Java and XML
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This document provides an overview of Java and XML processing using DOM, SAX, and JDOM. It outlines the key components and approaches for each, including parsing XML files into a DOM or SAX event model, traversing nodes and elements, and accessing attributes and content. JDOM is presented as an alternative Java DOM that supports Java collections and provides additional convenience methods for working with XML content.
![The Handler class
class Handler extends DefaultHandler {
// SAX calls this method when it encounters a start tag
public void startElement(String namespaceURI,
String localName,
String qualifiedName,
Attributes attributes) throws SAXException {
System.out.println("startElement: " + qualifiedName);
}
// SAX calls this method to pass in character data
public void characters(char ch[], int start, int length)
throws SAXException {
System.out.println("characters: "" +
new String(ch, start, length) + """);
}
// SAX call this method when it encounters an end tag
public void endElement(String namespaceURI,
String localName,
String qualifiedName) throws SAXException {
System.out.println("endElement: /" + qualifiedName);
}
}
20/01/2009
23](https://image.slidesharecdn.com/java-20and-20xml-131102171403-phpapp01/85/Java-and-XML-23-320.jpg)
Java and XML
- 1. Java and XML (DOM, SAX, JDOM) Raji GHAWI 20/01/2009
- 4. <inventory> <book year="2000"> <title>Snow Crash</title> <author>Neal Stephenson</author> <publisher>Spectra</publisher> <isbn>0553380958</isbn> <price>14.95</price> </book> <book year="2005"> <title>Burning Tower</title> <author>Larry Niven</author> <author>Jerry Pournelle</author> <publisher>Pocket</publisher> <isbn>0743416910</isbn> <price>5.99</price> </book> <book year="1995"> <title>Zodiac</title> <author>Neal Stephenson</author> <publisher>Spectra</publisher> <isbn>0553573862</isbn> <price>7.50</price> </book> <!-- more books... --> </inventory> 20/01/2009 4
- 5. Import required packages import javax.xml.parsers.*; import org.w3c.dom.*; 20/01/2009 5
- 6. Create the parser DOM parser factory try { DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance(); DocumentBuilder builder = factory.newDocumentBuilder(); // .... } catch (Exception e) { e.printStackTrace(System.out); } DOM parser 20/01/2009 IOException ParserConfigurationException SAXException 6
- 7. Parse an XML file Document document = builder.parse("../inventory.xml"); the entire XML file (as a tree) (the Document Object Model) 20/01/2009 7
- 8. Root element the root element Element root = document.getDocumentElement(); System.out.println(root.getTagName()); 20/01/2009 8
- 9. Nodes Node Text Element may have children Attr leaves Operations on Nodes Element Text Attr getNodeName() tag name "#text" name of attribute getNodeValue() null text contents value of attribute getNodeType() ELEMENT_NODE TEXT_NODE ATTRIBUTE_NODE getAttributes() NamedNodeMap null null 20/01/2009 9
- 10. Distinguishing Node types switch(node.getNodeType()) { case Node.ELEMENT_NODE: Element element = (Element)node; ...; break; case Node.TEXT_NODE: Text text = (Text)node; ... break; case Node.ATTRIBUTE_NODE: Attr attr = (Attr)node; ... break; default: ... } 20/01/2009 10
- 12. Travel through children nodes if (element.hasChildNodes()) { Node child = element.getFirstChild(); while (child != null) { // .... child = child.getNextSibling(); } } 20/01/2009 12
- 13. Operations for Elements String getTagName() boolean hasAttribute(String name) String getAttribute(String name) boolean hasAttributes() NamedNodeMap getAttributes() 20/01/2009 13
- 14. NamedNodeMap Node getNamedItem(String name) int getLength() Node item(int index) NamedNodeMap map = element.getAttributes(); for (int i = 0; i < map.getLength(); i++) { Attr attr = (Attr) map.item(i); System.out.println(attr.getNodeName() + "='"+ attr.getNodeValue()+"'"); } 20/01/2009 14
- 15. Operations on Texts String getData() int getLength() String substringData(int offset, int count) 20/01/2009 15
- 16. Operations on Attrs String getName() Element getOwnerElement() String getValue() 20/01/2009 16
- 17. 2. SAX Simple API for XML
- 18. Import required packages import javax.xml.parsers.*; import org.xml.sax.*; import org.xml.sax.helpers.*; 20/01/2009 18
- 19. Create the parser // Create a parser factory SAXParserFactory factory = SAXParserFactory.newInstance(); // Tell factory that the parser must understand namespaces factory.setNamespaceAware(true); try { // Make the parser SAXParser saxParser = factory.newSAXParser(); XMLReader parser = saxParser.getXMLReader(); } catch(Exception e){ e.printStackTrace(); } 20/01/2009 IOException ParserConfigurationException SAXException 19
- 20. Parse an XML file // Create a handler Handler handler = new Handler(); // Tell the parser to use this handler parser.setContentHandler(handler); // Finally, read and parse the document parser.parse("./inventory.xml"); 20/01/2009 20
- 21. SAX handlers A callback handler for SAX must implement four interfaces: interface ContentHandler interface DTDHandler interface EntityResolver interface ErrorHandler It is easier to use an adapter class 20/01/2009 21
