Session Beans and Business Logic

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Session Beans and Business Logic

• Presented By
• Sethu Ram Kettimuthu

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For Starters.. ?
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A look at the Forest

• What is a middle ware?
• Middleware is a layer of software between the
  network and the applications that provides
  services such as identification, authentication,
  authorization, directories, and security.
• By promoting standardization and
  interoperability, middleware will make advanced
  network applications much easier to use.

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Trees of the Forest

• CORBA

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Corba (Contd)

• The CORBA specification only defines a set of
  conventions and protocols that must be followed
  by CORBA implementations
• CORBA does not make any restrictions on language
  or underlying operating system
• Because of CORBA's heterogeneous nature, a
  neutral language was needed to perform the task
  of defining the interfaces to ORB-based objects
• You can implement IDL interfaces using any
  programming language for which an IDL mapping is
  available

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E-Speak

• Fundamentally e-speak is a distributed
  development environment, just like Java/RMI, just
  like CORBA, just like the Web itself
• To access a service, a client
• Creates a connection to the e-Speak engine 
• Identifies a contract and vocabulary to use when
  searching for services 
• Locates the service using ESServiceFinder 
• Invokes the methods specified by the service
  interface 

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.Net Com

• With .NETMicrosoft's new Web services
  platformyour applications, services, and devices
  work together to provide access to the
  information you need at anytime and any place
• .net is MS equivalent of J2EE
• Com is MS equivalent of EJB
• C is MS equivalent of Java

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Now to EJB..at last

• Why EJB?
• EJB enables rapid development of
  mission-critical application that are versatile,
  reusable and portable across middleware while
  protecting IT investment and preventing vendor
  lock-in
• What is EJB?
• Enterprise beans are server components written
  in the Java programming language.
• Enterprise beans contain the business logic for
  your application.
• For example, a checkbook client might invoke
  the debit and credit methods of an account
  enterprise bean

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key features of the EJB technology

• EJB components are server-side components written
  entirely in the Java programming language
• EJB components contain business logic only
• System-level services are automatically managed
  for the EJB component by the EJB server
• EJB components are fully portable across any EJB
  server and any OS

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Types of enterprise beans

• Session Beans
• (More on Session Beans rest of the seminar)
• Entity Beans
• - An entity bean represents a business object in
  a persistent storage mechanism such as a database
• - May be shared by multiple clients
• - Persistent - even when the EJB container
  terminates, the entity state remains in a
  database.

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Session Beans

• Purpose Performs a task for a client
• Shared Access May have one client
• Persistence Not persistent. When the client
  terminates its session bean is no longer
  available.

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Session Beans Contd..

• The client accesses remote services by invoking
  the session bean's methods.
• The session bean performs work for its client,
  shielding the client from complexity by executing
  business tasks inside the server
• It is similar to an interactive session
• The Session Beans Terminates with the client
• Session beans are powerful because they extend
  the reach of your clients into remote servers--
  yet they're easy to build

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How to Write Session Beans

• To write a session enterprise bean class, the
  class must implement the javax.ejb.SessionBean
• interface
• The javax.ejb.SessionBean interface extends the
  more generic javax.ejb.Enterprise Bean interface
• So does the javax.ejb.EntityBean

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Methods in SessionBean Interface

• Javax.ejb.SessionBean Interface
• Public interface javax.ejb.SessionBean extends
  javax.ejb.EnterpriseBean
• public abstract void setSessionContext(SessionCon
  text ctx)
• throws java.rmi.RemoteException
• public abstract void ejbPassivate() throws
  java.rmi.RemoteException
• public abstract void ejbActivate() throws
  java.rmi.RemoteException
• public abstract void ejbRemove() throws
  java.rmi.RemoteException

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A look at each method

• setSessionContext(SessionContext ctx)
• Container calls this method to associate the bean
  with a session context
• A session context is the beans gateway to
  interact with the container
• The bean can use the session contexts to query
  the container about the current transactional
  state,security state etc..

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A look at each method

• ejbCreate(..)
• Initializes the session bean
• Can define one or more ejbCreate() methods and
  each can take different arguments
• Can perform any initialization the bean
  needs,ie.,
• public class MyBean implements SessionBean
• private int memberVar
• public void ejbCreate(int init val)
• this.memberVar initval
• .

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A look at each method

• ejbPassivate()
• If too many beans are instantiated, the EJB
  container can passivate some of them(by writing
  the beans to a temp storage like a DB or File)
• The container can then release the Resources the
  beans had claimed
• Immediately before the Beans are passivated the
  container calls the ejbPassivate() method
• NOTE Remember that passivation doesnt apply to
  stateless bean as it cannot hold the state.

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A look at each method

• ejbActivate()
• When a client needs to use the passivated bean
  then the container kicks the bean back into
  memory. This is activation.
• Once the bean is back in the memory again , the
  beans implementation acquires any resource the
  bean needs.
• NOTE Activation doesnt apply to stateless
  session beans as it cannot hold state and can
  simply be created/destroyed rather than
  passivated/activated

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Guess who spoke this ?

