter xml file name: ");

      String xmlFile = bf.readLine();

      File file = new File(xmlFile);

      if (file.exists()){

        XMLReader parser = XMLReaderFactory.createXMLReader();

        DefaultHandler handler = new WorkingSAXParserLocator();   

        parser.setContentHandler(handler);

        //parse xml file

        parser.parse(xmlFile);

      }

      else{

        System.out.println("File not found!");

      }

    }

    catch (Exception e) {

      System.err.println(e);

    }

  }

  public void setDocumentLocator(Locator locator) {

    this.locator = locator;

  }

  //All methods positions

  private void printLocation(String location) { 

    int line = locator.getLineNumber();

    int column = locator.getColumnNumber();

    System.out.println(location + "  Line no: " + line + 

                                                  
"\tColumn no: " + column);

  }

  //Document start

  public void startDocument() { 

    printLocation("startDocument() method called at");

  }

  //Document end

  public void endDocument() { 

    printLocation("endDocument() method called at");

  }

  //Element start

  public void startElement(String namespaceURI, String localName, 

    String qualifiedName, Attributes atts) {

    printLocation("startElement() method called at ");

  }

  //Element end

  public void endElement(String namespaceURI, String localName, 

    String qualifiedName) {

    printLocation("endElement() method called at \t");

  }

  //characters

  public void characters(char[] text, int start, int length) {

    printLocation("characters() method called at \t"); 

  }

}

Output of this program:

C:\vinod\xml\sax1>javac WorkingSAXParserLocator.java

C:\vinod\xml\sax1>java WorkingSAXParserLocator
Enter xml file name: sample.xml
startDocument() method called at Line no: 1    Column no: 1
startElement() method called at     Line no: 1    Column no: 19
characters() method called at        Line no: 2    Column no: 2
startElement() method called at     Line no: 2    Column no: 25
characters() method called at        Line no: 3    Column no: 3
startElement() method called at     Line no: 3    Column no: 12
characters() method called at        Line no: 3    Column no: 22
endElement() method called at      Line no: 3    Column no: 32
characters() method called at        Line no: 4    Column no: 2
endElement() method called at      Line no: 4    Column no: 13
characters() method called at        Line no: 5    Column no: 2
startElement() method called at     Line no: 5    Column no: 16
characters() method called at        Line no: 5    Column no: 17
characters() method called at        Line no: 6    Column no: 3
startElement() method called at     Line no: 6    Column no: 47
endElement() method called at      Line no: 6    Column no: 47
characters() method called at        Line no: 7    Column no: 3
startElement() method called at     Line no: 7    Column no: 47
endElement() method called at      Line no: 7    Column no: 47
characters() method called at        Line no: 8    Column no: 2
endElement() method called at      Line no: 8    Column no: 17
characters() method called at        Line no: 9    Column no: 1
endElement() method called at      Line no: 9    Column no: 19
endDocument() method called at   Line no: 9    Column no: 19