Enterprise JavaBeans v2'0

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Enterprise JavaBeans v2.0

• Overview of changes in the Enterprise JavaBeans
  Specification
• Presented by Douglas WF Acheson
• bea Canada Professional Services
• July 25th, 2001

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Agenda

• Changes in the EJB Specification
• New home methods
• Local versus Remote Interfaces
• New Hope for Container Managed Persistence
• Container Managed Persistence Example
• JMS Review
• Message-Driven Bean (MD Beans) JMS and EJBs a
  New Relationship
• MD Bean Example

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Brief History

• Suns entrance into the distributed component
  arena was through EJBs
• v1.0 of EJB specification March 1998
• v1.1 of EJB specification December 1999
• v2.0 Proposed Final Draft late June 2001
• Note this is only a draft of the final proposal
• Changes may occur before the final publication

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Changes in the EBJ Specification

• Some of the significant changes in the
  specification, to date, are
• Home Methods
• Local and Remote Interfaces
• An improved architecture for CMP including a
  query language
• Message-Driven Beans

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Home Methods for EJBs

• New in v2.0 specification is the concept of Home
  methods
• Provides an easy way to perform business logic
  that does not require actual instance of an EJB
• Very few restrictions for home methods
• Each method must throw java.rmi.RemoteException
• Signature must not resemble a finder method or
  instance method
• Can perform any business logic that does not
  involve the EJB instance

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Local versus Remote Interfaces

• The remote interface is the same concept as from
  previous specifications
• Remote objects utilize Pass-By-Value
• Location independent
• Relies on Java RMI APIs
• The local interface are new to v2.0 specification
• Objects are co-located in the same JVM location
  dependent
• Local objects utilize pass-by-reference
  (increases performance)
• Tighter coupling between objects
• Light-weight access to components

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Local versus Remote InterfacesContinued

• Example of using a local interface
• A user requests services from EJB 1 which in turn
  require services from EJB 2

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New Hope for Container Managed Persistence

• Container Managed Persistence (CMP) allows the
  bean developer to concentrate more on business
  logic design and development
• The bean developer is still responsible for
  defining the mapping between the bean properties
  and the persistent fields of the database
  (achieved through the deployment descriptor)
• v2.0 of the specification does not solve complex
  O-R mapping requirements, but does allow for
  advanced object representation of relational
  stores
• WebLogic Server supports this through the use of
  a Persistence Manager, which is part the the
  container

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New Hope for Container Managed Persistence
Continued

• v2.0 of the specification removes the concept of
  publicly accessible attributes and replaces them
  with accessor methods
• All accessor methods are declared by the bean
  developer, not implemented by the bean developer
• Each of the accessor methods are declared
  abstract
• In addition, the bean is declared abstract
• The bean developer does not defined the bean
  properties, only the accessor methods
• For each bean attribute/property there is a
  corresponding declaration in the deployment
  descriptor

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New Hope for Container Managed Persistence
Continued

• Each field (property) of the bean must be
  declared as persistent field (CMP) or relational
  field (CMR)
• Container Managed Persistence CMP
• The ordinary single unit of data
• Example age
• Container Managed Relationship CMR
• An aggregate collection of data (reference to
  another EJB or dependent entity object)
• Example address

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New Hope for Container Managed Persistence
Continued

• Persisted fields are described in the ejb-jar.xml
  file
• Persisted fields are mapped to database columns
  in the weblogic-cmp-rdbms-jar.xml file
• Query logic for finder methods are located in the
  ejb-jar.xml file

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EJB Query Language

• New to the v2.0 specification is the introduction
  of the EJB Query Language (EJB QL)
• EJB QL defines query methods for finder and
  select methods used by CMP entity beans
• It is intended to be portable across EJB
  containers
• Based on SQL92, however, it has been enhanced to
  allow querying or navigation over entity bean
  relationships
• EJB QL works with objects whereas SQL works with
  tables
• Application provider must do translation between
  EJB QL and SQL
• EJB QL has some built in functions not as many as
  SQL

