Course

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Course 3036Enterprise Java Beans

• Patrick W. McMichael
• Pillar Technology Group, LLC

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Your Expectations

• Who are you? Where are you from? What is your
  role?
• Why are you here at this tutorial?
• What business challenges are you hoping J2EE can
  help with?

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My Expectations

• NO head-nodding -- if in doubt, ASK!
• DONT be shy! Im going to need your help this
  afternoon!
• Think about how the concepts presented might be
  applied in your domain.

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Agenda

• The role of the container
• Bean Basics
• A Closer Look
• Entity Beans
• Session Beans
• Message Driven Beans
• Bean Info You Shouldnt Leave Home Without
• JNDI
• JNDI ENC
• Transactions
• Exceptions
• Coming Soon to a Container Near You! (EJB 2.1/3.0)

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eFlix Online Rental System
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eFlix Online Rental System
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7 Primary Services (Monson-Haefel)

• Concurrent access to system resources
• Transaction management
• Persistence
• Object distribution / Location transparency
• Naming / Object binding
• Security
• Asynchronous messaging

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Tell Me About It!
How have your apps depended on these services?
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Approach 1 -- The MACHO Way
I coded my app

• with vi
• by candlelight
• on the last ounce of laptop battery juice
• barefoot
• using a dial-up connection

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Approach 2 The time-to-market way
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How do you configure / manage these services?

• Programmatically
• Declaratively
• UUM Example
• intranet deployment
• extranet deployment

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Questions

• Whats the point of using a J2EE container? What
  does it buy you?
• Whats the advantage of declarative configuration
  of an apps behavior vs. programmatic
  configuration?

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Bean Basics
EXAMPLE The Rental Manager EJB
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Break That Bean Down!

• RentalManagerHome
• RentalManager
• RentalManagerBean
• Developer Written Code vs. Generated Code
• javac vs. EJB Compiler

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WHY All These Classes?

• Remember the primary services?
• Example Going on a Date

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Client Calls to Session/Entity Beans
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The Special Case of the MDB
Hey You!
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Remote vs. Local Interfaces

• The expense of RMI, Serialization, etc.
• Proprietary Optimizations
• Planned Localization

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Remote vs. Local Interfaces --Delegated Calls
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Remote vs. Local Interfaces --Session Façade w/
Entity Beans
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Questions

• Which parts of an EJB does a developer have to
  create?
• Whats the point of the egg yolk/eyeball
  diagram?
• Whats unique about MDBs?
• Whats the difference between remote and local
  interfaces?
• When would you use one, the other, or both?

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Bean Types
Entity Beans
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Entity Beans

• Encapsulate key NOUN entities in the problem
  domain
• eFlix Entity Bean Candidates
• Persistence -- CMP vs. BMP
• CMR -- introduced in EJB 2.0
• EJB QL -- also brought in by the 2.0 spec
• (shameless plug for 3138)

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Entity Bean Example

• TitleHome -- Local Home Interface
• create methods
• find methods
• remove
• Title -- Local Business Interface
• getters
• setters
• TitleBean -- Bean Implementation Class
• ejbCreate counterparts to Home Interface
• lifecycle/callback method implementation
• getters/setters and the abstract persistence
  schema

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Entity Bean CMR Example
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Entity Bean Example -- EJB QL

• EJB 2.0s EJB QL provides a non-proprietary,
  declarative way of mapping custom finders (i.e.
  not by primary key) to their implementation.
• findUnitsForTitleByStatus method on TitleUnitHome
• SELECT OBJECT(u) FROM TitleUnit AS u WHERE
  u.title.productNumber ?1 AND u.status ?2

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Entity Bean Example -- EJB QL

• SELECT OBJECT(u) FROM TitleUnit AS u WHERE
  u.title.productNumber ?1 AND u.status ?2
• TitleUnit -- Abstract Schema Name
• u -- AS clause, object usage, references
• u.status -- drill down to field value
• u.title.productNumber -- carry across CMR objects

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The Entity Bean Lifecycle
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Entity Beans vs. Straight JDBC

• Simultaneous access to large volumes of entities
  -- POOL EXAMPLE -- NEED MORE OR LESS WILLING
  VOLUNTEERS!
• Simultaneous access to same data at the same time
  by multiple clients (potential blocking issues)
• Optimistic Concurrency
• DB Schema -- stable or still in flux?
• Session Façade Pattern -- clients shouldnt know
  or care if entity beans JDBC, JDO, Hibernate,
  etc. was used.

