1. Enterprise Java Beans - (EJB)
By Bharath Reddy Allam
By Bharath Reddy Allam

2. EJB Overview
Enterprise Java Beans Technology is part of larger Framework - The J2EE (Java 2 Enterprise Edition)
Component Architecture for Distributed Systems
Framework for creating middleware

3. Why EJB?
EJB Architecture simplifies the development of distributed enterprise applications.
EJB Specification is a solution that is operating-system independent.
Middleware Independence
EJB defines a solution that eases the development and deployment of distributed applications

4. Why EJB?
EJB enables the development of reusable and portable components.
EJB has Broad Industry Support: Server Vendors and End Users.

5. EJB Vs JavaBeans
EJB component model logically extends the JavaBeans component model to support server components.
EJB components cannot be manipulated by a visual Java IDE in the same way that JavaBeans can, They are prepackaged pieces of application functionality that are designed to run in an application server.
JavaBeans component model defines a standard mechanism to develop portable, Java components, such as widgets or controls.
JavaBeans technology can be used in any visual Java technology integrated development environment (IDE)

6. EJB Architecture EJB Server EJB Container EJB Client
Enterprise Java Beans
Auxiliary Systems
- JNDI, JTA,
JavaMail

7. Roles in EJB Development
EJB Developer
- Person who provides implementations of EJB classes
EJB Deployer
- Responsible for Deploying EJB’s in EJB Server
EJB Container Vendor
- Provides software to install an EJB into an EJB Server
EJB Server Vendor
- Provides an Application Framework in which to run EJB Containers
Application Developer
- Who writes client applications that uses EJB.

8. EJB Server Is a High Level Process or Application that
Manages and makes EJB Containers Visible
Provides Access to System Services
Provides Naming and Transaction Services

9. EJB Container Interface between Enterprise Java Bean and outside world
Accessing of EJB is done through Container generated methods, which in turn call the EJB methods

10. EJB Clients Is an Application, Servlet, JSP or Applet that
Find EJB Containers via JNDI
Uses EJBHome to Create or Remove EJB from Container
Uses EJBObject to Invoke Business Methods of EJB

11. Enterprise Java Beans Entity Session Bean 1. Bean Managed 1. Stateless
2. Container Managed
Session Bean
1. Stateless
2. Stateful

12. Session Vs Entity Beans
1. Performs a task for a Client
2. Associated with a particular client
3. Non Persistent and do not survive System Shutdown
Entity
1. Represents a business entity Object that exists in a persistent Storage
2. Shared by multiple clients
3. Persistent across multiple Invocations and survives System Shutdown

13. Passivation and Activation
Passivation - Saving the state of a Bean to a persistent Storage Device and swapping it out
Activation - Restoring the state of Bean from a persistent Storage Device and swapping it in
Depends upon Container Provider
Applies to both Session and Entity Beans

14. Stateless Vs Stateful Session Beans
1. Posses State during Client-Bean Session
2. Is passivated
3. One Per Client
Stateless
1. No State during Client-Bean Session
2. Is not passivated
3. Can be shared by multiple clients

15. SessionBean Interface
public abstract interface SessionBean extends EnterpriseBean{
public void setSessionContext(SessionContext ctx) throws EJBException, java.rmi.RemoteException
public void ejbRemove() throws EJBException, java.rmi.RemoteException
public void ejbActivate() throws EJBException, java.rmi.RemoteException
public void ejbPassivate() throws EJBException, java.rmi.RemoteException }

16. Writing a Session Bean-Step 1
Create a Remote Interface
- Should extend EJBObject
- Provide the Business methods
- Arguments and Return types must be valid RMI types
- The throws Clause of the Business methods must include java.rmi.RemoteException

17. Writing a Session Bean-Step 2
Create Home Interface
- Should extend EJBHome
- The argument and return types of create method(s) must be valid RMI types
- create method(s) should return the Remote Interface
- Throws clause of create method(s) must include java.rmi.RemoteException and javax.ejb.CreateException

18. Writing a Session Bean-Step 3
Writing the Bean Class (SessionBean)
- should implement SessionBean interface
- Should be a public class, and cannot be abstract or final
- contains public constructor with no Arguments
- should implement ejbCreate methods whose arguments should correspond to create methods of Home Interface
- Return type of ejbCreate methods should be void
- throws clause of ejbCreate methods should implement javax.ejb.CreateException
- implements Business Methods of Remote Interface

19. Writing an EJB Client Locate the Home Interface
Create an Enterprise Bean Instance
Invoke a Business Method upon the Enterprise Bean
Remove the Bean

