J2EE Introduction

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J2EE Introduction

• EJB, JSP/Servlets, JMS, JDBC

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TerminologyJ2EE

• A specification
• Version 1.4 document (24 Nov 2003, 246 pgs.)
• Response to JSR-151 (not just a Sun thing)
• Umbrella which freezes other technologies
• Each has its own spec / rev reference
  implementation
• A Download
• Interfaces (javax. above / beyond J2SE)
• Reference implementation
• Rollup of individual technologies reference
  implementations
• E.g. Tomcat 4.X for Servlet 2.0
• Compatibility Test Suite
• BluePrints (best practices documents)

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J2EE Goals

• High Availability
• Security
• Reliability
• Scalability
• of Enterprise Information Services (EISs),
• Usually in a multitier environment.

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J2EE Technologies Givens

• J2SE 1.4.2_02
• JDBC 3.0 java.sql
• javax.sql
• JAXP 1.2 org.w3c.dom
• org.w3c.sax (3)
• javax.xml.parsers
• javax.xml.transform (4)
• JTA 1.0 javax.transaction.xa
• JNDI javax.naming (DNS, LDAP, COS, RMI)
• RMI-IIOP javax.rmi
• org.omg. (30)
• JavaIDL, CORBA

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J2EE Technologies Top Four

• EJB 2.1 javax.ejb
• Servlet 2.4 javax.servlet
• JSP 2.0 javax.servlet.jsp (3)
• JMS 1.1 javax.jms

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J2EE Technologies 11 More

• JavaMail 1.3 javax.mail
• JAF 1.0 javax.activation
• Connector 1.5
• Web Services 1.1 javax.xml.
• JAX-RPC 1.1
• SAAJ 1.2
• JAXR 1.0 javax.resource.
• J2EE Mgmt 1.0 javax.management.
• JMX 1.2
• J2EE Deploy 1.1 javax.enterprise.deploy.
• JACC 1.0 javax.security.jacc

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Application Component Types

• Applets (Just like conventional Applet)
• Application Clients
• Just like conventional J2SE application
• Except may require J2EE APIs
• JSP / Servlet
• Anything that talks HTTP
• Requires container Apache/Tomcat is RefImpl
• EJB
• Transactional component
• Requires container server
• Download gives you RefImpl

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TerminologyEJB

• A specification from Sun Microsystems
• EJB 1.1 document (285 pgs.)
• javax.ejb. interfaces (12)
• NOT an implementation! NOT JavaBeans!
• Framework for enterprise components
• Alternatives DCOM, CORBA
• 50,000 ft view
• J2EE, J2SE, J2ME (EJB part of J2EE)
• Related J2EE specs JNDI, JMS, JTA, JAAS

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EJB Spec...Six Roles

• The CastIn Order of Appearance
• 1. EJB Server Provider
• 2. EJB Container Provider
• 3. EnterpriseBean Provider
• 4. Deployer
• 5. Application EJB Client Assembler
• 6. System Administrator
• EJB Spec lists roles in a different order
• EnterpriseBean-centric vice chronological

Combined for our purposes...
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EJB Server Container

• Implement majority (4/5?) of EJB spec
• Provide backbone of EJB System
• Mediator among other players
• EJB Clients
• EnterpriseBeans
• At least one backend database
• Various implementations (cross compatible)
• BEA/Weblogic, IBM/Websphere, 8 others
• EJB 2.X should clear up Container bounds

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Terminology...EnterpriseBean1

• Reusable software component
• Logic only no GUI
• Built / bought to meet a business need
• Banking BankAccountBean
• Shipbuilding ProductStructureBean
• Deployed to an EJB Server implementation
• Serves multiple users across enterprise
• HR, Finance, Design, Planning, Ops, Logistics

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Terminology...EnterpriseBean2

• Compiled Java class file
• Implements EnterpriseBean interface
• Instantiated (newd) by Container
• Satisfies client needs for objects of type X
• Maps to two java.rmi.Remote interfaces
• XHome (home, used by client to create / find)
• X (used by client to execute business methods)
• Doesnt actually implement X and XHome
• EJB Compiler (from Container) enforces mapping

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TerminologyEJB Client

• Application that uses EnterpriseBeans
• GUI or non-GUI (e.g. Servlets)
• Java or CORBA
• Remote or local (EB Intranet NNS other
  EnterpriseBeans)
• Client view is remote interfaces
• XHome Xbut NOT EnterpriseBean!
• Considered less trustworthy than server side
• Client flaw should not affect EJB Server

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EJB Architecture
EJB Server
Container
XHome
create() find()
EnterpriseBean
Client
X
Existing Database
(Wire)
(Wire)
Tier 1Tier 2..Tier N
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Why All the Fuss?

