Linguaggi Speciali di Programmazione 1

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Linguaggi Speciali di Programmazione 1

• Ing. Marco Scotto (scotto_at_dist.unige.it)

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Outline

• Web Services vs. CORBA
• Web Services or CORBA?
• WS-CORBA interoperation
• Java XML

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Web Services vs. CORBA (1/4)
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Web Services vs. CORBA (2/4)
Server Side Usage

• Web Services
• define the service as interface in WSDL
• compile the WSDL to generate the stub and the
  skeleton
• implement the service and associate it with the
  skeleton (implementation dependent)
• publish the service with UDDI for use by clients

• CORBA
• define the service as interface in IDL
• compile the IDL to generate the stub and the
  skeleton
• implement the service and associate it with the
  skeleton via the portable object adapter (POA)
• publish the service with a Naming Service for use
  by clients

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Web Services vs. CORBA (3/4)
Client Side Usage

• Web Services
• contact UDDI for the desired service and retrieve
  the URL
• invoke operations on the URL using the generated
  stub from the WSDL
• process reply

• CORBA
• contact the Naming Service for the desired
  service and retrieve the object reference
• invoke operations on the object reference using
  the IDL-compiler generated stub
• process reply

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Web Services vs. CORBA (4/4)
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Web Services or CORBA? (1/3)

• Web Interface
• WS are the best XSLT can easily convert SOAP
  messages into HTML (CORBA requires more work)
• Firewalls
• WS are the best SOAP is designed to work in such
  environments (CORBA IIOP does not have a specific
  port for the communication)
• Legacy systems
• CORBA is the best a lot of legacy systems
  (including EJBs) can easily communicate with
  CORBA components (DCOM components can easily
  communicate to Web Services using MS.NET)

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Web Services or CORBA? (2/3)

• Stateful applications
• CORBA is the best the state is managed by the
  object (WS require more work)
• Mobile users
• WS are the best HTTP support easily IP changing
  and unreliable networks (CORBA wireless is under
  development)
• Thin clients
• WS are the best SOAP is light and XML parsers
  can easily discard non suited tags (CORBA
  requires the entire ORB implemented)
• Transparent proxies
• WS are the best SOAP is easy to interface with
  new components that process or change the content
  of the message (CORBA has proxies for specific
  applications such as load balancing, caching,
  etc.)

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Web Services or CORBA? (3/3)

• Real-time performances
• To experiment at present there are several
  real-time applications in CORBA. Its technology
  is more mature and this is a the crucial factor
  to choose the implementation technology. Its too
  early to compare with WS.

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WS-CORBA interoperation

• An automated conversion between SOAP messages and
  IIOP messages is required
• Management of different paradigms OO,
  message-oriented
• XML Schema IDL mapping
• SOAP-CORBA bridge are available but suffer of
  several limitations

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Java XML
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XML Parsers

• There are three fundamental parser type
• A model parser reads an entire document and
  creates a representation of the document in
  memory
• Model parsers use significantly more memory than
  other types of parsers
• A push parser reads through an entire document.
  As it encounters various parts of the document,
  it notifies a listener object
• This is how the popular SAX API operates
• A pull parser reads a little bit of a document at
  once. The application drives the parser through
  the document by repeatedly requesting the next
  piece

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XML Parsers

• Which type you choose depends on how you want
  your application to behave and what types of
  documents you are expecting to parse

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SAX (Simple API for XML)

• SAX provides an event-based framework for parsing
  XML data
• SAX defines events that can occur during the XML
  parsing process
• Example
• SAX defines an org.xml.sax.ContentHandler
  interface that defines methods such as
  startDocument() and endElement()
• Implementing this interface allows complete
  control over these portions of the XML parsing
  process

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DOM (Document Object Model)

• While SAX only provides access to the data within
  an XML document, DOM is designed to provide a
  means of manipulating that data
• DOM provides a representation of an XML document
  as a tree
• DOM also reads an entire XML document into
  memory, storing all the data in nodes, so the
  entire document is very fast to access
• It is all in memory for the length of its
  existence in the DOM tree

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JAXP (Java API for XML Parsing)

• JAXP provides a vendor neutral-interface to the
  underlying DOM or SAX parser
• It adds some convenient methods to make the XML
  APIs easier to use for Java developers

javax.xml.parsers
DocumentBuilderFactory DocumentBuilder
SAXParserFactory SAXParser
ParserConfiguratonException FactoryConfigurationEr
ror
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SAX Example (1/4)

• import org.xml.sax.
• import org.xml.sax.helpers.
• import java.io.
• import javax.xml.parsers.
• public class SAXDemo extends DefaultHandler
• public static void main(String args)
• if (args.length ! 1)
• System.err.println("Usage cmd filename")
• System.exit(1)
• DefaultHandler handler new SAXDemo()
• SAXParserFactory factory SAXParserFactory.newI
  nstance()

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SAX Example (2/4)

• try
• // Parse the input
• SAXParser saxParser factory.newSAXParser()
  
• saxParser.parse( new File(args0),
  handler)
• catch (Throwable t)
• t.printStackTrace()
• System.exit(0)
• //
  
• // SAX DocumentHandler methods
• //
  
• public void startDocument() throws
  SAXException
• System.out.println("START DOCUMENT")

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SAX Example (3/4)