• "You've heard Al Gore say he invented the
  internet. Well, if he was so smart, why do all
  the addresses begin with "W"?
• Any body ?

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A look at each method

• ejbRemove()
• When the container is about to remove your
  session bean instance it calls the beans
  ejbRemove() method
• ejbRemove is a clean-up method, alerting the bean
  that it is about to destroyed.
• ejbRemove() is a required method of all beans and
  takes no parametrs.
• There is only one ejbRemove() method per bean.

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A look at each method

• Business Methods
• There can be zero or more Business methods in
  your bean
• These methods actually solve business problems
• For eg
• public class MyBean implements SessionBean
• public int add(int I,int j)
• return(I j)
• For clients to call your business methods, the
  business methods must be listed in the beans
  remote interface

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Major parts of an EJB Application

• Session Bean Class
• Home Interface
• Remote Interface
• Deployment Descriptor

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Two types of State

• Transactional state
• Roughly speaking this is the data stored in the
  persistent store
• Multiple client can read and modify the data
  without conflict
• If the App Server crashes or re-started the data
  is still available in the data store
• Example An order that a customer has placed

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Two types of State

• Conversational State
• Cached data either on the Client or Server
• Private data that isnt accessible to other
  clients
• Example The web shopping cart before the order
  has been confirmed
• REMEMBER A stateless session bean holds
  conversations that span a single method call.
• So it doesnt hold Conversational state, BUT
• stateful session bean holds Conversational state

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Types of Session Beans

• Stateless Session Beans
• Stateful Session Beans
• (Well see about this later)

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Stateless Session Beans(SLSB)

• A stateless session bean does not maintain a
  conversational state for a particular client
• When a client invokes the method of a stateless
  bean, the bean's instance variables may contain a
  state, but only for the duration of the
  invocation
• The state is not customized for each client
• The SLSB cannot retain state between method
  calls,but they also cannot retain state after a
  client passes data to an ejbCreate() call
• So all SLSB may expose only a single ejbCreate()
• method,which takes no parameters

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Stateless Session Bean Pooling

• Stateless session bean pool

Client
Invoke()
Remote Interface
bean
EJB Obj
bean
bean
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Hello world SLSB

• Function
• The SLSB, a component running in a Distributed
  Environment will do the mighty task of returning
  the string Hello World to the client.

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Hello world Remote Interface

• The remote interface is what the clients operate
  on when they interact with EJB objects. The
  container vendor will implement this interface
  the implemented object is the EJB object,which
  delegates invocations to the actual bean
• import javax.ejb.
• import java.rmi.RemoteException
• Import java.rmi.remote
• Public interface Hello extends EJBObject
• public String hello() throws
  java.rmi.RemoteException

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Implementing the Hello world bean

• / Stateless Session bean /
• import javax.ejb.
• public class HelloBean implements SessionBean
• / EJB required methods /
• public void ejbCreate( ) System.out.println(C
  reate Method)
• public void ejbremove( ) System.out.println(
  Remove Method)
• public void setSessionContext(SessionContext
  ctx)
• System.out.println(Set Session Context)
• // Business Methods
• public String hello() System.out.println(Hell
  o())
• return Hello World

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Hello World Home Interface

• The Home Interface for HelloBean is implemented
  by the EJB Servers glue-code tools- the
  implemented object is called the Home Object and
  serves as the factory for EJB Objects
• import javax.ejb.
• import java.rmi.RemoteException
• / One create() method is in this Home INTERFACE
  /
• public interface HelloHome extends EJBHome
• / This method creates the EJB Object return
  the newly created EJB object/
• Hello create() throws RemoteException,
  CreateException

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Deployment Descriptor
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EJB-JAR File

• Last step before deploying
• Package all the files above in an EJB-Jar file
• Jar files are compact modules in which to wrap
  our beans
• The files to be included are
• Enterprise Bean
• Remote Interface
• Home interface
• Deployment Descriptor

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Client pseudo-code for Stateless Bean

• The HelloClient class invokes methods on a simple
  stateless beans
• Get system properties for JNDI initialization
• Form an initial context
• Get a reference for the home object(factory for
  EJB Objects)
• Use the factory to create EJB Object
• Call the Hello() method and print the string
• Since the EJB object is done with, remove it /
  hello.remove /
• Check for any Exception

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Lifecycle of a SLSB
Because a stateless session bean is never
passivated, its life cycle has just two stages
non-existent and ready for the invocation of
business methods.
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Stateful Session Beans

• Stateful Session Beans are conversational beans
• Because they hold conversation with clients that
  span multiple method invocations
• Stateful Session Bean store conversatinal state
  within the bean
• The conversational state is specific to a
  particular client

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Passivation of Stateful bean
Client
Remote Interface
bean
EJB Obj
bean
bean
Passivated Bean stored
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Stateful Session bean Lifecycle
Does not exist
1.create
1.remove
2. setSessionContext
2. ejbRemobe
3 ejbCreate
ejbPassivate
Ready
Passive
ejbActivate
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CartEJB.java
import java.util.
import javax.ejb.
 
