1. Enterprise Java Beans Overview
EJB Intro

2. Agenda Background EJB Overview Bean Types EJB Interfaces and Classes
EJB Intro

3. Applications Web Applications (Servlets/JSPs)
Provided user interface
access to database
simple business logic
no transactions except at the database level; no distributed transactions across business logic
Distributed Applications (RMI)
Distributed access to business logic
access to, but no direct support for database
limited transactions
We have to write a lot of ‘plumbing’ code v
EJB Intro

4. What didn’t we address ? Could someone else deploy your application?
Component reusability
Security
Threading
Resource Management
Load-Balancing
Fault Tolerance (a little with activation) v
EJB Intro

5. Paradigm Shift
We need to start thinking of applications as a set of reusable components and some business logic that ties the components together
Deployed in a re-usable environment that handles middleware and deployment requirements v
EJB Intro

6. Components Vs. Objects Usually larger-grained
Provide a complete capability
Credit Card Verification
Can be customized for deployment v
EJB Intro

7. Component Architectures
Client-Side
Applets
Java Beans
ActiveX
Server Side
Servlets
Enterprise Java Beans (EJB)
CORBA Components
Microsoft .NET v
EJB Intro

8. Distributed Objects Makes business objects more accessible
permits more of an 3-tier architecture
user interface at the first tier (Web Applications)
business logic at the second tier (Business Applications)
enterprise resources at the third tier (Databases)
Key technologies include RMI, CORBA, and DCOM
Provide for communication, but limited in server-side component support; results in “roll your own” component models v
EJB Intro

9. Server-Side Components
Architecture for developing distributed business objects
Separates the development from the assembly into specific applications
allows for the sale of smaller/reusable components rather than end-to-end systems
assembler determines actual transactional, security, persistence behavior, etc. for the component. v
EJB Intro

10. Component Transaction Monitors (CTMs)
Sophisticated distributed object Application Servers
usually made up of web servers, ORBs, Messaging, Databases, Naming, etc.
Hybrid of TP Monitors (e.g., CICS and Tuxedo)and ORBs (e.g., CORBA and RMI)
Provide infrastructure for managing transactions, object distribution, concurrency, security, persistence, and resource management
the developer isn’t left “rolling their own”
the developer complies with the model and basically implements a lot of callback event and declarative programming
Analogy: CD-player = CTM, CD = Server-side Component v
EJB Intro

11. Enterprise JavaBeans (EJBs)
Standard server-side component model for Java Enterprise Applications
Enables large scale development
Helps build portable applications
Has nothing to do with “JavaBeans”
JavaBeans designed for intra-process purposes
GUIs
non-visual widgets
Enterprise Java Beans (EJB) designed for inter-process purposes v
EJB Intro

12. EJB Server-side Component Model
Encapsulates application’s business logic
manage terms of an account
manage state of an order
provide tax calculations
Normally accesses database or other backend systems
EJB Clients
implement only the presentation logic
use EJBs for their business logic v
EJB Intro

13. EJB Enables Large System Development
Distributed communication
RMI, RMI-IIOP, CORBA-IDL
Transaction management
scope, isolation, lifecycle
Resource pooling
separation of bean state from object state
Security
class/method level, role based
Threading
container initiated
Persistence
container and bean managed v
EJB Intro

14. EJB Resource Pooling Bean State connection Object Methods()
getCounty()
getVotingDistrict()
Bean Instance
Bean Methods()
ejbCreate()
ejbActivate()
ejbPassivate()
ejbRemove()
setEJBContext()
unsetEJBContext()
Object State
name
address
Entity Beans
Only
Object State
Object State
Object State
Bean Pool
Bean Instance
Bean Instance
Database
Bean Instance v
EJB Intro

15. EJB Portability Java EJB components platform independence
“write once, run anywhere”
EJB components
platform/implementation independence
write once, run in any Application Server complying with the EJB spec
J2EE reference implementation
IBM’s Websphere
BEA’s Weblogic Server
Borland’s Enterprise AppServer
... v
EJB Intro