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Bean Types
Session Beans
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Session Beans

• Handle things like...
• business logic
• workflow
• Come in two varieties
• Stateless
• Stateful

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Session Beans
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Stateless Session Bean Lifecycle
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Stateful Session Bean Lifecycle
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Stateless Session Bean Advantages

• NO Activation/Passivation
• Instance Swapping between clients
• fewer beans can service more clients!
• Simple, Efficient Failover in a clustered
  environment

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Session Bean Example

• TitleManager Home Interface
• create method
• TitleManager Business Interface
• business methods
• TitleManager Bean Class
• Session Façade Pattern
• locateAvailableUnit method in façade -- more
  specific to a business service
• findUnitsForTitleByStatus method in Entity Bean
  Home (uses EJB QL) -- more generalized

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Bean Types
Message Driven Beans
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Messaging Basics
First, a little background...
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JMS Messaging in Java --Point-to-Point
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JMS Messaging in Java --Pub-Sub
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Before MDBs...

• Session and Entity Beans were NOT designed to
  handle asynchronous processing of JMS messages.
• What about synchronous processing?
• What triggers the processing? A client call?
• What type of receiving would be done?
• Endless blocking?
• Timed blocking?
• Non-blocking?
• There simply were NO good options before MDBs!

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MDB Message Processing

• Asynchronous -- senders/publishers of messages
  are decoupled from the processing of the
  messages.
• Concurrent -- container-provided, multithreaded,
  concurrent message consumption
• Automated -- No client trigger calls are needed
  because...

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Client Calls to MDBs
The CONTAINER IS the client!
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The MDB Lifecycle
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Example 1a -- Publishing to a Topic
Renting Out Titles -- RentalManagerBean
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Example 1b --An Example Subscriber
Renting Out Titles -- CustomerRentalWorkOrderMDB
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Example 1c --Run It!
onMessage -- CustomerRentalWorkOrderMDB
CustomerRentalNotificationMDB
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MDB Message Processing

• Implements MessageDrivenBean
• Implements MessageListener
• EJB 2.1 allows other options (I.e. JAXM)
• This is why EJB 2.0 did NOT have
  MessageDrivenBean extend MessageListener
• onMessage method (JMS)
• The bean pool and MDBs
• ejb-jar.xml
• ejb-borland.xml
• jndi-definitions.xml

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Questions

• What are the 3 bean types?
• Which was new to EJB 2.0? Why was it added?
• What are the two types of session beans?
• What are the peformance differences b/t stateful
  and stateless and why?
• Whats an alternative to a Stateful session bean
  in a web application?

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Does your head hurt yet?
Bean Info You Shouldnt Leave Home Without
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JNDI Lookups of EJBs

• Java Naming and Directory Interface
• Object Binding
• LDAP
• Remote EJB Lookup Example -- RUN IT!
• initialize method in TestRentalManager
• InitialContext object
• properties (parms vs. jndi.properties)
• lookup(ltJNDI Namegt)
• narrowing remote references (the joy of RMI)

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JNDI ENC Bean Resource Dependencies
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JNDI ENC

• JNDI Environment Naming Context
• each EJBs own private Idaho namespace
• relative to javacomp/env
• subcontexts recommended by spec (ejb, jdbc, jms,
  mail, url)
• Example of JNDI ENC refs in RentalManager
• local ejb refs (TitleManager, Payment Manager)
• DataSource for connections used in DAO class
• JMSConnectionFactory objects and Destinations
• Differences in lookups (JNDI vs. JNDI ENC, remote
  vs. local)