• public void endDocument() throws SAXException
• System.out.println("END DOCUMENT")
• public void startElement(String namespaceURI,
• String lName, // local name
• String qName, // qualified name
• Attributes attrs)
• throws SAXException
• System.out.println("ELEMENT " qName)
• if (attrs ! null)
• for (int i 0 i lt attrs.getLength() i)
• String aName attrs.getQName(i) // Attr
  name
• System.out.println("ATTR " aName " "
  attrs.getValue(i))

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SAX Example (4/4)

• public void characters(char ch, int start, int
  length) throws SAXException
• String s new String(ch, start, length)
• System.out.println("CHARS " s)
• public void endElement(String namespaceURI,
  String sName, // simple name
• String qName // qualified name)
  
• throws SAXException
• System.out.println("END ELEMENT " qName)

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DOM Example 1 (1/3)

• import java.io.
• import javax.xml.parsers.
• import org.xml.sax.
• import org.w3c.dom.
• public class DOMDemo
• public static void main(String args)
• if (args.length ! 1)
• System.err.println("Usage cmd filename")
• System.exit(1)
• Document doc null
• DocumentBuilder db null
• DocumentBuilderFactory dbf DocumentBuilderFacto
  ry.newInstance()

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DOM Example 1 (2/3)

• try
• db dbf.newDocumentBuilder()
• doc db.parse(new File(args0))
• doc.normalize()
• catch (ParserConfigurationException pce)
• pce.printStackTrace()
• catch (SAXException se)
• se.printStackTrace()
• catch (IOException ioe)
• ioe.printStackTrace()
• NodeList nl doc.getChildNodes()
• queryDocument(nl)

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DOM Example 1 (3/3)

• public static void queryDocument(NodeList nl)
• for (int i0 iltnl.getLength() i)
• Node n nl.item(i)
• if (n instanceof Element)
• Element e (Element) n
• System.out.println(e.getNodeName())
• queryDocument(e.getChildNodes())
• else if (n instanceof Text)
• Text t (Text) n
• System.out.println(t.getNodeValue())

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DOM Example 2 (1/4)

• import java.io.
• import javax.xml.parsers.
• import javax.xml.transform.
• import javax.xml.transform.stream.
• import javax.xml.transform.dom.
• import org.w3c.dom.
• public class DomDemo2
• public static void main(String args)
• Document doc null
• DocumentBuilder db null
• if (args.length ! 1)
• System.err.println("Usage cmd filename")
• System.exit(1)

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DOM Example 2 (2/4)

• DocumentBuilderFactory dbf DocumentBuilderFactor
  y.newInstance()
• try
• db dbf.newDocumentBuilder()
• doc db.newDocument()
• catch (ParserConfigurationException pce)
• System.err.println("Parser configuratione
  exception.")
• createDocument(doc)
• serialize(doc, new File(args0))

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DOM Example 2 (3/4)

• public static void createDocument(Document doc)
• Element root doc.createElement("Agenda")
• doc.appendChild(root)
• Element person doc.createElement("Person")
• Person.setAttribute("id", "1")
• root.appendChild(person)
• Element name doc.createElement("Name")
• name.appendChild(doc.createTextNode("Marco"))
• person.appendChild(name)
• Element surname doc.createElement("Surname")
• surname.appendChild(doc.createTextNode("Scotto"))
  
• person.appendChild(surname)
• Element email doc.createElement("Email")
• email.appendChild(doc.createTextNode("scotto_at_dist
  .unige.it"))
• person.appendChild(email)

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DOM Example 2 (4/4)

• public static void serialize(Document doc, File
  file )
• Transformer serializer null
• StreamResult streamResult null
• DOMSource domSource new DOMSource(doc)
• try
• serializer TransformerFactory.newInstance().
  newTransformer()
• serializer.setOutputProperty(OutputKeys.INDENT
  , "yes")
• streamResult new StreamResult(new
  FileOutputStream(file))
• serializer.transform(domSource,
  streamResult)
• catch (Exception e)
• e.printStackTrace()

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DOM or SAX?

• DOM
• Suitable for small documents
• Easily modify document
• Memory intensive load the complete XML document
• SAX
• Suitable for large documents saves significant
  amounts of memory
• Event driven
• Limited standard functions

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XML Parsers for J2ME

• The following table summarizes the current
  offering of small XML parsers that are
  appropriate for J2ME

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XPath

• Language for addressing and matching parts of an
  XML document
• Designed to be used standalone, but also by
  XPointer, XSLT, XQuery.
• Uses a compact, non-XML format to facilitate use
  within URIs and attribute values
• Provides basic facilities for string, number and
  boolean manipulation
• Supports namespaces

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XPath Example (1/2)

• Sample XML document
• ltAgendagt
• ltPerson NameMarco SurnameScottogt
• ltemailgtscotto_at_dist.unige.itlt/emailgt
• lt/Persongt
• ltPerson NameMario SurnameRossigt
• ltemailgtMario.Rossi_at_email.itlt/emailgt
• lt/Persongt
• lt/Agendagt

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XPath Example (2/2)

• Selects the name attribute of the first person
  element
• /Agenda/Person1/_at_Name
• Selects the surname attribute of the first person
  element
• /Agenda/Person1/_at_Surname
• Selects the email of the first person element
• /Agenda/Person1/email/text()