16. EJB Architecture Interfaces and Classes Container Application Server
beans
entity bean
session session (no primary key)
Stateless session bean
Stateful session bean
message driven bean (no primary key, home or object interface)
primary key (entity beans only)
home interface (local and remote)
EJB object interface (local and remote)
Container
Application Server v
EJB Intro

17. Bean Types Entity beans Session beans
models persistent state - this state is maintained through all method and server invocations
nouns of the domain
real world objects (e.g. Owner, Account, Transaction)
Session beans
models non-persistent state - this state will be lost between method invocations (stateless session) or server invocations (Stateful session)
manage tasks performed on behalf of a single client (e.g. Teller, Monthly Statement)
contains the business processes in which to use entity beans
manages actions that may cross entity beans or go outside the concern of an entity bean
e.g. Teller may authenticate the user and transfer funds between accounts
e.g. Statement may include transactions from multiple accounts v
EJB Intro

18. Bean Types (cont.) Message Driven beans
models non-persistent state - this state will be lost between message processing
similar to Stateless Session Beans (which are invoked through synchronous RMI calls)
invoked through asynchronous JMS Messages v
EJB Intro

19. Bean Usage Entity beans Session beans
model state maintained across all client interactions
represent a row of data in a database
Session beans
model business process being performed by a single client involving one or more entity beans
it extends the actions of the client into the server
simplifies the actions programmed by the client
limits the number of distributed calls required between the client and the entity beans
limits the number of stubs that have to be loaded by the client
are not persisted to a database v
EJB Intro

20. Bean Usage (cont.) Message Driven Bean
model business process invoked through asynchronous messages
are not persisted to a database v
EJB Intro

21. Stateful and Stateless Session Beans
Stateful session bean
maintain the conversational state between a client and the session bean
may be serialized out and passivated to conserve system resources
will be serialized in and activated when needed in the future
e.g. Teller session bean who is logged into an transfers funds between accounts
Stateless session bean
do not maintain conversational state
each method is independent of another and the only information needed is is supplied in the call parameters
e.g. Statement that is given a list of accounts or an owner to generate a textual report for
consumes the least amount of resources among all the bean types v
EJB Intro

22. Stateless Session Bean Lifecyclev
EJB Intro

23. Stateless Session Bean Conceptual Class Modelv
EJB Intro

24. Stateful Session Bean Lifecyclev
EJB Intro

25. Stateful Session Bean Conceptual Class Modelv
EJB Intro

26. Entity Bean Lifecycle v
EJB Intro

27. Entity Bean Conceptual Class Modelv
EJB Intro

28. Message Driven Bean Lifecycle
EJB Intro

29. Message Driven Bean Conceptual Class Model
EJB Intro

30. EJB Classes and Interfaces
Cabin Example from “Enterprise Java Beans, 3rd Edition”, Monson-Haefel v
EJB Intro

31. Remote Interface Called “the EJB Object”
Defines the “business” methods that will be available to clients in a distributed call
e.g. Account.debit(transactionRec)
e.g. Teller.transfer(sourceAccount, targetAccount)
Gets compiled by the ejb compiler to creates RMI stubs and skeletons
stubs are used by RMI to translate a method invocation to wire format
skeletons are used by RMI to translate wire format to a method invocation v
EJB Intro

32. Remote Interface (cont.)
Defined as a Java interface
extends javax.ejb.EJBObject
extends java.rmi.Remote
getEJBHome() - returns the Home object for the bean
getPrimaryKey() - returns the primary key for the object
getHandle() - returns a handle to object that may be used to re-establish communications at a later time; possibly in another server
remove() - removes this EJBObject object (prior to eviction)
isIdentical(EJBObject) - returns if both objects are same v
EJB Intro

33. Remote Interface Example: Cabin
package com.titan.cabin;
import java.rmi.RemoteException;
public interface Cabin extends javax.ejb.EJBObject {
public String getName() throws RemoteException;
public void setName(String str) throws RemoteException;
public int getDeckLevel() throws RemoteException;
public void setDeckLevel(int level) throws RemoteException;
public int getShip() throws RemoteException;
public void setShip(int sp) throws RemoteException;
public int getBedCount() throws RemoteException;
public void setBedCount(int bc) throws RemoteException; } v
EJB Intro

