Data formats

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
PAGE 4 28/11/13

3. Data formats
• JSON
• XML
• Parsing XML
PAGE 5 28/11/13

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.
PAGE 6 27/11/13

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”]

PAGE 7 27/11/13 Source: Theresa Velden

6. JSON Syntax
PAGE 8 27/11/13
http://www.json.org/

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
PAGE 10
27/11/13
Source: Theresa Velden

9. JSON example: de-constructed
PAGE 11
27/11/13
Source: Theresa Velden

10. JSON example: de-constructed
PAGE 12
27/11/13
Source: Theresa Velden

11. JSON example: de-constructed
Source: Theresa Velden PAGE 13
27/11/13

12. More information about JSON
• http://www.w3schools.com/json/default.asp
PAGE 14 27/11/13

13. Overview
• JSON
• XML
• parsing XML
PAGE 15 27/11/13

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
PAGE 23 27/11/13

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
PAGE 25 27/11/13

24. DOM parsers
Different types of nodes
Document node
Element node
Text node
Attribute node
Processing instruction node
…….

25. Example
PAGE 27 27/11/13 Source: Theresa Velden

26. Example DOM tree
PAGE 28 27/11/13 Source: Theresa Velden

27. Example DOM tree
PAGE 29 27/11/13 Source: Theresa Velden

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

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

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

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>
PAGE 37 27/11/13

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
PAGE 38 27/11/13

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>();
}
…
}

PAGE 39 27/11/13

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);
}

}
PAGE 40 27/11/13

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

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;
}
PAGE 42 27/11/13

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. [email protected]
[email protected]
[email protected]