• The Alternative a straight RMI impl
• XImpl provides not only business logic, but also
• transactions, security, concurrency, access
  control, database connectivity
• EJB separates responsibilities
• Business logic goes in the EnterpriseBean
• systems stuff is provided by Server / Container

X
Client
XImpl
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Relationship to UML

• Each UML class is an X
• EB writes X, XHome remote interfaces
• Specify client-side contract
• Ensure cross-project needs are met
• CSC implements EnterpriseBean for X
• Satisfy X, Xhome
• Map to persistent store
• Arbitrate where business logic resides
• No code generation (today)

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EJBean Lifecycle
Doesnt Exist
ejbFind()
pooled
ejbPassivate()
ejbRemove()
ejbCreate()
ejbActivate()
ready
ejbLoad()
ejbStore()
businessMethod()
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Outline for Lesson 2

• Intro to javax.ejb package
• Writing Java Code
• How to write an EntityBean
• Bean-managed Persistence (BMP)
• Container-managed Persistence (CMP)
• How to write a SessionBean
• Writing a Deployment Descriptor
• Manifests, ejb-jars, and EJB Compilers
• Deploying an EnterpriseBean

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Terminology...EntityBean

• EnterpriseBean that is long lived
• Maps to backend data store
• Bean-managed persistence
• Container-managed persistence
• Has unique key (primary key or XPK)
• Implements EntityBean interface
• Examples
• EmployeeBean with SSN as PK

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TerminlogySessionBean

• EnterpriseBean that is short lived
• Duration no longer than user login
• State not stored to any database
• Examples
• ShoppingCartBean
• TableModelBean
• Implements EnterpriseBean interface

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javax.ejb Package

• 6 classes
• All are of type Exception
• Cover this in greater detail in Lesson 3
• 12 interfaces
• 6 are seen by EJB Client
• other 6 are only seen by EJB Server/Container
• Often implement java.io.Serializable or
  java.io.Remote
• Thats it.

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javax.ejb Interfaces (5/12)
java.rmi.Remote
java.io.Serializable
javax.ejb.EnterpriseBean
javax.ejb.EJBHome
javax.ejb.EJBObject
javax.ejb.SessionBean
javax.ejb.EntityBean
YBeanImpl
X
XHome
YHome
Y
XBeanImpl
Client Server
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Reality Check

• What does the Bean Provider provide?
• Which are concrete? Which are interfaces?
• EB Roles? CSC/AD Roles?
• Why have X, Y interfaces without impls?
• What can we say about reqd methods on
• X, Y?
• Xhome, Yhome?
• XBeanImpl?
• YBeanImpl?

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X,Y Required Methods

• Entity, Session bean remote interfaces share
  EJBObject
• EJBHome getEJBHome()
• Handle getHandle()
• Object getPrimaryKey()
• boolean isIdentical(EJBObject obj)
• Similar to .equals() method
• void remove()
• EJBObject extends java.rmi.Remote

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XHome,YHome Reqd Methods

• Entity / Session share EJBHome interface
• Summation of Requirements
• EJBMetaData getEJBMetaData()
• void remove(Handle handle)
• void remove(Object primaryKey)
• void create() // Session/Entity
• void findXXX() // Entity Only
• Any EJBean can be referenced either by handle or
  primaryKey. EJBHome provides means for removing.
  
• All create()s must be named create, but may be
  overloaded
• All findXXX()s map to ejbFindXXX on EJBean.

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XBeanImpl Required Methods

• Entity beans are distinct from Session
• But no distinction between Bean Managed
  Container Managed Persistence
• Void ejbActivate()
• Invoked by container to associate with EJBObject
• void ejbLoad()
• Do a database lookup (bean-managed persistence
  only)
• void ejbPassivate()
• Invoked by container about to get dissociated
  with EJBObject
• void ejbRemove()
• void ejbStore()
• - Persist yourself to database (bean-managed
  persistence only)
• void setEntityContext(EntityContext ctx)
• void unsetEntityContext()

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YBeanImpl Required Methods

• SessionBeans are distinct from Entity

Void ejbActivate() void ejbPassivate() void
ejbRemove() void setSessionContext(SessionContext
)
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Division of EffortEntityBean

• Decide on UML model
• EB
• Write XHome and X interfaces
• EB
• Write XBeanImpl
• CSC

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Client Side...Handle

• EJBObject getEJBObject()
• Any handle has knowledge of home as well as key,
  so it can be used to locate and return reference
  to EJBObject.
• All handles are Serializable

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Client Side...EJBMetaData

• EJBHome getEJBHome()
• Class getHomeInterfaceClass()
• Class getPrimaryKeyClass()
• Class getRemoteInterfaceClass()
• boolean isSession()
• Allow introspection by remote integrated
  development environments.

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Server SideEnterpriseBean

• Common superclass of
• SessionBean
• EntityBean
• extends Serializable
• Thats it!

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Server SideEJBContext

• Identity getCallerIdentity()
• Identify caller on per-call basis
• EJBHome getEJBHome()
• Properties getEnvironment()
• boolean getRollbackOnly()
• dont waste time if rollback set
• UserTransaction getUserTransaction()
• boolean isCallerInRole(Identity role)
• implement role-based access
• void setRollbackOnly()
• set rollback so other trans dont waste time