Parsing XML using JSR 172
Article Metadata
The intention of this code snippet is to give an idea about how to parse an xml file using JSR 172.
- This example receives an URL of an XML file
- Opens an HttpConnection to the file to get the InputStream
- Uses the Input Stream as a means to create a SAXParser
When the SAXParser is successfully created, the application will use the callbacks to track the whole document.
import java.io.IOException;
import java.io.InputStream;
import javax.microedition.io.Connector;
import javax.microedition.io.HttpConnection;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.Attributes;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;
/**
*Class in Charge of http connectivity and xml parsing
*/
public class XMLParser extends DefaultHandler implements Runnable {
private String URL;
private HttpConnection http;
StringBuffer log = new StringBuffer();
/**
* Starts connecting to the given URL to fetch the XML file.
* The connection is started in a separate thread
* @param URL
*/
public void connect(String URL) {
this.URL = URL;
Thread thread = new Thread(this);
thread.start();
}
/**
* Opens the connection and fetches the xml file
*/
public void run() {
loadXML(getInputStream());
}
private InputStream getInputStream() {
InputStream input = null;
try {
http = (HttpConnection) Connector.open(URL);
// Getting the response code will open the connection,
int rc = http.getResponseCode();
if (rc == HttpConnection.HTTP_OK) {
String type = http.getType();
if (type.startsWith("text/xml")) {
input = http.openInputStream();
}
}
} catch (IOException ex) {
}
return input;
}
/**
* Starts parsing the received XML file using a SAXParser
*/
public void loadXML(InputStream input) {
SAXParser parser;
try {
SAXParserFactory factory =
SAXParserFactory.newInstance();
parser =
factory.newSAXParser();
InputSource fis = new InputSource(input);
parser.parse(fis, this);
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* Callback invoked when a start tag is loaded
* @param uri
* @param localName
* @param qName
* @param attributes
* @throws org.xml.sax.SAXException
*/
public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
}
/**
* Callback invoked when an end tag is found
* @param uri
* @param localName
* @param qName Nombre de la etiqueta
* @throws org.xml.sax.SAXException
*/
public void endElement(String uri, String localName, String qName)
throws SAXException {
}
/**
* Callback invoked when the tag contains a text.
* Text is saved according to the tag being analyzed
* as the callback does not pass any reference to the current tag
* a global variable currentTag is used to store the value.
* Data is saved in the current visit
* @param ch
* @param start
* @param length
* @throws org.xml.sax.SAXException
*/
public void characters(char[] ch, int start, int length) throws SAXException {
String chars = new String(ch, start, length).trim();
if (chars.length() > 0) {
}
}
}
24 Sep
2009
This article provides a fairly simple example of how to parse an XML file using JSR 172 (Web Service) API. The code example demonstrates how to read in an XML file via an HTTPConnection and parse this file using the web service API. The example demonstrates the use of the different classes within the API, without actually doing anything with the contents of the XML file (most of the methods for parsing the XML file are left blank).
In some respects, the simplicity of the code example could be criticised, because it doesn’t actually show how to do things like identify the current tag, retrieve an attribute or retrieve the contents of a tag containing text. However, other examples exist to show this functionality. This article is merely intended to show which objects to use to create a parser object and initiate the parsing process. Code to perform the actual parsing requires an illustrative example to be meaningful. The code example shows how a SAXParser object is created using the factory design pattern, with an instance being created using the newSAXParser() method of the SAXParserFactory class.
A useful follow up article would be to demonstrate how to use the methods such as startElement, endElement and characters to retrieve specific information from an XML file. These methods are generally used in conjunction with a stack data structure to process data in XML format.