Slide 1 EE557: Server-Side Development eXtensible Stylesheet Language (XSL) XSL is the language that describes how XML documents are displayed XSL developed.

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EE557: Server-Side Development

eXtensible Stylesheet Language (XSL)• XSL is the language that describes how XML documents are displayed

• XSL developed by the W3C Working Group

• Consists of three parts - XSLT (XSL Transformations)

- XSL Formatting Objects (XSL-FO)- XPath

• XSLT – is the language that specifies the conversion of a document from one format to another, where the XSL stylesheet defines the means -> typically used for for textual transformations, such as HTML or WML from XML

• XSL-FO – formatting objects used when converting XML into binary formats such as PDF files, or Word Documents. This part is not covered by JAXP or here

• XPath – allows you to specify the part of the structure you are talking about It allows you to distinguish between <name><title> and <qualification><title> -> We can describe different transformations for different <title> elements

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<?xml version='1.0'?> <?xml:stylesheet type='text/xsl' href='xslexample1.xsl'?> <personnel>

<person><firstname>David</firstname><lastname>Molloy</lastname>

</person> <person>

<firstname>John Peter</firstname> <lastname>Smith</lastname>

</person> <person>

<firstname>Jane</firstname> <lastname>Grogan</lastname>

</person> </personnel>

xslexample1.xml

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xslexample1.xsl

<?xml version='1.0'?> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0"> stylesheet is the top level element -> root of the XSL stylesheet tree <xsl:template match="/"> associates the template with the root of the doc<HTML> <BODY bgcolor="wheat"> <xsl:for-each select="personnel/person"> works like a ‘for’ loop selects the value of the <person> tag within the <personnel> root element

<BR/><H2>Employee</H2> <B>Firstname: </B><xsl:value-of select="firstname" /><BR/> <B>Lastname: </B><xsl:value-of select="lastname" /><BR/><BR/>

</xsl:for-each> </BODY> </HTML> </xsl:template> </xsl:stylesheet>

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Client-Side/Server-Side Transformations

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Client-Side/Server-Side

• Internet Explorer 5.0+ goes a long way towards implementing client side transformations of XML

• Non standards compliant in many ways with some omissions/changes

• Perform a client transformation example

• Many advantages in performing a manual transformation on the server - works across multiple browsers (HTML) - lightweight clients - transformations are performed in advance – quicker

java –classpath .;xalan.jar org.apache.xalan.xslt.Process –IN xslexample1.xml –XSL xslexample1.xsl -OUT xslexample1.html

• Work through second example in the notes xslcustomers.xml/.xsl

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XSLT and JAXP• Often need to perform transformation real-time with dynamic data • Eg. XML to browser-specific HTML XML to Wireless Markup Language (WML) for mobile phones Personalized webpages/documentation

• JAXP contains four packages responsible for handling XSLT - javax.xml.transform

- javax.xml.transform.dom- javax.xml.transform.sax- javax.xml.transform.stream

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XSLT and JAXP• Steps:

1) Import javax.xml.transform package classes and other classes such as DOM packages if you use DOM

2) Instantiate a TransformerFactory objectTransformerFactory tFactory = TransformerFactory.newInstance()

3) Create a Transformer, in which we can define a set of transformation instructions. In our example, we supply an XSL StreamSource

4) Perform the transformation on the input (which can be created from a SAX reader, a DOM or an input stream) – in our example, we provide a DOMSource. The transform method takes a second argument, which in our example is a File (via a FileWriter)

5) Handle the possible exceptions

• Work through the example in the notes

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Messaging with Java

• Most common form of message is eMail

• This is person-to-person or server-to-person messaging, not application to application messaging

• Email is made up of a Header and Content

• Each header attribute has its own line, with attributes split by a ‘:’

Eg.Precedence: bulkFrom: “David Molloy” [email protected]

• Show full email message from the notes


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Messaging with Java

• Email messages are stored or sent using one of a number of different protocols

- Simple Mail Transfer Protocol (SMTP)- Post Office Protocol (POP3)- Internet Message Access Protocol (IMAP4)

• IMAP4 typically considered more advanced than POP3, since it supports folders and status flags (among other features)


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JavaMail API

• J2EE developer does not need to understand underlying protocols

• JavaMail API includes providers for the most commonly used protocols

• JavaMail sits on top of the electronic mail vendor’s systems

• Provides a standard, independent framework for Java client applications to use electronic mail

• Can use JavaMail to: - Compose messages (including multi-part messages with attachments) - Send messages to particular servers - Retrieve and store messages in folders

• When using JavaMail, the application needs network access to a mail service that can send messages to the destination (dialup or network service)


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JavaMail API• JavaMail is contructed with an Open Architecture, so can support future protocols and standards

• Two different types of protocols providers can implement:

- Transport: is the service which sends messages to the destination Most commonly used transport is SMTP

- Store: the service that provides access to messages that have been delivered to a mailboc. Most commonly used is POP3 but IMAP4 is considered better and becoming more common

• JavaMail relies heavily on the Java Activation Framework (JAF). JAF designed to work in a standard way with different types of data

• When an application needs to work with a particular data type, these JAF objects can be “activated” and used to process data (mail.jar, activation.jar, J2EE standard inclusion)


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JavaMail API

• javax.mail.Session class is starting point for JavaMail. Allows the specification of properties, such as the transport mechanism and the mail server

• Using the Session we can create a new MimeMessageObject

• We then set the properties for the email message, such as the sender, recipient, subject and contents of the message

• Finally, we use Transport.send(message) to open up a new connection to the mail service and send the message

• Show the example code -> issues with running application (local access only etc.) - demoMail.java


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Java Message Service (JMS)• JavaMail is an API for Messaging using email

• Java Message Service (JMS) is an API for Messaging between applications

• Developed by Sun Microsystems as part of the Java 2 Enterprise Ed.