34. Local Interface (EJB 2.0)
Like the Remote Interface, defines the “business” methods that will be available to clients, but only for local calls
e.g. Account.debit(transactionRec)
e.g. Teller.transfer(sourceAccount, targetAccount)
Can only be used within the same JVM as the EJB
Gets compiled by the ejb compiler to creates local stubs for container to interpose transactions, access control, etc. on invocations. v
EJB Intro

35. Local Interface (EJB 2.0) (cont.)
Defined as a Java interface
extends javax.ejb.LocalObject
getEJBLocalHome() - returns the LocalHome object for the bean
getPrimaryKey() - returns the primary key for the object
remove() - removes this EJBObject object (prior to eviction)
isIdentical(EJBObject) - returns if both objects are same
not applicable
extends java.rmi.Remote - it is a local object
getHandle() - unnecessary since client/EJB in same JVM
methods do not throw RemoteException; only EJBException v
EJB Intro

36. Local Interface Example (EJB 2.0): Cabin
package com.titan.cabin;
import javax.ejb.EJBException;
public interface LocalCabin extends javax.ejb.EJBLocalObject {
public String getName() throws EJBException;
public void setName(String str) throws EJBException;
public int getDeckLevel() throws EJBException;
public void setDeckLevel(int level) throws EJBException;
public int getShip() throws EJBException;
public void setShip(int sp) throws EJBException;
public int getBedCount() throws EJBException;
public void setBedCount(int bc) throws EJBException; } v
EJB Intro

37. Remote Home Interface
Defines the “lifecycle” methods that will be available to clients in a distributed call
create new bean objects, locate or remove existing bean objects
e.g. AccountHome.create(owner, initialBalance)
e.g. AccountHome.findByPrimaryKey(accountId)
e.g. TellerHome.create(login, pin)
e.g. MonthlyStatementHome.create()
Gets compiled by the ejb compiler to creates RMI stubs and skeletons v
EJB Intro

38. Remote Home Interface (cont.)
Defined as a Java interface
extends javax.ejb.EJBHome
extends java.rmi.Remote
getEJBMetaData() - returns metadata about the bean
remove(primaryKey) - removes object identified by primary key
remove(handle) - removes object identified by its EJBHandle
defines
create methods (create(<XXXX>))
finder methods (findBy<XXXX>(<YYYY>))
home methods (<XXXX>) //EJB 2.0 v
EJB Intro

39. Remote Home Interface Example: CabinHome
package com.titan.cabin;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.FinderException;
public interface CabinHome extends javax.ejb.EJBHome {
public Cabin create(int id)
throws CreateException, RemoteException;
public Cabin findByPrimaryKey(CabinPK pk)
throws FinderException, RemoteException;
public int getDeckCount(int deck)
throws RemoteException;//EJB2.0 } v
EJB Intro

40. Local Home Interface (EJB 2.0)
Like the Remote Home Interface, defines the “lifecycle” methods that will be available to clients in a distributed call
create new bean objects, locate or remove existing bean objects
e.g. AccountHome.create(owner, initialBalance)
e.g. AccountHome.findByPrimaryKey(accountId)
e.g. TellerHome.create(login, pin)
e.g. MonthlyStatementHome.create()
Can only be used within the same JVM as the EJB
Gets compiled by the ejb compiler to creates stubs for container interpose on invocations v
EJB Intro

41. Local Home Interface (cont.)
Defined as a Java interface
extends javax.ejb.EJBLocalHome
remove(primaryKey) - removes object identified by primary key
not applicable
extends java.rmi.Remote
getEJBMetaData() - inserted in Remote Home for visual tools only
remove(handle) - no need for handles in local JVM
defines
create methods (create(<XXXX>))
finder methods (findBy<XXXX>(<YYYY>))
home methods (<XXXX>) v
EJB Intro

42. Local Home Interface Example (EJB 2.0): CabinHome
package com.titan.cabin;
import javax.ejb.EJBException;
import javax.ejb.CreateException;
import javax.ejb.FinderException;
public interface LocalCabinHome
extends javax.ejb.EJBLocalHome {
public LocalCabin create(int id)
throws CreateException, EJBException;
public LocalCabin findByPrimaryKey(CabinPK pk)
throws FinderException, EJBException;
public int getDeckCount(int deck)
throws EJBException; } v
EJB Intro

