1 dr alexiei dingli xml technologies sax and dom

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Dr Alexiei Dingli

XML Technologies

SAX and DOM

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• Simple API for XML

• Used to parse XML

• But does not create a default object

• It just fires events when it detects objects such as– open or close tags– PCDATA or CDATA– Comments– entities

What is SAX?

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• Imagine the following document:

<?xml version = "1.0"?>

<addressbook>

<person>

<lastname>Dingli</lastname>

<firstname>Alexiei</firstname>

<company>University of Malta</company>

<email>alexiei.dingli@um.edu.mt</email>

</person>

</addressbook>

Example

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1. Creating a custom object model (like Person and AddressBook classes)

2. Creating a SAX parser

3. Creating a DocumentHandler (to turn your XML document into instances of your custom object model).

SAX in 3 steps

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• Create both a person and an address book object

• Create its setters, getters and to xml methods

Custom Object Model (1)

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Custom Object Model

(2)

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Create a SAX

parser

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• Actually 4 Interfaces ...

– The Document Handler

– The Entity Resolver

– The DTD Handler

– The Error Handler

Create a Document Handler (1)

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Create a Document Handler (2)

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parser.setDocumentHandler( ... )

parser.setDTDHandler( ... )

parser.setErrorHandler( ... )

Setting the parser

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• Rather than implementing all the interfaces mentioned earlier

• Make use of org.xml.sax.helpers.DefaultHandler

• Which implements all the methods

• And you simply override what you want to use

• http://java.sun.com/j2se/1.4.2/docs/api/org/xml/sax/helpers/DefaultHandler.html

Handler Class

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SAX Handler

Example Handler

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• W3C standard

• Standard way of accessing and manipulating documents

• Divided into 3 parts

– Core DOM (access any structured document)

– XML DOM

– HTML DOM

• Presents element as a tree structure

DOM

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• A standard object model for XML

• A standard programming interface for XML

• Platform- and language-independent

• A W3C standard

• The XML DOM is a standard for how to get, change, add, or delete XML elements

XML DOM

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Everything in XML is a node

– The entire document is a document node– Every XML element is an element node– The text in the XML elements are text nodes– Every attribute is an attribute node– Comments are comment nodes

XML DOM rulez

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<bookstore>

<book category="web" cover="paperback">

<title lang="en">Learning XML</title>

<year>2008</year>

</book>

</bookstore>

• Bookstore is the root node

• It contains one book node

• A book node contains a title node and a year node

• Title contains a text node “Learning XML”

• 2008 is not the value of the year node but a text node inside the year node

Example

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• Any DOM object has a node tree where– In a node tree, the top node is called the root– Every node, except the root, has exactly one

parent node– A node can have any number of children– A leaf is a node with no children– Siblings are nodes with the same parent

The node tree

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text="<bookstore>"

text=text+"<book>";

text=text+"<title>Everyday Italian</title>";

text=text+"<author>John Smith</author>";

text=text+"<year>2008</year>";

text=text+"</book>";

text=text+"</bookstore>";

Creating the XML

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try //Internet Explorer

{

xmlDoc=new ActiveXObject("Microsoft.XMLDOM"); xmlDoc.async="false";

xmlDoc.loadXML(text);

} catch(e) {

try //Firefox, Mozilla, Opera, etc.

{

parser=new DOMParser(); xmlDoc=parser.parseFromString(text,"text/xml");

} catch(e) {

alert(e.message)

}

}

document.write("xmlDoc is loaded, ready for use");

Parsing the XML

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• x.getElementsByTagName(name) - get all elements with a specified tag name

• x.appendChild(node) - insert a child node to x

• x.removeChild(node) - remove a child node from x

XML DOM Methods

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• x.nodeName - the name of x

• x.nodeValue - the value of x

• x.parentNode - the parent node of x

• x.childNodes - the child nodes of x

• x.attributes - the attributes nodes of x

XML DOM properties

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document.write(xmlDoc.getElementsByTagName("title") [0].childNodes[0].nodeValue);

document.write("<br />");

document.write(xmlDoc.getElementsByTagName("author") [0].childNodes[0].nodeValue);

document.write("<br />");

document.write(xmlDoc.getElementsByTagName("year") [0].childNodes[0].nodeValue);

Examples

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1. By using the getElementsByTagName() method

