Client/Server Distributed Systems

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Client/Server Distributed Systems
240-322 Semester 1, 2005-2006
14. J2EE and Web Services

• Objectives
• introduce the J2EE specification, and the J2EE
  SDK
• other approaches Struts, Spring
• Web Services (XML-RPC)

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Contents

• 1. What is J2EE?
• 2. J2EE Overview
• 3. Some Services Explained
• 4. Using Sun's J2EE SDK
• 5. More Information on J2EE
• 6. Struts
• 7. Spring
• 8. Web Services

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1. What is J2EE?

• J2EE is the Java 2 Enterprise Edition
• J2EE helps with the construction of Web-based
  client/server applications
• it supports simplified networking, concurrency,
  transactions, easy access to databases, etc.

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• J2EE emphasies n-tier client/server design.
• Application development uses objects, beans, and
  components.
• J2EE is not language neutral
• tightly connected to Java

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• Sun initially released J2EE as a specification,
  which has been implemented by different vendors
• e.g Tomcat from the Jakarta Project
• http//jakarta.apache.org/tomcat/
• e.g. JRun from Macromedia (Allaire)
• http//www.macromedia.com/software/jrun
• The Sun implementation
• http//java.sun.com/j2ee/

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2. J2EE Overview
JDBC
presentation logic
JavaMail
JSPs
Tag libraries
applet/ appl.
servlets
RMI
app.
deploymentdescription
client
Web container
IIOP
CORBA
EJB container
business logic
JNDI
Entity beans
Session beans
JMS
server-side application
network
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• A server-side application usually has two parts
• presentation logic in the Web container
• to create HTML pages (and other formats)
• business logic in the EJB container
• to handle server-side processing

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3. Some Service Explained

• Servlets
• a servlet is a Java object on the server side
  that can repond to an HTTP message (GET, POST,
  etc) by calling a method
• the results of the method is sent back to the
  client as a Web page

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• JSP (Java Server Pages)
• JSPs dynamically generate Web pages by using
  servlets
• EJB (Enterprise Java Beans)
• Java objects with predefined methods for
  simplifying network and inter-object communication

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• Java IDL (Interface Definition Lang.)
• a language which allows Java objects to interact
  with CORBA objects
• RMI-IIOP
• a bridge between Javas RMI and the communication
  protocol used by CORBA over the Internet (IIOP)

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• JTA (Java Transaction API)
• JTA lets a Java object control transactions
  (e.g. bank account updates)
• JMS (Java Message Service)
• JMS lets a Java object asynchronously send
  messages to other objects

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• JNDI (Java Naming Directory Interface)
• JNDI lets a Java object find other objects (over
  the network) by using their names

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• The deployment description is a text file
  containing various information on how to
  configure/initialise the server-side application
• the information is written in XML format

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4. Using Sun's J2EE SDK

• J2EE SDK is Sun's implementation of the J2EE
  specification.
• The latest version
• Java 2 SDK, Enterprise Edition,
  v.1.4http//java.sun.com/j2ee/1.4/
  download.html
• also obtain the tutorial for v.1.4 from the page

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• This release is available for the following
  platforms
• Solaris, Windows 2000 Prof. Ed., Windows XP
  Prof. Ed., Linux Redhat
• The API documentation is packaged with the
  download bundle.

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• To download J2EE SDK v.1.4, you have to register
  as a member of the Java Developer Connection
• membership is free
• Easier to get it from Aj. Somchai's site
• http//java.coe.psu.ac.th/ RefImp.htmlJ2EE
• 102 Mb for everything

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Sun's J2EE SDK as a Diagram
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Java Server Faces (JSF)

• An API for building Web-based client-side user
  interfaces from components.
• communication to the server side is built-in
• the components are extensible
• Simplifies the design and implementation of the
  presentation level of client/server applications.

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• Coding is based on listening for events.
• JSF 1.2 will be integrated into the next release
  of J2EE (version 1.5, renamed to 5.0)

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JSTL

• The JavaServer Pages Standard Tag Library
• structural tasks, such as iteration and
  conditionals
• tags for manipulating XML documents
• internationalization tags
• SQL tags
• a framework for integrating existing custom tags
  with JSTL

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Ant

• The compilation of the examples in the J2EE
  tutorial use Ant, a Java-based make utility,
  found at
• http//jakarta.apache.org/ant/
• Ant v.1.6.2 (and before) are available here
• http//java.coe.psu.ac.th/ OpenSource.htmlAnt

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5. More Information on J2EE

• J2EE main site
• http//java.sun.com/j2ee/
• it has links to pages dedicated to parts of J2EE
  (e.g. EJB, JSP, servlets, XML)
• Aj. Somchai's J2EE books section
• http//java.coe.psu.ac.th/
  ForMember/Books.htmlJ2EE

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6. Struts
notifies
controller
model
view
updates

• An open source framework
• intended to be a simpler replacement for J2EE
• many components of J2EE can be used
• http//struts.apache.org/
• Utilises the Model-View-Controller (MVC) design
  style for applications.

