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Overview of Enterprise JavaBeans EJB

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Enterprise. Java. What didn't we address ? Could ... Enterprise Java Beans (EJB) CORBA Components ... enterprise resources at the third tier (Databases) ... – PowerPoint PPT presentation

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Title: Overview of Enterprise JavaBeans EJB


1
Overview of Enterprise JavaBeans (EJB)
  • Source
  • Enterprise JavaBeans, Richard Monson-Haefel

2
Applications to Date
  • 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

3
What didnt we address ?
  • Could someone else deploy your application?
  • Component reusability
  • Security
  • Threading
  • Resource Management
  • Load-Balancing
  • Fault Tolerance (a little with activation)

4
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

5
Components Vs. Objects
  • Usually larger-grained
  • Provide a complete capability
  • Credit Card Verification
  • Can be customized for deployment

6
Component Architectures
  • Client-Side
  • Applets
  • Java Beans (development components)
  • ActiveX
  • Server Side
  • Servlets
  • Enterprise Java Beans (EJB)
  • CORBA Components
  • Microsoft Distributed interNet Applications
    Architecture (DNA)

7
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

8
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.

9
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 isnt 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

10
Enterprise JavaBeans (EJBs)
  • Standard server-side component model for Java
    Enterprise Applications
  • security
  • resource pooling
  • persistence
  • concurrency
  • transactional integrity
  • 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

11
EJBs (cont.)
  • Java
  • 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
  • IBMs Websphere
  • BEAs Weblogic Server and Weblogic Enterprise
  • Gemstone/J
  • ...

12
EJB Architecture
  • Interfaces and Classes
  • beans
  • entity bean
  • session session
  • Stateless session bean
  • Statefull session bean
  • primary key
  • home interface
  • remote interface (EJB Object)
  • Container
  • Application Server

13
EJB Conceptual Class Overview
14
Bean Class Instance Lifecycle
No State
1 newInstance() 2 setEJBContext()
Pooled State
3 bean associated to an EJB Object
5 bean disassociated from EJB Object
Ready State
4 service client requests
15
Bean Types
  • Entity 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 (statefull
    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

16
Bean Usages
  • Entity 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

17
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

18
EJB Classes and Interfaces
19
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
  • clients 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

20
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

21
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

22
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

23
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

24
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

25
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
    C CORBA TIE class

26
Bean Class (cont.)
  • Clients never interact with bean classes
    themselves
  • always interact with the bean through home
    (create, find, remove) and remote 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

27
Bean Class (cont.)
  • implements javax.ejb.EntitySessionBean
  • extends empty javax.ejb.EnterpriseBean extends
    java.io.Serializable
  • set/unsetEntity/SessionContext()
  • 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
    objects state

28
Bean Class (cont.)
  • ejbPassivate()
  • container calls this method when the instance is
    being dis-associated with a particular EJB Object
    (pre serialization)
  • ejbActivate()
  • container calls this method when the instance is
    taken fro a pool of available instances and
    associated with a particular EJB Object (post
    de-serialization)
  • ejbRemove()
  • container calls this method of an instance before
    removing an EJB Object from the system

29
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), completion event
    (container managed)

30
Bean Class Example CabinBean
  • package com.titan.cabin
  • import javax.ejb.EntityContext
  • public class CabinBean implements
    javax.ejb.EntityBean
  • public int id
  • public String name
  • public int deckLevel
  • public int ship
  • public int bedCount

31
Bean Class Example CabinBean (cont.)
  • public void ejbCreate(int id)
  • this.id id
  • public void ejbPostCreate(int id)
  • // Do nothing. Required.
  • public String getName()
  • return name
  • public void setName(String str)
  • name str
  • public int getShip()
  • return ship

32
Bean Class Example CabinBean (cont.)
  • public void setShip(int sp)
  • ship sp
  • public int getBedCount()
  • return bedCount
  • public void setBedCount(int bc)
  • bedCount bc
  • public int getDeckLevel()
  • return deckLevel

33
Bean Class Example CabinBean (cont.)
  • public void setDeckLevel(int level )
  • deckLevel level
  • public void setEntityContext(EntityContext
    ctx)
  • // Not implemented.
  • public void unsetEntityContext()
  • // Not implemented.
  • public void ejbActivate()
  • // Not implemented.
  • public void ejbPassivate()
  • // Not implemented.

34
Bean Class Example CabinBean (cont.)
  • public void ejbLoad()
  • // Not implemented.
  • public void ejbStore()
  • // Not implemented.
  • public void ejbRemove()
  • // Not implemented.

35
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 beans
    primary key value(s).

36
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)

37
Containers
  • Manages interaction between the bean and its
    server
  • Provides a uniform interface to the bean and to
    the server

38
Containers (cont.)
  • Creates new instances of beans and manages their
    persistence
  • provides mapping between bean and containers
    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

39
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

40
Deployment Descriptor Example ejb-jar.xml (Cabin)
  • Inc.//DTD Enterprise JavaBeans 1.1//EN"
    "http//java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd"
  • This Cabin enterprise bean
    entity represents a cabin on a cruise
    ship.
  • CabinBean
  • com.titan.cabin.CabinHome
  • com.titan.cabin.Cabin
  • com.titan.cabin.CabinBean-class

41
Deployment Descriptor Example (cont.)
  • Containertype
  • com.titan.cabin.CabinPKprim-key-class
  • False
  • id
  • - name
  • - deckLevelname
  • - ship
  • - bedCountame
  • ...

42
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

43
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

44
Example Client
  • Context jndiContext getInitialContext()
  • Object obj jndiContext.lookup("ejb/CabinHome")
  • System.out.println("found it! " obj)
  • CabinHome home (CabinHome)javax.rmi.PortableRemo
    teObject.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)

45
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())

46
Usage Scenarios
47
Creating an Account Object
AccountBean
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
48
Accessing an Account Object
AccountBean
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)
49
Deleting an Account Object
AccountBean
AccountBean
3 select instance 10 return instance
AccountBean
2 select 7 delete
bean pool
4 populate state 5 ejbLoad() 6 ejbRemove()
1 remove(pKey)
AccountHome_EJBHome
8 remove()
Client
Account_EJBObject
AccountBean
50
Questions to Ponder...
  • Entity bean, stateful session bean, stateless
    session bean?
  • object which requires access by multiple clients
    over its lifetime
  • object whose work accepts and returns all
    information in the call
  • 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 11 between instanced
    of beans (EJB Objects) and instances of the bean
    class?
  • What GoF Pattern does this depict?
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