43. Bean Class
Implements the business methods defined in the Object interface
does not inherit from the Object or Home interfaces
must have methods that match signatures supplied in all of the Object interface and portions of the Home interface
Account.deposit(transactionRec) - AccountBean.deposit(transarctionRec)
AccountHome.create(owner) - AccountBean.ejbCreate(owner)
the connection between the Object/Home interface calls and the Bean implementation is done by the EJB compiler that creates the container-specific skeletal code
uses the Deployment Descriptor to help generate glue code
similar in functionality to a C++ template or a CORBA TIE class v
EJB Intro

44. Bean Class (cont.) Clients never interact with bean classes themselves
always interact with the bean through home (create, find, remove) and remote/local interfaces (business methods)
beans that interact with other beans are simply clients of the other bean
stubs and skeletons are created from the interfaces that glue the client, the database, and the bean code together v
EJB Intro

45. Bean Class (cont.)
implements javax.ejb.[Entity|Session|MessageDriven]Bean
extends empty javax.ejb.EnterpriseBean; extends java.io.Serializable
set/unset[Entity|Session|MessageDriven]Context()
provides callback into container to find caller id, transaction information, etc.
ejbCreate()
container calls this when the bean gets associated with an object
ejbPostCreate() [ Entity Beans Only ]
container calls this after persisting the object’s state v
EJB Intro

46. Bean Class (cont.) ejbPassivate() [ Session and Entity Beans Only]
container calls this method when the instance of the bean class is either being returned to the pool (Entity) or serialized/unloaded (Stateful)
ejbActivate() [ Session and Entity Beans Only]
container calls this method when the instance of the bean class is taken from a pool of available instances and associated with a particular EJB Object (Entity) or loaded/de-serialized (Stateful)
ejbRemove()
container calls this method of an instance before removing an EJB Object from the system v
EJB Intro

47. Bean Class (cont.) ejbLoad() [ Entity Beans Only ]
container calls this method to instruct the instance to synchronize its state with the state stored in the database
command (bean managed), completion event (container managed)
ejbStore() [ Entity Beans Only ]
container calls this method to instruct the instance to synchronize the state store in the database with its state
command (bean managed), preparation event (container managed) v
EJB Intro

48. Bean Class (cont.)
onMessage(Message msg) [ Message Driven Beans Only ]
container calls bean method to handle message from Destination (Topic or Queue) v
EJB Intro

49. Bean Class Example (EJB 2.0): CabinBean
package com.titan.cabin;
import javax.ejb.EntityContext;
public abstract class CabinBean implements javax.ejb.EntityBean {
public abstract void setId(Integer id);
public abstract Integer getId();
public abstract void setName(String name);
public abstract String getName();
public abstract void setDeckLevel(int level);
public abstract int getDeckLevel();
public abstract void setShipId(int ship);
public abstract int getShipId();
public abstract void setBedCount(int count);
public abstract int getBedCount(); v
EJB Intro

50. Bean Class Example (EJB 2.0): CabinBean (cont.)
public Integer ejbCreate(int id){
this.setId(new Integer(id));
return null; }
public void ejbPostCreate(int id){
// Do nothing. Required.
//EJB 2.0 Home Method
public int ejbGetDeckCount(int deck) {
int count=0;
//implementation not shown
return count; v
EJB Intro

51. Bean Class Example (EJB 2.0): CabinBean (cont.)
public void setEntityContext( // Not implemented. }
public void unsetEntityContext(){ // Not implemented.
public void ejbActivate(){ // Not implemented.
public void ejbPassivate(){ // Not implemented.
public void ejbLoad(){ // Not implemented.
public void ejbStore(){ // Not implemented.
public void ejbRemove(){ // Not implemented. v
EJB Intro

52. Bean Class Example (EJB 1.1): CabinBean
package com.titan.cabin;
import javax.ejb.EntityContext;
public class CabinBean implements javax.ejb.EntityBean {
public Integer id;
public String name;
public int deckLevel;
public int shipId;
public int bedCount; v
EJB Intro