20. Life Cycle of Stateful SessionBean

21. Life Cycle of Stateless SessionBean

22. Container Vs Bean Managed EntityBean
1. Bean is responsible for saving its own state
2. Entity Bean consists Code for DB calls
3. Some times the code Contains DB specific calls which makes non portable
Container-Managed EntityBean
1. Container is responsible for Saving the state of Bean
2. In DD, Specify the Container managed fields
3. Is Independent of Data Store, Such as a Relational Database

23. EntityBean Interface
public abstract interface EntityBean extends EnterpriseBean{
public void setEntityContext(EntityContext ctx) throws EJBException,
java.rmi.RemoteException
public void unsetEntityContext() throws EJBException,
public void ejbRemove() throws RemoveException, EJBException,
public void ejbActivate() throws EJBException, java.rmi.RemoteException
public void ejbPassivate() throws EJBException, java.rmi.RemoteException
public void ejbLoad() throws EJBException, java.rmi.RemoteException
public void ejbStore() throws EJBException, java.rmi.RemoteException }

24. Writing a Entity Bean - Step 1
Create a Remote Interface
- Should extend EJBObject
- Provide the Business methods
- Arguments and Return types must be valid RMI types
- The throws Clause of the Business methods must include java.rmi.RemoteException

25. Writing a Entity Bean - Step 2
Create Home Interface
- Should extend EJBHome
- The argument and return types of create method(s) must be valid RMI types
- create method(s) should return the Remote Interface
- Throws clause of create method(s) must include java.rmi.RemoteException and javax.ejb.CreateException

26. Writing a Entity Bean - Step 3
Writing the Bean Class (EntityBean)
- should implement EntityBean interface
- Should be a public class, and cannot be abstract or final
- contains public constructor with no Arguments
- should implement ejbCreate and ejbPostCreate method(s) whose arguments should correspond to create method(s) of Home Interface
- Return type of ejbCreate method(s) is Primarykey
- Return type of ejbPostCreate method(s) is void
- throws clause of ejbCreate methods should implement javax.ejb.CreateException
- implements Business Methods of Remote Interface

27. Life Cycle of Entity Bean

28. Deployment of EJB’s in J2EE Server

29. Transactions
Transactions are units of work that can maintain a reliable data source that is accessed by several clients.

30. Transactions Transactions have ACID Properties
Atomicity: A transaction either commits or aborts
Consistency: A transaction correctly manages the changing state of a system
Isolation: A transaction’s effects are isolated from other transactions’ effects
Durability: The result of a transaction persists

31. Java Transaction Service (JTS)
JTS is an implementation of an underlying transaction service
javax.transaction.TransactionService allows the application server to manage transaction boundaries.

32. EJB Transactions EJB Architecture: Supports flat transactions
Supports the two-phase commit protocol
Prepare-ready
Commit
Supports access to transaction service using the JTS interface.

33. UserTransaction Interface
javax.transaction.UserTransaction
begin
commit
rollback
setRollbackOnly
setTransactionTimeOut
getStatus

34. Container-Managed Isolation
Enterprise Bean can still participate via the EJBContext
The setRollbackOnly method is used by a Bean to force a rollback (usually due to an application exception).
The getRollbackOnly method is used by a Bean to test if the transaction is marked for a rollback.

35. Bean-Managed Isolation
Session Bean Can:
Gain Access to the transaction service
Define transaction type as Bean in the deployment descriptor
Ensure methods do not declare attributes that conflict with Bean-Managed demarcation.
Use the javax.transaction.UserTransaction interface.
Start a new transaction only after others complete

36. Bean-Managed Isolation
import javax.transaction.UserTransaction;
public class CartBean implements SessionBean{
EJBContext ic = null; // initialize some where else
void someMethod(){
UserTransaction ex = ic.getUserTransaction();
tx.begin();
// do work
tx.commit(); }

37. Bean-Managed Isolation
Use the following methods:
UserTransaction.getStatus method obtains status of a global transaction
UserTransaction.rollback method rolls back a global transaction
Do not use the following methods:
setRollbackOnly()
getRollbackOnly()

38. Bean-Managed Demarcation
Stateful Session Beans
Methods can return in the middle of a transaction without closing the transaction.
Subsequent calls can go to any Bean method
Stateless and Entity Beans
Methods must complete a transaction before returning.

39. Vendors Supporting EJB
SUN
IBM
WebLogic
Oracle
Inprise
BEA
Novell
Netscape
IONA
Gemstone
Informix
Allaire