- 22. Class DefaultHandler DefaultHandler is in package org.xml.sax.helpers DefaultHandler implements ContentHandler, DTDHandler, EntityResolver, and ErrorHandler DefaultHandler is an adapter class Provides empty methods for every method declared in each of the four interfaces To use this class, extend it and override the methods that are important to your application 20/01/2009 22
- 23. The Handler class class Handler extends DefaultHandler { // SAX calls this method when it encounters a start tag public void startElement(String namespaceURI, String localName, String qualifiedName, Attributes attributes) throws SAXException { System.out.println("startElement: " + qualifiedName); } // SAX calls this method to pass in character data public void characters(char ch[], int start, int length) throws SAXException { System.out.println("characters: "" + new String(ch, start, length) + """); } // SAX call this method when it encounters an end tag public void endElement(String namespaceURI, String localName, String qualifiedName) throws SAXException { System.out.println("endElement: /" + qualifiedName); } } 20/01/2009 23
- 24. <inventory> <book year="2000"> <title>Snow Crash</title> <author>Neal Stephenson</author> <publisher>Spectra</publisher> <isbn>0553380958</isbn> <price>14.95</price> </book> <book year="2005"> <title>Burning Tower</title> <author>Larry Niven</author> <author>Jerry Pournelle</author> <publisher>Pocket</publisher> <isbn>0743416910</isbn> <price>5.99</price> </book> <book year="1995"> <title>Zodiac</title> <author>Neal Stephenson</author> <publisher>Spectra</publisher> <isbn>0553573862</isbn> <price>7.50</price> </book> <!-- more books... --> </inventory> 20/01/2009 startElement: inventory characters: " " startElement: book characters: " " startElement: title characters: "Snow Crash" endElement: /title characters: " " startElement: author characters: "Neal Stephenson" endElement: /author characters: " " startElement: publisher characters: "Spectra" endElement: /publisher characters: " ... " endElement: /book ... endElement: /inventory 24
- 25. Attributes getLength() getLocalName(index) getQName(index) getValue(index) getType(index) int getIndex(String qualifiedName) int getIndex(String uri, String localName) String getValue(String qualifiedName) String getValue(String uri, String localName) 20/01/2009 25
- 26. Attributes public void startElement(String namespaceURI, String localName, String qualifiedName, Attributes attributes) throws SAXException { // .... for (int i = 0; i < attributes.getLength(); i++) { String attName = attributes.getQName(i); String attValue = attributes.getValue(i); System.out.println(attName+"='"+attValue+"'"); } // .... } 20/01/2009 26
- 27. 3. JDOM Java DOM
- 29. Create the parser try { SAXBuilder builder = new SAXBuilder(); // .... } catch (IOException ioe) { ioe.printStackTrace(); } catch (JDOMException je) { je.printStackTrace(); } 20/01/2009 29
- 30. Parse an XML file Document document = builder.build("../inventory.xml"); 20/01/2009 30
- 31. Root element Element root = document.getRootElement(); System.out.println(root.getName()); 20/01/2009 31
- 32. Print out the document XMLOutputter outputter = new XMLOutputter(); outputter.output(document, System.out); StringWriter sw = new StringWriter(); XMLOutputter outputter = new XMLOutputter(); outputter.output(document, sw); String xml = sw.toString(); Advantage 1: 20/01/2009 Output facility 32
- 33. Get children • Get all direct children List allChildren = element.getChildren(); • Get all direct children with a given name List namedChildren = element.getChildren("book"); • Get the first child with a given name Element child = element.getChild("book"); Advantage 2: 20/01/2009 supports Java Collections 33
- 34. Travel through children nodes List children = element.getChildren(); for (int i = 0; i < children.size(); i++) { Element elem = (Element) children.get(i); // .... } 20/01/2009 34
- 35. Get attributes • Get all attributes List attrs = element.getAttributes(); for (int i = 0; i < attrs.size(); i++) Attribute attr = (Attribute) attrs.get(i); System.out.println(attr.getName()+" = "+attr.getValue()); } • Get an attribute with a given name Attribute attr = element.getAttribute("year"); • Get an attribute value with a given name String value = element.getAttributeValue("year"); 20/01/2009 35
- 36. Reading Element Content • The text content is directly available String content = element.getText(); • Remove extra whitespace String content = element.getTextTrim(); 20/01/2009 36
- 37. Mixed Content • Sometimes an element may contain comments, text content, and children <table> <!-- Some comment --> Some text <tr>Some child</tr> </table> String text = table.getTextTrim(); Element tr = table.getChild("tr"); 20/01/2009 37
- 38. Mixed Content List mixedContent = table.getContent(); Iterator iter = mixedContent.iterator(); while (iter.hasNext()) { Object obj = iter.next(); if (obj instanceof Comment) { System.out.println("Comment: " + obj); } else if (obj instanceof String) { System.out.println("String: " + obj); } else if (obj instanceof Element) { System.out.println("Element: " + ((Element)obj).getName()); } } 20/01/2009 38
- 39. References Processing XML with Java; Elliotte Rusty Harold http://cafeconleche.org/books/xmljava/chapters/index.html 20/01/2009 39