XML - Polimi

XML EXERCISES
Sam Guinea
[email protected]
http://servicetechnologies.wordpress.com/
SAX VS DOM
SAX
•  Simple API for XML
•  Event-based sequential access parser API
•  There is no formal definition
•  Only a JAVA implementation that is normative
•  Documents are parsed state-dependently
SAX Parsers
•  A SAX Parser functions as a stream parser
•  With an event-driven API
•  SAX parsing is unidirectional
•  We define callback methods for the events
•  SAX events:
•  XML Text nodes
•  XML Element Starts and Ends
•  XML Processing Instructions
•  XML Comments
SAX Benefits vs Drawbacks
•  Memory Usage is negligible
•  Minimum memory is proportional to the maximum depth
of the XML file
•  Maximum data involved in a single XML event
•  Fastest kind of parsing for indexing, conversion,
formatting, etc.
•  Makes it hard to do XML validation and queries (Xpath)
DOM
•  Document Object Model
•  Cross-platform and language-independent
•  A document gains an object-based representation in
memory
•  Nodes are accessed through object methods
•  Origin tied to browser wars
•  Fundamental piece of software for managing pages
•  Used a lot in Java Web service technology stack
DOM Benefits vs Drawbacks
•  Makes it easy to manage XML files
•  Validation is simple
•  Possible to query the document
•  Can be slow to build the tree-like representation
•  Occupies a lot of memory
•  Can be made more efficient through persistency
Let’s see some Java code…
•  SAX
•  How to read an XML file
•  DOM
•  How to read an XML file
•  How to modify an XML file
•  How to create an XML file
•  How to count XML elements
JAXB
JAXB
•  Java Architecture for XML Binding.
•  Provides a fast and convenient way to bind between XML
schemas and Java representations.
•  Used to:
•  unmarshall XML instance document into Java content trees
•  marshall Java content trees into XML instance documents.
•  generate XML schemas from Java objects.
JAXB Binding Process
•  Compiling classes.
•  Unmarshalling.
•  Generating content tree of data
objects instantiated from the
generated JAXB classes.
•  Validate both source XML
documents and processed
content.
•  Process content.
•  Marshalling.
Representing XML Content
•  Grouping the generated classes in packages.
•  A package comprises:
•  A Java class name is derived from the element name.
•  An ObjectFactory class used to return instances of a bound Java
class.
•  Schema 2 Java
•  xsd:string à java.lang.String
•  xsd:int à int
•  xsd:dateTime à javax.xml.datatype.XMLGregorianCalendar
•  xsd:anySimpleType à java.lang.Object
@XmlRootElement
@XmlRootElement( name="doc" )
public class Document {
@XmlElement
protected Foo foo;
// ...
}
<?xml version="1.0" encoding="UTF-8"?>
<doc>
<foo>...</foo>
</doc>
<?xml version="1.0" encoding="UTF-8"?>
<xsd:complexType name="Foo">
...
</xsd:complexType>
<xsd:complexType name="Document">
<xsd:sequence>
<xsd:element name="foo" type="Foo"/>
</xsd:sequence>
</xsd:complexType>
<xsd:element name="doc" type="Document"/>
@XmlType
This annotation adds information that would be available from a schema type, but isn't implied by a
Java class declaration. The annotation has several attributes:
- The attribute name provides the XML schema name if you don't want to use the class name.
- The namespace attribute provides the name of the target namespace.
- The string array value defined by propOrder establishes an ordering of the sub-elements
@XmlRootElement
@XmlType( propOrder={ "title", "items", "cluster" } )
public class Document {
...
}
@XmlSchema
This annotation can only be used with a package. It defines parameters that are derived from the
xsd:schema element
@javax.xml.bind.annotation.XmlSchema(
namespace = "http://www.laune.at/hospital",
elementFormDefault = javax.xml.bind.annotation.XmlNsForm.QUALIFIED)
package hospital;
<xs:schema elementFormDefault="qualified"
targetNamespace="http://www.laune.at/hospital"
xmlns:tns="http://www.laune.at/hospital"
xmlns:xs="http://www.w3.org/2001/XMLSchema"
version="1.0" >
@XmlAccessorType
If JAXB binds a class to XML, then, by default, all public members will be bound, i.e., public getter and
setter pairs, or public fields. Any protected, package-visible or private member is bound if it is
annotated with a suitable annotation such as XmlElement or XmlAttribute. You have several
possibilities to influence this default behaviour.
