The document discusses different data formats including JSON and XML. It provides information on parsing XML, including using DOM and SAX parsers to convert an XML document into a tree structure or sequence of events. Examples are given of representing XML data in Java objects using JAXB annotations and then marshalling and unmarshalling XML to and from those Java objects.

1. Data formats
Web Technology - 2ID60
28 November 2013
Katrien Verbert
Natasha Stash
George Fletcher

2. Plan for today
• Data formats:
• JSON
• XML
• Parsing XML
• Example RESTful service that exchanges XML data
• Mini-project
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3. Data formats
• JSON
• XML
• Parsing XML
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4. JSON
• JSON: JavaScript Object Notation.
• JSON is syntax for storing and exchanging text
information.
• JSON is smaller than XML, and faster and easier to
parse.
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5. JSON
Maps to two universal structures
1. An unordered collection of name value pairs:
{"firstName”:"Nicole”,"lastName": "Kidman”}
2. An ordered list of values
["Monday”, "Tuesday”, "Wednesday”]
Source: Theresa Velden
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6. JSON Syntax
http://www.json.org/
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7. JSON syntax
• An object is an unordered set of name/value pairs
•
•
•
•
The pairs are enclosed within braces, { }
There is a colon between the name and the value
Pairs are separated by commas
Example: { "firstName":"John" , "lastName":"Doe" }
• An array is an ordered collection of values
• The values are enclosed within brackets, [ ]
• Values are separated by commas
• Example: [ "html", xml", "css" ]

8. JSON example: de-constructed
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Source: Theresa Velden
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9. JSON example: de-constructed
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Source: Theresa Velden
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10. JSON example: de-constructed
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Source: Theresa Velden
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11. JSON example: de-constructed
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Source: Theresa Velden
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12. More information about JSON
• http://www.w3schools.com/json/default.asp
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13. Overview
• JSON
• XML
• parsing XML
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14. Introduction to XML
• Why is XML important?
• simple open non-proprietary widely accepted data
exchange format
• XML is like HTML but
• no fixed set of tags
− X = “extensible”
• no fixed semantics (c.q. representation) of tags
− representation determined by separate ‘style sheet’
− semantics determined by application
• no fixed structure
− user-defined schemas

15. XML: running example
<?xml version="1.0"?>
<Order>
<Date>2003/07/04</Date>
<CustomerId>123</CustomerId>
<CustomerName>Acme Alpha</CustomerName>
<Item>
<ItemId> 987</ItemId>
<ItemName>Coupler</ItemName>
<Quantity>5</Quantity>
</Item>
<Item>
<ItemId>654</ItemId>
<ItemName>Connector</ItemName>
<Quantity>3</Quantity>
</Item>
</Order>

16. Elements of an XML Document
• Global structure
• Mandatory first line
<?xml version ="1.0"?>
• A single root element
<order>
. . .
</order>
• Elements have a recursive structure
• Tags are chosen by author;
<item>, <itemId>, <itemName>
• Opening tag must have a matching closing tag
<item></item>, <a><b></b></a>

17. Elements of an XML Document
• The content of an element is a sequence of:
− Elements
<item> … </item>
− Text
Jan Vijs
− Processing Instructions
<! . . . !>
− Comments
<!– This is a comment --!>
• Empty elements can be abbreviated:
<item/> is shorthand for
<item></item>

18. Elements of an XML Document
• Elements can have attributes
<Title Value="Student List"/>
<PersonList Type="Student" Date="2004-12-12">
. . .
</Personlist>
Attribute_name = “Value”
Attribute name can only occur once
Value is always quoted text (even numbers)

19. Elements of an XML Document
• Text and elements can be freely mixed
<Course ID=“2ID45”>
The course <fullname>Database
Technology</fullname> is lectured
by <title>dr.</title>
<fname>George</fname>
<sname>Fletcher</sname>
</Course>
• The order between elements is considered important
• Order between attributes is not

20. Well-formedness
• We call an XML-document well-formed iff
• it has one root element;
• elements are properly nested;
• any attribute can only occur once in a given opening
tag and its value must be quoted.
• Check for instance at:
http://www.w3schools.com/xml/xml_validator.asp

21. Overview
• JSON
• XML
• parsing XML
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22. Parsing XML
• Goal
• Read XML files into data structures in programming
languages
• Possible strategies
• Parse into generic tree structure (DOM)
• Parse as sequence of events (SAX)
• Automatically parse to language-specific objects (JAXB)

23. DOM
• A DOM document is an object containing all the
information of an XML document
• It is composed of a tree (DOM tree) of nodes
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24. DOM parsers
Different types of nodes
Document node
Element node
Text node
Attribute node
Processing instruction node
…….

25. Example
Source: Theresa Velden
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26. Example DOM tree
Source: Theresa Velden
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27. Example DOM tree
Source: Theresa Velden
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28. DOM parsers

29. XML example
<?xml version="1.0"?>
<Order>
<Date>2003/07/04</Date>
<CustomerId>123</CustomerId>
<CustomerName>Acme Alpha</CustomerName>
<Item>
<ItemId> 987</ItemId>
<ItemName>Coupler</ItemName>
<Quantity>5</Quantity>
</Item>
<Item>
<ItemId>654</ItemId>
<ItemName>Connector</ItemName>
<Quantity>3</Quantity>
</Item>
</Order>

30. DOM tree example
Example code fragment:
Node order= doc.getFirstChild();
order
item
CustomerId
_123456789
item
CustomerId
_333445555
item
CustomerId
_999887777

31. DOM tree example
Example code fragment:
Node order= doc.getFirstChild();
NodeList items= order.getChildNodes();
order
item
CustomerId
_123456789
item
CustomerId
_333445555
item
CustomerId
_999887777