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Transactions -- Title Rental Example

• Process each title the customer wants to rent
• find an available unit for the title
• reserve the unit
• determine the rental fee and factor into the
  running total
• Create a rental record for each title that was
  reserved
• Charge the customer for the rentals
• Publish a JMS message to the Topic for further
  (asynchronous) processing

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Transactions -- Title Rental Example

• ACID Properties
• Atomic unit of work
• Consistent state (DB, JMS Destinations)
• Isolation of work from other system activity
• Durable end result

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Transactions -- Title Rental Example

• Possible Failure points in workflow
• 2/3 titles reserved, third is unavailable
• 3 titles reserved, rental records created, but
  charge to customers credit card fails
• All work up to the JMS publish works, but the
  message never hits the Topic
• no notification to customer
• no work order to get product out the door

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Transactions -- Declarative CMT

• NotSupported -- We dont do that here.
• Supports -- If you got one, cool, otherwise, who
  cares!
• Required -- I need one, and if you dont provide
  one, Ill take care of business myself.
• RequiresNew -- I dont care if you have one or
  not. I want my own!
• Mandatory -- I want one, and you better give it
  to me!
• Never -- I dont want one, and dont even think
  of calling me with one!

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Example 2 --Run It!
rentOutTitles
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Exceptions -- Application Exceptions

• Do NOT extend java.lang.RuntimeException
• or subclasses like EJBException
• Do NOT extend java.rmi.RemoteException or its
  subclasses
• Do NOT automatically trigger a rollback by the
  container
• A rollback can be initiated in code
  (setRollbackOnly -- ex. charging customer)

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Exceptions -- System Exceptions

• Any RuntimeException(s)
• java.rmi.RemoteException or its subclasses
• DO automatically trigger a rollback by the
  container
• Exceptions logged by container
• EJB instance is discarded
• May be more or less transparent to the user
• Depends on state (or lack thereof) of the bean
• Depends on vendor provisions (i.e. BES stubs make
  things VERY transparent in a clustered
  environment)

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Exceptions -- RentalManager EJB

• Application Exception -- rollback only set,
  exception rethrown
• SQLException (System) converted to EJBException
  and thrown

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EJB 2.1 / 3.0
Coming Soon to a Container Near You!
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Whats New in EJB 2.1

• Better web services support
• web services endpoints for SLSBs -- easy access
  for external clients
• EJBs can tap into external web services more
  easily
• ex. .NET and J2EE interoperability
• Container-managed timer service via
  javax.ejb.TimedObject interface and the
  ejbTimeout method
• Polling for events to trigger business logic
• CRON or Autosys job replacement potential

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Whats New in EJB 2.1

• EJB QL enhancements
• ORDER BY (ascending or descending)
• AVG, MAX, MIN, SUM, COUNT, MOD
• The door has been opened for MDBs to use
  messaging protocols other than JMS (i.e. JAXM)

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Whats New in EJB 3.0

• http//www.jcp.org/en/jsr/detail?id220
• Its all about the beans, baby!
• Bye, bye interfaces
• Hello annotations
• Example
• _at_Session public class MyEJBThreeOBean
• public void youCanDoIt(boolean really) ...
  

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Whats New in EJB 3.0

• http//www.martinfowler.com/articles/injection.htm
  l
• Dependency Injection vs. JNDI lookups
• Example
• _at_Session public class MyEJBThreeOBean
• private DataSource myDS
• _at_Inject private void setMyDS(DataSource
  theDS)
• myDS theDS
• public void methodCallingMyDAO()
• ...
• Connection c myDS.getConnection()
• ...

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If theres time...

• Deployment Issues (JARs, EARs, etc.)
• JUnit w/ EJBs
• Debugging Example
• Profiling Example

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Questions?
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Thank You

• 3036
• Enterprise Java Beans
• Please fill out the speaker evaluation
• You can contact me further at pmcmichael_at_pillart
  echnology.com