Parsing XML wit SAX parser

Android provides org.xml.sax package that has that provides the event-driven SAX parser.
to parse the previous response with SAX parser, we have to create a class extending DefaultHandler and override the following methods:

1. startDocument(): invoked when the xml document is open, there we can initialize any member variables.
2. startElement(String uri, String localName, String qName, Attributes attributes): invoked when the parser encounters a xml node, here we can initialize specific instances of our person object.
3. endElement(String uri, String localName, String Name): invoked when the parser reaches the closing of a xml tag. here the element value would have been completely read.
4. characters(char[] ch, int start, int length): this method is called when the parser reads characters of a node value.

we want to parse this xml response:

<?xml version="1.0"?>
<person>
 <firstname>Jack</firstname>
 <lastname>smith</lastname>
 <age>28</age>
</person>

so our parsing class will be like this:

/**
 * SAX parser to parse persons response
 */
 public class PersonParser extends DefaultHandler
 {

 // arraylist to store person objects
 ArrayList persons;
 // temporary person object
 Person tempPerson;
 // string builder acts as a buffer
 StringBuilder builder;

 /**
 * Initialize the arraylist
 * @throws SAXException
 */
 @Override
 public void startDocument() throws SAXException {
 pesons=new ArrayList();

 }

 /**
 * Initialize the temp person object which will hold the parsed in//fo
 * and the string builder that will store the read characters
 * @param uri
 * @param localName
 * @param qName
 * @param attributes
 * @throws SAXException
 */
 @Override
 public void startElement(String uri, String localName, String qName,
 Attributes attributes) throws SAXException {

 if(localName.equalsIgnoreCase.equals("person")){
 tempPerson=new Person();
 builder=new StringBuilder();
 }

 }
 /**
 * Finished reading the person tag, add it to arraylist
 * @param uri
 * @param localName
 * @param qName
 * @throws SAXException
 */
 @Override
 public void endElement(String uri, String localName, String qName)
 throws SAXException {
 // finished reading a person, add it to the arraylist
 if(localName.toLowerCase().equals("person"))
 {
 this.persons.add(tempPerson);
 }
 // finished reading "firstname" tag assign it to the temp person
 else if(localName.toLowerCase().equals("firstname")){
 tempPerson.firstName=builder.toString();
 }
 // finished reading "lastname" tag assign it to the temp person
 else if(localName.toLowerCase().equals("lastname")){
 tempPerson.lastName=builder.toString();
 }
 // finished reading "age" tag assign it to the temp person
 else if(localName.toLowerCase().equals("age")){
 tempPerson.age=Integer.parseInt(builder.toString());
 }
 }

 /**
 * Read the value of each tag
 * @param ch
 * @param start
 * @param length
 * @throws SAXException
 */
 @Override
 public void characters(char[] ch, int start, int length)
 throws SAXException {
 // read the characters and append them to the buffer
 String tempString=new String(ch, start, length);
 builder.append(tempString);
 }
 }

the code is pretty easy, the parser iterates over each node, you check the current node name and take an action.

then we call the parser like this:

public ArrayList getPersons(final String response) throws ParserConfigurationException, SAXException, IOException
 {
 BufferedReader br=new BufferedReader(new StringReader(response));
 InputSource is=new InputSource(br);
 PersonParser parser=new PersonParser();
 SAXParserFactory factory=SAXParserFactory.newInstance();
 SAXParser sp=factory.newSAXParser();
 XMLReader reader=sp.getXMLReader();
 reader.setContentHandler(parser);
 reader.parse(is);
 ArrayList persons=parser.persons;

 return persons;

 }

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