• Provides a common way for Java programmers to create, send, receive and read an enterprise messaging system’s messages

• “A message is a unit of data that is sent from a process running on one computer to other processes running on the same computer or a different computer”

• Messages can be simple text, or more complicated structures such as Java Hashtables or other serializable Java objects

• Object is serializable if it can be transmitted across a network as a series of bytes and re-created into a copy of the original object


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• MOM is a specialized type of middleware that coordinates the sending and receiving of messages

• Provides dependable mechanisms that enable applications to create, send, and receive messages asynchronously in an enterprise environ.

• Numerous examples of MOM:

- IBM MQ Series- Fiorano Message Server- Progress SonicMQ- SilverStream JbrokerMQ

-> JMS provides a standard interface to these MOM products Frees developers from having to write low level infrastructure code, also known as “plumbing”, allowing them to build solutions quicker

• JMS is used and integrates with other components of J2EE (eg. JDBC used for persisting messages, JMS used in MDBs)


Java Message Service (JMS)

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• Two primary communication modes:



1. Synchronous Communication: conducted between two parties, both parties must be active and must acknowledge receipt of a message (known as a blocking call) before proceeding

- easily affected by hardware, software and network failures, resulting in delayed messages and traffic backups

- if hardware capacities are exceeded information is typically lost- Example: chat application

2. Asynchronous Communication: all parties are peers and can send messages at will. Does not require real-time acknowledgement of

messages. Requester can continue with other processing once it sends the message (known as a non-blocking call)

- Example: Email. Even though your e-mail client may not be running on your PC, people can still send multiple messages to you.

- Example: internet-based purchase ring tone system -> return feedback to browser, mobile phone turned off/no signal?

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• Using messaging for exchanging data provides for:



- Easy integration of incompatible systems

- Asynchronous communications

- One-to-many communications

- Guaranteed messaging

- Transactional messaging (all or none, commit/abort)

• JMS supports two message models known as Point-to-Point (PTP) and Publish/Subscribe (Pub/Sub)

• Both models can deliver messages synchronously or asynchronously

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• Sends messages to a receiver on a one-to-one basis, such as in instant messaging, or sending an order to another system

• Message delivered to a queue -> processed on FIFO basis

• Only one receiver can process each message (regardless of number of receivers)

• Receiver can look through messages in a Queue (eg. To count them) but must process them FIFO


Point-to-Point Model (PTP)

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Publish/Subscribe Model

• Applications can publish messages on a one-to-many or many-to-many basis. Eg. Sending news stories to interested parties, stock prices to traders

• Messages are published to a Topic -> one or more publishers can publish messages to a Topic -> clients must subscribe to receive messages -> typically must be subscribed in advance If no clients subscribed, messages are typically destroyed


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JMS API Programming Model

• Firstly, we set up a QueueConnectionFactory or a TopicConnectionFactory for use in our JMS applications

• We achieve this by using the Sun Application Server Admin Console (or whatever console is appropriate for the application server we are using).

• The steps to add the ConnectionFactory are detailed in the notes

At beginning of JMS application, we perform a JNDI API lookup of the connection factory. Eg.

Context ctx = new InitialContext();QueueConnectionFactory queueConnectionFactory = (QueueConnectionFactory) ctx.lookup(“myQueueConnectionFactory”);


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• We also need to define a ‘destination’, which will be either a Queue or a Topic. It defines the target of messages it produces and the source of messages it consumes

• Again we create this resource using the Admin Console

• In our Java application we perform a JNDI lookup for our destination:

Queue myQueue = (Queue) ctx.lookup(“MyQueue”);Topic myTopic = (Topic) ctx.lookup(“MyTopic”);

• Obtain a QueueConnection/TopicConnection to the provider by using the QueueConnectionFactory or TopicConnectionFactory

• Obtain a QueueSession/TopicSession with the provider by using the QueueConnection/TopicConnection



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• Create a QueueSender or QueueReceiver (TopicPublisher or TopicSubscriber) via the QueueSession (TopicSession) for the required Queue (Topic)

• Send and/or receive messages (Publish and/or subscribe messages)

• Close the QueueConnection (automatically closes QueueSender/Receiver, and the QueueSession). For Pub/Sub, close the TopicConnection, TopicPublisher/Subscriber and TopicSession

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JMS Messages• Typically formatted data (such as a request, event or status) passed between applications.

• Message can contain simple or complex data types, including Serializable Java objects

• JMS message is made up of 1 required component and 2 optional: - A header (required) – used for identifying and routing messages,

setting expiration,priority etc. – many settable by clients - Properties (optional) – extra header information- A body (optional) – one of 5 different formats ByteMessage,ObjectMessage,TextMessage,StreamMessage and MapMessage (hashtable type)

message = queueSession.createTextMessage(); for (int i = 0; i < NUM_MSGS; i++) {

message.setText("This is message " + (i + 1)); System.out.println("Sending message: " + message.getText());

}


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Point-to-Point Example

• SimpleQueueSender.java• SimpleQueueReceiver.java


Publish/Subscribe Example

• SimpleTopicPublisher.java• SimpleTopicSubscriber.java• TextListener.java