Overview of The Java Platform Solution for E-Business Applications : JSP, Servlet and EJB

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Overview of The Java Platform Solution for
E-Business Applications JSP, Servlet and EJB
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Outline

• Big picture
• Servlets
• JavaServer Pages
• EJB

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Multi-Tiered Web-based application
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What are Servlets?

• Extend HTTP Server
• Dynamic content
• Servlets are lightweight
• Run in web server process
• exploit Java security
• Built on Java Platform
• Full access to Java APIs
• Easy to develop. Write once, run anywhere

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HTTP Requests Response

• Client makes HTTP request
• Request is resolved to Servlet
• Container
• creates servlet
• invokes init()
• creates request and response objects
• invokes service()
• Sevlet interact with response
• Container replies to HTTP request
• Container may
• invoke destroy(), dispose servlet at anytime

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A servlet example

• public class HelloServlet extends HttpServlet
• public void doGet(HttpServletRequest request,
• HttpServletResponse response)
• response.setContentType("text/plain")
• PrintWriter out response.getWriter()
• out.println("lthtmlgt")
• out.println("Hello World!")
• out.println("ltbrgt")
• JspCalendar clock new JspCalender()
• out.println("Today is")
• out.println("ltulgt")
• out.println("ltligtDay of month ")
• out.println(clock.getDayofMonth())
• out.println("ltligtYear ")
• out.println(clock.getYear())
• out.println("/ltulgt")
• out.println("lt/htmlgt")

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As a JSP page

• lthtmlgt
• Hello World!
• ltbrgt
• ltjspuseBean id"clock"
• class"calendar.JspCalendar"gt
• Today is
• ltulgt
• ltligtDay of monthltclock.getDayofMonth()gt
• ltligtYear ltclock.getYear()gt
• lt/ulgt
• lt/htmlgt

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JavaServer Pages (JSP)

• JSP builds on servlet semantics
• inside-out servlets (JSP can be precompiled
  into Servlet to reduce start up time)
• Benefits
• Easier to author, separate presentation logic
  from business logic
• Exploits
• server-side scripting
• templates
• encapsulation of functionality

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Distributed Java Component Model -
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The Problem

• Developing enterprise applications is
• HARD
• Developing enterprise applications is
• EXPENSIVE
• Enterprise applications are a
• NIGHTMARE TO MAINTAIN
• Enterprise applications are
• COMPLEX TO ADMINISTER

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Why is it HARD?

• Difficult to reuse application code across
• hardware platforms
• software platforms
• servers
• databases
• Service needs grow more complex
• threading
• persistence
• transactions

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What is EJB?

• Its server component model
• Its part of Java platform for the enterprise
• Its a specification (for software
  interoperability)
• It enables development and deployment of Java
  applications that are
• Distributed via RMI
• Scalable
• Transactional
• Secure

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Distributed component models -we are in heaven
...
IIOP
IIOP
IIOP
CORBAServerService
RMIServerService
RMIClient
JRMP
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The underlying mechanism...
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Advantages of server side component model

• Using pre-developed pieces of application
• Transparent access to the distributed services,
  i.e. hiding the complexity of the technical
  environment
• Components can be shared across the Enterprise
• Using tools to wire components together

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EJB Architecture
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EJB Architecture
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EJB Main Components

• Client
• Any application or service requesting a service
• Can be written in any language
• Cant access EJBs directly must go through RMI
  and container
• Name lookup via JNDI
• EJB Servers
• Contains and runs 1 or more containers
• Resource management
• process, thread, and connection pools
• Remote management API

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EJB Main Components

• EJB Containers
• Actually host the beans
• Provide naming (via JNDI), life cycle,
  persistence, security, transactions through call
  interception
• EJB Components
• Are distributed, transactional, and secure
• Simple, single threaded, and non-re-entrant
• Developer or tool generated
• Contain business logic

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Roles in developing EJB

• Enterprise Bean provider
• Application Assembler
• Deployer
• EJB Server Provider
• System Administrator

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Varieties of EJBs

• Session beans
• Model application tasks
• Not shared, client specific
• Transient state
• Short lived
• Example an object holds the logic for
  purchasing product items i.e. buyProduct

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Varieties of EJBs

• Entity bean
• Model persistent resources
• Shared by clients
• Persistent state
• Long lived
• Example a product to be purchased in a shop

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Programming basics Classes and Interfaces

• Remote interface
• Defines the beans business methods
• Extends javax.ejb.EJBObject
• Home interface
• Defines the beans life cycle methods (creating,
  removing and finding a bean)
• Extends javax.ejb.EJBHome

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Programming basics Classes and Interfaces

• Bean class
• Must have methods matching the signatures of the
  methods defined in the remote interface
• Must have methods corresponding to some of the
  methods in the home interface
• Primary key
• Provides a pointer into the database
• Only entity beans need a primary key

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The Unseen Pieces
Client
EJB Server
EJB home stub
home interface
home interface
EJB home
EJB Object
remote interface
bean class
remote interface
EJB object stub
RMI allows the downloadable stub
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Big picture again
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Several good introduction material on the web

• http//java.sun.com/products/ejb/articles/multitie
  r.html
• This article shows a very good example on how to
  use EJB to develop multi-tier application!!! The
  example pretty much covers every thing (Session
  Bean, EntityBean and Servlet).
• http//java.sun.com/products/ejb/faq.html
• The FAQs on Sun EJB web site answered many
  general questions regarding to EJB.
• http//internt.isk.kth.se/enander/DistObj/ejb/ejb
  pre.htm
• here's a good EJB presentation

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The EJB Object

• Therere a number of strategies that a vendor can
  use to implement the EJB object

java.ejb.EJBObject
Cabin
javax.ejb.EntityBean
Cabin_EJB_Object
CabinBean
a
b
Java interface
Java class
extends
implements
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Example

• Remote interface
• public interface Cabin extends javax.ejb.EJBObject
  
• public void setDeckLevel(int level) throws
  RemoteException
• public int getDeckLevel() throws
  RemoteException
• Home Interface
• public interface CabinHome extends
  javax.ejb.EJBHome
• public Cabin create(int id) throws
  CreateException,RemoteException
• public Cabin findByPrimaryKey(CabinPK pk) throws
  FinderException,RemoteException

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Example bean class

• public class CabinBean implements
  javax.ejb.EntityBean
• public int id
• public int deckLevel
• public void ejbCreate(int id)this.id id
• public void ejbPostCreate (int id)
• public int getDeckLevel()return deckLevel
• public void setDeckLevel(int level)deckLevel
  level
• public void setEntityContext(EntityContext ctx
• public void unsetEntityContext()
• public void ejbActivate()
• public void ejbPassivate()
• public void ejbLoad()
• public void ejbStore()
• public void ejbRemove()