EJB Session Beans

1
EJB Session Beans

• Controlling your application
• (the business logic)

2
What you need to know

• Advantage of using Session EJBs
• Guidelines for their use
• Know the Session EJB pattern
• Define and describe the role of a Java Interface
  class
• Stateful vs. stateless EJBs
• Passivation vs. activation
• Remote vs. local interface
• Bean vs. container managed Session EJBs
• Naming directory services and JNDI
• Algorithm for using Session EJBs
• Develop an application using Session EJBs and
  describe the function of each statement in the
  program.

3
Advantages

• Automatic Transaction management
• Resource management
• Security

4
Basic EJB Pattern
ltltEJBgtgt
Bean(Implementation)
Implementation
Client Interface
5
Full Internal View
ltltEJB Session BeangtgtOrderControl
Client Interface
Implementation
6
Remote vs. Local Entity Beans

• Remote Session EJB
• Anywhere on the network
• Pass by value
• Local EJB are faster but not as flexible,
  scalable and adaptable
• On same server as Session Beans
• No network traffic
• Pass by reference

7
Stateful vs. Stateless Transactions

• A stateless transactions is
• Usually a one step transaction
• Does not the save transaction state data
• No memory is allocated in the pool for each
  session with a client
• EJB is never passivated or activated
• Stateful transaction
• Used for multi-step transactions
• Saves state data for each client session
• Memory is allocated in pool for each client
  session
• EJB is passivated and activated

8
Stateless Session Bean LifeCycle
Does not exist
Class.newInstance(), _at_PostConstruct
Ready in pool
Business method
9
Stateful EJB Session Bean Lifecycle
10
Locating an EJB

• EJBs can be remote anywhere on the network
• Must use a directory service and DNS to locate
  network objects
• JNDI (Java Naming Directory Interface)
• Programming interface to the directory services
  to locate any object in a network (files, EJBs,
  web services, etc.)

11
Directory Service names

• Most use X.500 naming standard
• c (country name)
• o (organizationName)
• ou (organizationUnitName)
• l (localityName)
• cn (commonName)
• dc (domainComponent)
• uid (userid)
• Each type of directory service has its own
  naming syntax
• LDAP example
• cnMartin Bond, ouAuthors, oSAMS, cus
• Microsoft Active Directory Service
• cnMartin Bond/ouAuthors/oSAMS/cus

12
JNDI names

• JNDI names are not specific to directory services
  
• JNDI maps universal name to specific directory
  service syntax
• Typical JNDI name
• SAMS/authors/Martin Bond

13
Guidelines for use

• Coarse-Grained better than Finely-Grained
• Use stateless whenever possible
• Use the remote interface for flexibility

14
Outline for using remote EJBs

• Get initial naming context for EJB
• Use JNDI to lookup and find reference to object
• Create a client session for the EJB
• (returns remote interface)
• Call business methods defined in the remote
  interface

15
Locate a Remote Session EJB
try InitialContext initialContext new
InitialContext() // get jndi context String
jndiName BusinessRulesBean.RemoteJNDIName //
get jndi name // lookup and get remote
interface for session bean
BusinessRulesRemote businessRulesRemote
(BusinessRulesRemote)
initialContext.lookup(jndiName )
catch (NamingException ne) throw new
MyAppException(ne.getMessage())
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Calling business methods
try InitialContext initialContext new
InitialContext() // get jndi context String
jndiName BusinessRulesBean.RemoteJNDIName //
get jndi name // lookup and get remote
interface for session bean
BusinessRulesRemote businessRulesRemote
(BusinessRulesRemote)
initialContext.lookup(jndiName ) // call
any business methods defined in the interface
Person person businessRulesRemote.login(usernam
e, password) catch (Exception ne)
throw new MyAppException(ne.getMessage())