2. By looping through (traversing) the nodes tree

3. By navigating the node tree, using the node relationships

Accessing nodes

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xmlDoc.getElementsByTagName("title") [0].childNodes[0].nodeValue;

Example 1

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x=xmlDoc.getElementsByTagName("title");

for ( i=0; i<x.length; i++) { document.write(x[i].childNodes[0].nodeValue); document.write("<br />");

}

Example 2

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x=xmlDoc.getElementsByTagName("book")[0].childNodes;

y=xmlDoc.getElementsByTagName("book")[0].firstChild;

for (i=0;i<x.length;i++) {

if (y.nodeType==1) {//Process only element_nodes (type 1)

document.write(y.nodeName + "<br />");

}

y=y.nextSibling;

}

Example 3

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• nodeName

• nodeValue

• nodeType

Node properties

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• nodeName is read-only

• nodeName of an element node is the same as the tag name

• nodeName of an attribute node is the attribute name

• nodeName of a text node is always #text

• nodeName of the document node is always #document

nodeName property

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• nodeValue for element nodes is undefined

• nodeValue for text nodes is the text itself

• nodeValue for attribute nodes is the attribute value

nodeValue property

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Node type NodeType

Element 1

Attribute 2

Text 3

Comment 8

Document 9

nodeType property

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x=xmlDoc.getElementsByTagName("book")[0].attributes;

document.write(x.getNamedItem("category").nodeValue);

Acessing node attributes

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// documentElement always represents the root node

x=xmlDoc.documentElement.childNodes;

for (i=0;i<x.length;i++) {

document.write(x[i].nodeName); document.write(": "); document.write(x[i].childNodes[0].nodeValue); document.write("<br />");

}

Traversing Example

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• parentNode

• childNodes

• firstChild

• lastChild

• nextSibling

• previousSibling

Navigating Nodes (1)

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Navigating Nodes (2)

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x=xmlDoc.getElementsByTagName("title")[0];

y=x.childNodes[0];

txt=y.nodeValue;

Result = the name of the book

Title node > Text node

Getting the node value

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x=xmlDoc.getElementsByTagName("title")[0].childNodes[0];

x.nodeValue="Easy Cooking";

Setting the node value

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y=xmlDoc.getElementsByTagName("book")[0];

xmlDoc.documentElement.removeChild(y);

Or

y.parentNode.removeChild(y);

Removing Nodes

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newel=xmlDoc.createElement("edition");

x=xmlDoc.getElementsByTagName("book")[0];

x.appendChild(newel);

Creating nodes

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newel=xmlDoc.createElement("edition");

newtext=xmlDoc.createTextNode("first");

newel.appendChild(newtext);

x=xmlDoc.getElementsByTagName("book")[0];

x.appendChild(newel);

Creating text nodes

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newCDATA=xmlDoc.createCDATASection("Special Offer & Book Sale");

x=xmlDoc.getElementsByTagName("book")[0];

x.appendChild(newCDATA);

Create CDATA nodes

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newComment=xmlDoc.createComment("Revised March 2008");

x=xmlDoc.getElementsByTagName("book")[0];

x.appendChild(newComment);

Create Comment Node

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x.appendChild(newNode)

x.insertBefore(newNode,y)

x.cloneNode(true) // add all attributes and children if true

x.insertData(offset,"Easy "); // add text

More additional methods

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x=xmlDoc.getElementsByTagName("title")[0].getAttributeNode("lang");

txt=x.nodeValue;

Getting attribute value

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newatt=xmlDoc.createAttribute("edition");

newatt.nodeValue="first";

x=xmlDoc.getElementsByTagName("title");

x[0].setAttributeNode(newatt);

Creating attributes

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x=xmlDoc.getElementsByTagName('book');

x[0].setAttribute("category","food");

Or

x=xmlDoc.getElementsByTagName("book")[0]

y=x.getAttributeNode("category");

y.nodeValue="food";

Setting the attribute value

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x=xmlDoc.getElementsByTagName("book");

x[0].removeAttribute("category");

Removing attributes

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• Given the following XML file

• How shall we display – Two buttons

• “Get CD info” and display the Titles and the Composer

• “Get CD info abridged” and display the Titles only

Exercise

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• The code

• What’s the result?

Answer (1)

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Answer (2)

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Questions?