32. DOM tree example
Example code fragment:
NodeList items=
doc.getElementsByTagName("item")
order
item
CustomerId
_123456789
item
CustomerId
_333445555
item
CustomerId
_999887777

33. Main features of DOM parsers
• A DOM parser creates an internal structure in memory
which is a DOM document object
• Client applications get the information of the original
XML document by invoking methods on this Document
object or on other objects it contains
• DOM parser is tree-based

34. Parsing XML in Java
• Package javax.xml.parsers
• Provides classes allowing the processing of XML
documents.
• SAX (Simple API for XML)
• DOM (Document Object Model)

35. Example: order list
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<order>
<customerId>123</customerId>
<customerName>Katrien Verbert</customerName>
<date>12 February 2013</date>
<item>
<itemId>id1</itemId>
<itemName>Iphone 5</itemName>
<quantity>2</quantity>
</item>
<item>
<itemId>id2</itemId>
<itemName>Nokia Lumia 800</itemName>
<quantity>1</quantity>
</item>
</order>
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36. Representing objects in Java
public class Item {
String id;
String name;
String quantity;
public Item(String id, String name, String quantity) {
this.id = id;
this.name = name;
this.quantity = quantity;
}
public Item(){}
+ getters and setters
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37. Representing objects in Java
public class Order {
private String date;
private String customerId;
private String customerName;
private ArrayList<Item> items;
public Order(String date, String customerId, String customerName) {
this.date = date;
this.customerId = customerId;
this.customerName = customerName;
items=new ArrayList<Item>();
}
…
}
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38. DOM parser example
public void parse(String fileName) throws Exception{
DocumentBuilderFactory factory =
DocumentBuilderFactory.newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();
Document doc = builder.parse(fileName);
NodeList itemList = doc.getElementsByTagName("item");
for (int i = 0; i < itemList.getLength(); i++)
{
Node itemNode = itemList.item(i);
Item item=getItem(itemNode);
}
}
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39. DOM tree example
Example code fragment:
NodeList items=
doc.getElementsByTagName("item")
order
item
CustomerId
_123456789
item
CustomerId
_333445555
item
CustomerId
_999887777

40. DOM parser example
public Item getItem (Node n){
NodeList itemElements = n.getChildNodes();
Item item = new Item();
for (int j = 0; j < itemElements.getLength(); j++)
{
Node node=itemElements.item(j);
if (node.getNodeName().equalsIgnoreCase("itemId"))
item.setId(node.getTextContent());
else if (node.getNodeName().equalsIgnoreCase("itemName"))
item.setName(node.getTextContent());
else if (node.getNodeName().equalsIgnoreCase("quantity"))
item.setQuantity(node.getTextContent());
}
return item;
}
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41. JAXB
• JAXB: Java API for XML Bindings
• Defines an API for automatically representing XML
schema as collections of Java classes.

42. Annotations markup
•
•
•
•
@XmlAttribute to designate a field as an attribute
@XmlRootElement to designate the document root element.
@XmlElement to designate a field as a node element
@XmlElementWrapper to specify the element that encloses a
repeating series of elements
• Note that you should specify only the getter method as
@XmlAttribute or @XmlElement.
• Jaxb oddly treats both the field and the getter method as
independent entities

43. Order example
import javax.xml.bind.annotation.*;
@XmlRootElement
public class Item {
@XmlElement
private String itemId;
@XmlElement
private String ItemName;
@XmlElement
private int quantity;
public Item() {
}
}
}

44. Order example
import javax.xml.bind.annotation.*;
import java.util.*;
@XmlRootElement
public class Order {
@XmlElement
private String date;
@XmlElement
private String customerId;
@XmlElement
private String customerName;
@XmlElement
private List<Item> items;
public Order() {
this.items=new ArrayList<Item>();
}

45. Marshalling
• marshalling
• the process of producing an XML document from Java objects
• unmarshalling
• the process of producing a content tree from an XML document
• JAXB only allows you to unmarshal valid XML documents
• JAXB only allows you to marshal valid content trees into XML

46. Marshalling example
public String toXmlString(){
try{
JAXBContext context=JAXBContext.newInstance(Order.class);
Marshaller m = context.createMarshaller();
m.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, Boolean.TRUE);
ByteArrayOutputStream b=new ByteArrayOutputStream();
m.marshal(this,b);
return b.toString();
}catch (Exception e){
e.printStackTrace();
return null;
}
}

47. Unmarshalling example
public Order fromXmlString(String s){
try{
JAXBContext jaxbContext = JAXBContext.newInstance(Order.class);
Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
Order order = (Order) jaxbUnmarshaller.unmarshal(new StreamSource( new
StringReader(s)));
return order;
}catch (Exception e){
e.printStackTrace();
return null;
}
}

48. Test transformation
public static void main(String args[]){
Order o=new Order("1 March 2013", "123", "Katrien");
o.getItems().add(new Item("1", "iPhone 5", 2));
o.getItems().add(new Item("2", "Nokia Lumia 800", 2));
System.out.println(o.toXmlString());
}

49. Output
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<order>
<customerId>123</customerId>
<customerName>Katrien Verbert</customerName>
<date>12 February 2013</date>
<items>
<itemId>id1</itemId>
<ItemName>Iphone 5</ItemName>
<quantity>2</quantity>
</items>
<items>
<itemId>id2</itemId>
<ItemName>Nokia Lumia 800</ItemName>
<quantity>1</quantity>
</items>
</order>

50. k.verbert@tue.nl
n.v.stash@tue.nl
g.h.l.fletcher@tue.nl