XmlAccessType.FIELD
XmlAccessType. PROPERTY
@XmlElement and @XmlAttribute
@XmlElement(name = "Preamble", required = true)
protected PreambleType preamble;
@XmlElement(name = "Workplace", required = true)
protected List<SysWorkplaceType> workplace;
<xsd:sequence>
<xsd:element name="Preamble" type="com:PreambleType"/>
<xsd:element name="Workplace" type="SysWorkplaceType"
minOccurs="1" maxOccurs="unbounded"/>
</xsd:sequence>
@XmlAttribute
final static int answer = 42;
@XmlValue
public class Price {
private BigDecimal amount;
public Price(){}
@XmlElement
public BigDecimal getAmount(){
return amount;
}
public void setAmount( BigDecimal value ){
this.amount = value;
}
}
<xs:complexType name="price">
<xs:sequence>
<xs:element name="amount" type="xs:decimal" minOccurs="0"/>
</xs:sequence>
</xs:complexType>
<price>
<amount>123.45</amount>
</price>
@XmlValue
public class Price {
// ...
@XmlValue
public BigDecimal getAmount(){
return amount;
}
// ...
}
<xs:simpleType name="price">
<xs:restriction base="xs:decimal"/>
</xs:simpleType>
<price>123.45</price>
Examples
•  Unmarshal Read
•  how to unmarshal an XML document into a Java content tree and
access the data contained within it.
•  How to modify the data and push it back to XML
•  Adding XSD Validation
•  how to enable validation during unmarshalling.
•  Creating a model
•  Model creation and generation of an XSD
•  Personalization of model mapping
Schema Validation
boolean handleEvent(ValidationEvent event)
Parameters:
event - the encapsulated validation event information. It is a provider error if this
parameter is null.
Returns:
true if the JAXB Provider should attempt to continue the current unmarshal,
validate, or marshal operation after handling this warning/error, false if the
provider should terminate the current operation with the appropriate.
Throws:
IllegalArgumentException - if the event object is null.
XPATH IN JAVA
JAXEN
•  Open source XPath library written in Java
•  http://jaxen.codehaus.org/
•  Chosen by Sun for
•  JSP Standard Tag Library
•  Java Web services Development Pack 1.0 and 1.1
•  Java API for XML Messaging
•  Means we can use it with SOAP messages
Only three steps
•  Construct an XPath object by passing a String containing
an XPath expression
•  public DOMXPath(String expression)
throws JaxenException;
•  Set the namespace bindings by calling
•  public void addNamespace(String prefix, String uri)
throws JaxenException;
•  Evaluate the expression (methods vary depending on
desired result type)
•  public List selectNodes(Object context)
throws JaxenException;
LAB EXERCISES
Esercizio parte 1
•  Mediante annotazioni JAXB creare l’XML Schema per la
gestione di una libreria (bookstore.xsd)
•  Bookstore
•  Book
•  Title
•  Author
•  Date
•  ISBN
•  Publisher
•  Cost
Esercizio parte 2
•  Usare lo schema “bookstore.xsd” definito al punto
precedente per generare le classi del modello della
libreria
•  Scrivere un programma che crea una libreria di 10 libri e
lo serializza e salva in un file XML chiamato “books.xml”
Esercizio parte 3
•  Scrivere un programma che carica il contenuto del file
“books.xml” in memoria sotto forma di DOM
•  Usare Xpath per rispondere alle seguenti query
•  Restituire tutti gli autori
•  Restituire tutti i libri scritti da un autore a vostra scelta
•  Restituire tutti i libri ce hanno un costo superiore a 10 euro
•  Restituire i nomi degli editori che pubblicano libri che costano più di
10 euro