Enterprise JavaBeans Overview

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Enterprise JavaBeans Overview

• Presented by
• Eric Gudgion

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What are EJBs

• Enterprise JavaBeans are a server side standards
  based component model.
• Provides a frame work for methods, naming,
  transactions, security, persistence, life-cycle.
• Concentrate on business logic.
• Scalable architecture.

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Why Business Components?

• Separate Business Logic from Plumbing and Glue
• Separate Component Development from Assembly and
  Deployment
• Manage Software as Depreciable Business Assets
• Offer easy integration with business components
  and enterprise data
• Enable portability across platforms

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What are Enterprise JavaBeans (EJB)?
An EJB defines a component model for developing
and deploying Server-Side business objects.

• CHARACTERISTICS
• A Server-Side business Component
• Written in 100 Java
• Distributed over a network
• Always called by a Client
• Transactional
• Secure
• Two Types (Entity and Session)

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The Right Bean For the Job
DBMS

• Enterprise JavaBeans
• Distributed Components for assembling networked
  applications
• Server-side
• No GUI
• Core features methods, naming, transactions,
  security, persistence, life-cycle
• Separates business logic container

• JavaBeans
• Components for assembling local application
• Generally client-side
• Often GUI-oriented
• Core features methods, properties, events,
  introspection, customization
• Separates design runtime environments

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Architecture
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Technical View of an EJB Session(Analogy
Collect Phone Call)
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Session and Entity Beans
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Client side
// lookup home from JNDI AccountHome home
(AccountHome) jndiCtx.lookup("bank.accounts")
Account myAccount home.create(...) Account
momsAccount home.findByPrimaryKey() tx.begin
() momsAccount.withdraw(5000) myAccount.deposit(
5000) tx.commit()
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State Management Persistence
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Compare the 2 Types of EJBs
Session EJB
Entity EJB

• Analogous to a Shopping Cart
• Represents one User connection
• Can be Stateless (ex. simple query) or Stateful
  (more typical for shopping cart)
• Exists for life of Session only
• Not Persistent destroyed if server crashes
• Contains Business Logic
• May or may not be Transactional

• Analogous to an Item in the Cart
• Represents one row in a database
• Purely Stateful (represents the data)
• Exists beyond the Session
• Persistent
• Contains Business Logic
• May or may not be Transactional

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EJB Taxonomy
Enterprise JavaBeans
Entity Beans Component view of DB row or
object May be long-lived Primary key,
stateful 1-to-many relationship to
client(s) E.g., Customer, Order

• Session Beans
• TPM/OTM style
• Short-lived, no key
• 1-to-1 relationship to client
• Explicit DB access
• E.g., Bank Teller, E-Commerce
  Server

Many EJB applications will use both!
Entity Beans
Session Beans
(via explicit JDBC when automated tools are
insufficient)
(Web shopping cart)
(Inventory agent)
(via O/R mapping)
Stateful
Stateless
Bean- Managed
Container- Managed
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Persistence

• Container (typically) handles object persistence
  automatically.
• Bean written is backing store independent.
• Containers for SQL DBMS, OODBMS, ORDBMS, file
  system, directory service.
• Deployment Descriptor properties hold
  container-specific persistence properties, like
  attribute-column mappings.

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Bean References
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Persistence DD Wizard Pane
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Persistence Deployment Descriptor

• (persistentStoreProperties
• persistentStoreType jdbc
• (jdbc
• tableName ejbAccounts
• dbIsShared false
• poolName ejbPool
• driverName weblogic.jdbc.jts.Driver
• (attributeMap
• EJBean attribute Database column
  name
• -------------------------------------
  ----
• accountId id
• balance bal
• ) end attributeMap
• ) end jdbc
• )

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Transactions
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Transactional Definition (ACID)

• Atomic, transactions are all or nothing, never
  incomplete.
• Consistent, always leave the system in a
  consistent state.
• Isolated, execute in a safe manner, without
  effecting each other.
• Durable, once completed and committed, survive a
  system failure.

