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A Gentle Introduction to xml

Introducing SAX
With answers

SAX is a "Simple API for XML" - an API is "Application Programmer Interface". SAX allows us to write programs that process XML documents a bit at a time. SAX programs may be more difficult to follow than DOM programs - but they will perform well with the large XML documents that leave DOM thrashing.

Documentation

Question 1: startElement and startDocument and endDocument

The NodeCounter class is an implementation of ContentHandler. We override three methods, startDocument, startElement endDocument. Each of these methods gets called when the parser reaches the corresponding part of the document.

<?xml version="1.0" encoding="UTF-8" ?>
<stock andrew="was here">
  <item price="50" legend="Pr-Burger" BarCode="E1" />
  <item price="15" legend="Crisp S+V" BarCode="E5" />
  <item price="15" legend="Crisp C+O" BarCode="E6" />
  <item price="50" legend="Flat Cola" BarCode="E7" />
</stock>

Examine the program and try it out. The output should give the total number of nodes in the input file.
Include the line System.out.println(atts.getValue("BarCode")); in the startElement method. This should display the BarCode value for each node as it is processed. Notice value displayed for the stock node which has no such attribute.

Content Handler

import org.xml.sax.*;

public class NodeCounter implements ContentHandler {

int nodeCount;

public void startDocument() throws SAXException
  {
    nodeCount=0;
  }

public void startElement(String namespaceURI, String localName,
   String qualifiedName, Attributes atts) throws SAXException
  {
    nodeCount++;
    System.out.println(atts.getValue("BarCode")); 
  }

public void endDocument() throws SAXException
  {
    System.out.println("Number of nodes: " + nodeCount);
  }

// Do-nothing methods
  public void setDocumentLocator(Locator l) {}
  public void startPrefixMapping(String p, String u)
   throws SAXException {}
  public void endPrefixMapping(String p) throws SAXException {}
  public void skippedEntity(String n) throws SAXException {}
  public void processingInstruction(String t, String d)
   throws SAXException {}
  public void characters(char[] t, int s, int l)
   throws SAXException {}
  public void ignorableWhitespace(char[] t, int s, int l)
   throws SAXException{}
  public void endElement(String namespaceURI, String localName,
   String qualifiedName) throws SAXException {}
}

Java SAX

Question 2: localName

The parameter localName gives the name of the ndoe - with no namespace information.

Change the code so that it only counts and prints nodes if the localName is equal to "item". There should be 4 of them.
Change the code so that it prints item number, legend and price on one line for each item. The output should look like:
```
1 Pr-Burger 50
2 Crisp S+V 15
3 Crisp C+O 15
4 Flat Cola 50
```

Content Handler

import org.xml.sax.*;

public class NodeCounter implements ContentHandler {

int nodeCount=0;

public void startElement(String namespaceURI, String localName,
   String qualifiedName, Attributes atts) throws SAXException
  {
    if (localName.equals("item")){
      nodeCount++;
      System.out.println(nodeCount+" "+
           atts.getValue("legend")+" "+
           atts.getValue("price"));
     }
  }

A Gentle Introduction to xml

Introducing SAXWith answers

Documentation

Question 1: startElement and startDocument and endDocument

Content Handler

Java SAX

Question 2: localName

Content Handler

Java SAX

Introducing SAX
With answers