53. Bean Class Example (EJB 1.1): CabinBean (cont.)
public String getName(){ return name; }
public void setName(String str){ name = str; }
public int getShipId(){ return shipId; }
public void setShipId(int sp) { shipId = sp; }
public int getBedCount(){ return bedCount; }
public void setBedCount(int bc){ bedCount = bc; }
public int getDeckLevel(){ return deckLevel; }
public void setDeckLevel(int level){ deckLevel = level } v
EJB Intro

54. Bean Class Example (EJB 1.1): CabinBean (cont.)
public Integer ejbCreate(int id){
this.id = new Integer(id);
return null; }
public void ejbPostCreate(int id){
// Do nothing. Required. v
EJB Intro

55. Bean Class Example (EJB 1.1): CabinBean (cont.)
public void setEntityContext( // Not implemented. }
public void unsetEntityContext(){ // Not implemented.
public void ejbActivate(){ // Not implemented.
public void ejbPassivate(){ // Not implemented.
public void ejbLoad(){ // Not implemented.
public void ejbStore(){ // Not implemented.
public void ejbRemove(){ // Not implemented. v
EJB Intro

56. Primary Key Class
Value that uniquely identifies the object in the database
Implements java.io.Serializable
Implemenets
hashCode()
equals()
toString() helpful
Contains identical public attributes from the Bean Class for those that represent the bean’s primary key value(s). v
EJB Intro

57. Primary Key Class Example: CabinPK
package com.titan.cabin;
public class CabinPK implements java.io.Serializable {
public int id;
public int hashCode( ){
return id; }
public boolean equals(Object obj){
if(obj instanceof CabinPK){
return (id == ((CabinPK)obj).id);
return false;
public String toString(){
return String.valueOf(id); v
EJB Intro

58. Containers Manages interaction between the bean and its server
Provides a uniform interface to the bean and to the server v
EJB Intro

59. Containers (cont.)
Creates new instances of beans and manages their persistence
provides mapping between bean and container’s underlying database
provides the skeletal class code for the home and remote interfaces
e.g. AccountHome.findByPrimaryKey(accountPK)
container supplies code to create row in database, instantiate an EJB Object to represent that instance of an account
e.g. AccountHome.remove(accountPK)
container supplies code to remove row in database and remove any existing EJB Objects
e.g. Account.debit(transactionRec)
container supplies code obtain the EJB Object from storage, locate a bean to take on its state, and invoke behavior on the bean v
EJB Intro

60. Deployment Descriptor
Instructs the server on the type of bean (session or entity)
Instructs the server how to apply services to the bean
Described in XML
Created from IDE or text source
Supplied with other bean components in a “jar” (Java archive) file
bean class
remote interface
home interface
primary key (for entity beans)
deployment descriptor
RMI stub/skeleton v
EJB Intro

61. Deployment Descriptor Example: ejb-jar.xml (Cabin)
<?xml version="1.0" ?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "
<ejb-jar>
<enterprise-beans>
<entity>
<description>
This Cabin enterprise bean entity represents a cabin on a cruise ship.
</description> v
EJB Intro

62. Deployment Descriptor Example: ejb-jar.xml (Cabin)
<ejb-name>CabinBean</ejb-name>
<home>com.titan.cabin.CabinHome</home>
<remote>com.titan.cabin.Cabin</remote>
<local-home>com.titan.cabin.LocalCabinHome</local-home>
<local>com.titan.cabin.LocalCabin</local>
<ejb-class>com.titan.cabin.CabinBean</ejb-class>
<persistence-type>Container</persistence-type>
<prim-key-class>java.lang.Integer</prim-key-class>
<reentrant>False</reentrant> v
EJB Intro

63. Deployment Descriptor Example: (cont.)
<cmp-version>2.x</cmp-version>
<abstract-schema-name>Cabin</abstract-schema-name>
<cmp-field> <field-name>id</field-name> </cmp-field>
<cmp-field> <field-name>name</field-name> </cmp-field>
- <cmp-field> <field-name>deckLevel</field-name> </cmp-field>
<cmp-field> <field-name>shipId</field-name> </cmp-field>
- <cmp-field> <field-name>bedCount</field-name> </cmp-field>
<primary-field>id</primary-field>
</entity>
</enterprise-beans>
...
</ejb-jar> v
EJB Intro