public class CartEJB implements SessionBean
 
String customerName
String customerId
Vector contents
 
public void ejbCreate(String person) throws
CreateException
 
if (person null)
throw new CreateException("Null person
not allowed.")

else
customerName person

 
customerId "0"
contents new Vector()

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public void ejbCreate(String person, String id)
throws CreateException
 
if (person null)
throw new CreateException("Null person
not allowed.")

else
customerName person

 
IdVerifier idChecker new IdVerifier()
if (idChecker.validate(id))
customerId id

else
throw new CreateException("Invalid id "
id)

 
contents new Vector()

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public void addBook(String title)
 
contents.addElement(title)

public void removeBook(String title) throws
BookException
 
boolean result contents.removeElement(titl
e)
if (result false)
throw new BookException(title " not in
cart.")


public Vector getContents()
return contents

public CartEJB()
public void ejbRemove()
public void ejbActivate()
public void ejbPassivate()
public void setSessionContext(SessionContext
sc)
 

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The SessionBean Interface The SessionBean
interface extends the EnterpriseBean interface,
which in turn extends the Serializable
interface. The SessionBean interface declares
the ejbRemove, ejbActivate, ejbPassivate, and
setSessionContext methods
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The ejbCreate Methods Because an enterprise
bean runs inside an EJB container, a client
cannot directly instantiate the bean. Only the
EJB container can instantiate an enterprise
bean. During instantiation, the example program
performs these steps 1. The client invokes a
create method on the home object
Cart shoppingCart home.create(Sethu","123")
2. The EJB container instantiates the enterprise
bean. 3. The EJB container invokes the
appropriate ejbCreate method in CartEJB
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public void ejbCreate(String person, String id)
throws CreateException
 
if (person null)
throw new CreateException("Null person
not allowed.")

else
customerName person

 
IdVerifier idChecker new IdVerifier()
if (idChecker.validate(id))
customerId id

else
throw new CreateException("Invalid id "
id)

 
contents new Vector()

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Business Methods The primary purpose of a session
bean is to run business tasks for the client. The
client invokes business methods on the remote
object reference that is returned by the create
method. From the client's perspective, the
business methods appear to run locally, but they
actually run remotely in the session bean. The
following code snippet shows how the CartClient
program invokes the business methods
Cart shoppingCart home.create("Duke DeEarl",
"123")
. . .
shoppingCart.addBook("The Martian Chronicles")
shoppingCart.removeBook("Alice In Wonderland")
bookList shoppingCart.getContents()
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The CartEJB class implements the business methods
in the following code
public void addBook(String title)
contents.addElement(new String(title))

public void removeBook(String title) throws
BookException
boolean result contents.removeElement(title)
if (result false)
throw new BookException(title " not in
cart.")


public Vector getContents()
return contents  
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Home Interface A home interface extends the
EJBHome interface. The purpose of the home
interface is to define the create methods that a
client may invoke. The CartClient program, for
example, invokes this create method
Cart shoppingCart home.create("Duke DeEarl",
"123") Every create method in the home
interface corresponds to an ejbCreate method in
the bean class. The signatures of the ejbCreate
methods in the CartEJB class follow
public void ejbCreate(String person) throws
CreateException
. . .
public void ejbCreate(String person, String id)
throws CreateException
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create methods in the CartHome interface
import java.io.Serializable
import java.rmi.RemoteException
import javax.ejb.CreateException
import javax.ejb.EJBHome
 
public interface CartHome extends EJBHome
Cart create(String person) throws
RemoteException,

CreateException
Cart create(String person, String id) throws
RemoteException,

CreateException

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Remote Interface The remote interface, which
extends javax.ejb.EJBObject, defines the business
methods that a client may invoke. Here is the
source code for the Cart remote interface
import java.util.
import javax.ejb.EJBObject
import java.rmi.RemoteException
 
public interface Cart extends EJBObject

public void addBook(String title) throws
RemoteException
public void removeBook(String title) throws
BookException,

RemoteException
public Vector getContents() throws
RemoteException

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You should consider using a stateful session bean
if any of the following conditions are true

• The bean's state must be initialized when it is
  created.

• The bean needs to hold information about the
  client across method invocations.

• The client is an interactive application.
• Since the primary goal of a session bean is to
  represent a client in the J2EE server, most of
  your session beans will be stateful. However,
  sometimes you may want to use stateless session
  beans

• The bean performs a task that is not tailored to
  the needs of a particular client. For example,
  you might use a stateless session bean to fetch
  from a database a commonly used set of data.
• The bean doesn't need to hold information about
  the client across method invocation

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FIRE .
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Am Still Alive !!!!
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References

• On Starters
• www.calvinandhobbes.com
• More on HIS Quotes
• www.bushisms.com
• More on EJB
• ????????????
• Ask Google or Dr. juggy ?
• Actually gt 1) Text Mastering EJB by Ed roman
• 2) www.javaworld.com
• 3) http//java.sun.com/products/e
  jb/
• 4) http//theserverside.com/home/index.j
  sp