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Transaction Management

• Uses Java Transaction Service (JTS).
• EJB Server handles TX ID propagation.
• Declarative TX management through Deployment
  Descriptor
• Per-method and Bean-wide scope.
• EJB Container performs TX begin, commit, and
  rollback, and provides 2PC semantics on beans
  behalf.

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Transaction Control Descriptors

• TX_NOT_SUPPORTED - Bean does not have
  transactions
• any active transactions are suspended during
  method call.
• TX_REQUIRED - Transaction scope required, one is
  created if the scope does not exist.
• TX_SUPPORTS - If the client has transaction scope
  the bean will use it, otherwise no scope is used.
• TX_REQUIRES_NEW - Container creates new
  transaction.
• TX_MANDATORY - Transaction scope always required.
• TX_BEAN_MANAGED - Bean will manage its scope.

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Isolation Level Description

• TRANSACTION_READ_UNCOMMITTED - Can read
  uncommitted data.
• TRANSACTION_READ_COMMITTED - Cant read
  uncommitted data.
• TRANSACTION_REPEATABLE_READ - Cant change data
  thats being read by another transaction.
• TRANSACTION_SERIALIZABLE - Transaction has
  exclusive read and update privileges.

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Transaction DD Wizard Pane
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Transaction DD

• (controlDescriptors
• (DEFAULT
• isolationLevel TRANSACTION_SERIALIZABLE
• transactionAttribute TX_MANDITORY
• )
• (buy
• isolationLevel TRANSACTION_SERIALIZABLE
• transactionAttribute TX_REQUIRED
• ) end buy
• ) end controlDescriptors

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Security
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EJB Security Management

• EJB Server propagates security context.
• Declarative security attributes in DD.
• Access control per-method and bean-wide
• SetUID functionality RunAsMode and
  RunAsIdentity
• Container enforces access control and sets beans
  identity as described in DD

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WebLogic Real-World Security

• SSL protocol
• RSA Encryption
• X.509 Digital certificates
• Access Control List functionality
• Integrated with leading Internet security vendors

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Access Control DD Wizard Pane
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Deployment
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EJB Packaging

• EJB Jar file contains
• Deployment Descriptor (Serializable Entity or
  Session Java Class)
• Beans Home Remote Interfaces
• Beans Home Class Names
• Beans Implementation Code
• Environmental Properties
• Access Control Lists
• Transaction Control Descriptors
• Manifest File (Declares Descriptor as Bean)
• All Handled by Server Vendor!

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Deployment Descriptor
(EntityDescriptor beanHomeName
bank.accounts enterpriseBeanClassName
AccountBean homeInterfaceClassName
AccountHome remoteInterfaceClassName Account
)
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Summary
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Development Deployment Roles

• EJB provider (domain expert) writes bean
• Application assembler combines beans into a
  system
• Deployer knows a specific EJB environment
  (server container) BEA WebLogic
• EJB Server provider BEA WebLogic
• EJB Container provider BEA WebLogic partners
• System Administrator runs the EJB Server

Vendor-independent role
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EJB Benefits

• Concentrate on business logic.
• Higher-level semantics security, transactions,
  persistence, naming.
• Component System-Independent Components.
• Component roles bean writer, deployer,
  server,container.
• Scalable architecture.

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Helpful Tools

• StructureBuilder - www.webgain.com
• Rational Rose - www.rational.com
• Introscope - www.wilytech.com
• Visual Café - www.webgain.com
• Visual Age - www-4.ibm.com/software/ad/vjava

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Useful Books

• Title Enterprise JavaBeans
• Publisher OReilly ISBN 1-556592-605-6
• Author Richard Monson-Haefel
• Title Java Enterprise in a Nutshell
• Publisher OReilly ISBN 1-56592-483-5
• Author David Flanagan, Jim Farley, William
  Crawford Kirs Magnusson
• Title Mastering Enterprise JavaBeans and the
  Java 2 Platform Enterprise Edition
• Publisher Wiley ISBN 0-471-33229-1
• Author Ed Roman

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Internet Resources

• http//www.bea.com
• http//java.sun.com/products/ejb
• http//www.ejbnow.com
• http//www.jguru.com
• http//www.javadevelopersjournal.com
• news//www4.weblogic.com/weblogic.developer.intere
  st.ejb