64. EJB Object class
Written by the container-specific compiler after processing the deployment descriptor
Implements methods defined in remote interface by delegating them to an instance of the bean class
EJBObject
getEJBHome( )
getPrimaryKey(
getHandke()
remove( )
isIdentical( )
<<Interface>>
Account
debit( )
credit( )
getBalance(
Account_EJBObject
AccountBean
id_
balance_
ejbCreate (balance)
ejbPostCreate (balance)
ejbPassivate ()
ejbActivate ()
ejbLoad ()
ejbStore ()
ejbRemove ()
setEntityContext ()
unsetEntityContext ()
EntityBean
ejbPassivate( )
ejbActivate( )
ejbLoad( )
ejbStore( )
ejbRemove( )
setEntityContext( )
unsetEntityContext( )
<<extends>>
<<implements>> v
EJB Intro

65. EJB home class
Written by the container-specific compiler after processing the deployment descriptor
Implements methods defined in home interface
locate
create
remove
Handles interactions with resources pools, persistence mechanism, and resource managers v
EJB Intro

66. Example Client Context jndiContext = getInitialContext();
Object obj = jndiContext.lookup("ejb/CabinHome");
System.out.println("found it! ="+ obj);
CabinHome home = (CabinHome)javax.rmi.PortableRemoteObject.narrow(obj, CabinHome.class);
System.out.println("narrowed it! ="+ home);
Cabin cabin_1 = home.create(1);
System.out.println("created it! ="+ cabin_1);
cabin_1.setName("Master Suite");
cabin_1.setDeckLevel(1);
cabin_1.setShip(1);
cabin_1.setBedCount(3); v
EJB Intro

67. Example Client CabinPK pk = new CabinPK(); pk.id = 1;
System.out.println("keyed it! ="+ pk);
Cabin cabin_2 = home.findByPrimaryKey(pk);
System.out.println("found by key! ="+ cabin_2);
System.out.println(cabin_2.getName());
System.out.println(cabin_2.getDeckLevel());
System.out.println(cabin_2.getShip());
System.out.println(cabin_2.getBedCount()); v
EJB Intro

68. Usage Scenarios v
EJB Intro

69. Creating an Account Object
AccountBean
database
AccountBean
3: select instance
8: return instance
AccountBean
5: insert
bean pool
4: ejbCreate(10.00)
6: ejbPostCreate(10.00)
7: ejbPassivate()
1: createAccount(10.00)
AccountHome_EJBHome
remote interface
2: new Account_EJBObject
Client
Account_EJBObject
AccountBean v
EJB Intro

70. Accessing an Account Object
AccountBean
database
AccountBean
3: select instance
10: return instance
AccountBean
2: select
8: update
bean pool
4: populate state
5: ejbLoad()
6: debit(10.00)
7: ejbStore()
Client
Account_EJBObject
AccountBean
1: debit(10.00) v
EJB Intro

71. Deleting an Account Object
AccountBean
database
AccountBean
3: select instance
10: return instance
2: select
7: delete
AccountBean
bean pool
4: populate state
5: ejbLoad()
6: ejbRemove()
1: remove(pKey)
AccountHome_EJBHome
8: remove()
Client
Account_EJBObject
AccountBean v
EJB Intro

72. Questions to Ponder...
Entity bean, stateful session bean, stateless session, message driven bean?
object which requires access by multiple clients over its lifetime
object whose work accepts and returns all information in the call
object whose work arrives through an asynchronous message
object that sends asynchronous messages
object that must exist after server crash
object that must exist between method invocations
object that encapsulates a set of client actions to multiple beans
Why is there not a ratio of 1:1 between instanced of beans (EJB Objects) and instances of the bean class?
What GoF Pattern does this depict?
Name that bean
entity - session beans have only a single client
stateless session
entity - only type persisted
statful session or entity bean, except that the entity bean doesn’t maintain a per-client context outside of a transaction
session bean - either
Scalability
Flyweight and Proxy/Decorator - the bean class is the flyweight and the remote interface is a proxy/decorator that knows to have the state activated inside the flyweight v
EJB Intro