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• Model tools
• JDBC, EJB, Hibernate
• View tools
• JSP, XML/XSLT, JSF
• Controller tools
• servlets, tag libraries, specific to Struts
• Available from
• http//struts.apache.org/

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7. Spring

• Another open source framework
• intended to be a simpler replacement for J2EE
• many components of J2EE can be used
• http//www.springframework.org/
• Utilises the Inversion of Control (IoC)design
  pattern
• the framework does more (manages more) , the
  programmer codes less

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• The core of Spring's design is the
  org.springframework.beans package, designed for
  working with Java Beans
• objects utilise standard get/set methods to
  simplify communication
• A Spring bean factory enables objects to be
  retrieved by name, and manages relationships
  between objects.

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• Configuration details are specified using XML and
  method prototypes.
• Unit testing is simpler.
• Primary use is to replace or simplify EJB
  applications.

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8. Web Services

• A collection of XML-based APIs for allowing
  Web-based (J2EE) applications to
• exchanging messages
• describing their services/capabilities
• publish their Web service description(s)
• find other Web service descriptions

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8.1. Web Service Architecture
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8.2. Some Web Services APIs

• Simple Object Access Protocol (SOAP)
• XML-based messaging protocol
• Web Services Description Language (WSDL)
• XML language for describing Web services and
  their capabilities
• Java API for XML Registries (JAXR)
• language for building XML directories of
  information about Web services

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• Java API for XML-based RPC (JAX-RPC)
• language for converting remote procedure call
  data into XML
• Java API for XML Messaging (JAXM)

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8.3. Focus on XML-RPC

• An implementation of RPC which uses HTTP and XML
  to support remote method calls
• there are implementations for Java, C, PHP,
  etc.
• http//www.xmlrpc.com

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• The most popular Java implementation of XML-RPC
  is Apache XML-RPC
• http//xml.apache.org/xmlrpc
• part of the larger Apache XML project

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XML-RPC Approach
1. send inputs as XML in a POST message
XML-RPCserver
int x sqS.square(14)
2. send result as aHTTP response page
XML-RPC client
sqS handler
at foobar.com
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Example XML-RPC Request

• POST /XMLRPC HTTP/1.0Host foobar.comConnection
  CloseContent-Type text/xmlContent-Length
  151User-Agent OSE/XML-RPClt?xml
  version"1.0"?gtltmethodCallgt ltmethodNamegtsqS.squ
  arelt/methodNamegt ltparamsgt ltparamgt
  ltvaluegt ltintgt14lt/intgt lt/valuegt
  lt/paramgt lt/paramsgtlt/methodCallgt

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XML-RPC Response

• HTTP/1.0 200 OKDate Wed, 11 May 2005 220809
  GMTServer Apache/1.3.26 (Unix)Content-Length
  157Connection closeContent-Type
  text/xmllt?xml version"1.0"?gtltmethodResponsegt
  ltparamsgt ltparamgt ltvaluegt
  ltintgt196lt/intgt lt/valuegt lt/paramgt
  lt/paramsgtlt/methodResponsegt

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Sample Client Code

• // create client link to serverXmlRpcClient
  client new XmlRpcClient(
  "http//foobar.com/XMLRPC")// create a
  parameters vector for the requestVector params
  new Vector()params.addElement( new Integer(14)
  )// send the request and get the
  responseObject resultObj client.execute(
  "sqS.square", params)int result
  ((Integer) resultObj).intValue() //
  result will be 196

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Sample Server Code

• public class SquareServer public
  SquareServer() public Integer square(int x)
  return new Integer( xx )
  

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• public static void main(String args)
  try // invoke XML-RPC server
  WebServer server new WebServer() // add
  handler for the service server.addHandler("s
  qS", new SquareServer())
  catch (Exception ex) // end of
  SquareServer class

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8.4. Web Services Resources

• The Java Web Services Developer Pack (Java WSDP),
  version 1.5
• http//java.sun.com/webservices/
• or
• http//java.coe.psu.ac.th/ RefImp.htmlWebServi
  ces

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• In the CoE library
• Java Web Services for Experienced
  ProgrammersDeitel et al, Prentice Hall, 2003
• very detailed, but a little bit out of date