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EJB Query Language Continued

• EBJ QL contains functions that do not have
  equivalent methods in SQL
• substring
• concat
• There exists functions in EJB QL with the same
  name in SQL, yet have different meanings
• Outlined in the specification is the suggestion
  that the transformation from EJB QL to SQL be
  application vendors persistence manager
• For complete list see the specification found on
  the JavaSoft web site

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WLS Entity EJB Enhancements

• Weblogic enhances the new Container Managed
  Entity Beans with new deployment descriptor
  directives
• Able to load an entire EJB (graph) or part of the
  graph with a single query
• This loading can be accomplished immediately via
  the finder methods or lazily on demand via
  accessor methods
• The ltfield-groupgt tag allows data to be loaded
  together when any of the data is accessed
• Read-mostly pattern now officially part of WLS
  v6.1
• CMP beans need to be configured with a connection
  pool with gt 1 connections
• WebLogic Server's CMP service may need to get two
  connections simultaneously

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WLS Entity EJB Enhancements Continued

• What is the Read-mostly pattern used by WLS
• Under this pattern two versions of the same EJB
  are deployed
• A read/write/transaction bean
• A read-only/non-transactional bean
• Any transaction is committed through a read/write
  cache
• Once completed a multicast message is sent out to
  all read-only caches to invalidate the data
• This allows synchronization of read/write and
  read caches

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Container Managed Persistence Example

• This example shows a dependant object
  relationship (1-1)

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Container Managed Persistence Example Continued

• Source Code for Customer Remote Interface
• public interface Customer extends EJBObject
• public String getName() throws RemoteException
  
• public boolean isRegular() throws
  RemoteException
• public boolean isPremium() throws
  RemoteException
• public boolean isVIP() throws RemoteException
• public Account getAccount() throws
  RemoteException
• public void setAccount(Account a)
• throws RemoteException

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Container Managed Persistence Example Continued

• In the ejbCreate set the non-dependent objects
• In the ebjPostCreate set the dependent objects
• public void ejbPostCreate(String name, int level)
  throws CreateException
• setAccount(null)

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Container Managed Persistence Example Continued

• Accessor Methods used to define the bean
  attributes
• public abstract String getName()
• public abstract void setName(String name)
• public abstract Account getAccount()
• public abstract void setAccount(Account a)
• public abstract int getLevelOfImportance()
• public abstract void setLevelOfImportance(int
  val)

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Container Managed Persistence Example Continued

• ejb-jar.xml excepts
• ltentitygt
• ltejb-namegtCustomerEJBlt/ejb-namegt
• ltpersistence-typegtContainerlt/persistence-typegt
• ltreentrantgtFalselt/reentrantgt
• ltcmp-versiongt2.xlt/cmp-versiongt
• ltabstract-schema-namegtCustomerEBean
• lt/abstract-schema-namegt
• ltcmp-fieldgtltfield-namegtnamelt/field-namegt
• lt/cmp-fieldgt
• ltprimkey-fieldgtnamelt/primkey-fieldgt

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Container Managed Persistence Example Continued

• ejb-jar.xml excepts Continued
• ltquerygt
• ltquery-methodgt
• ltmethod-namegtfindByImportancelt/method-namegt
• ltmethod-paramsgt
• ltmethod-paramgtintlt/method-paramgt
• lt/method-paramsgt
• lt/query-methodgt
• ltejb-qlgt
• lt!CDATAFROM CustomerEBean c WHERE
• c.levelOfImportance gt ?1gt
• lt/ejb-qlgt
• lt/querygt
• lt/entitygt

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JMS Quick Review

• November 1999 Sun release v1.0.2 of Java
  Messaging Service (JMS) specification
• JMS is a set of interfaces and associated
  semantics that define how a JMS client accesses
  the facilities of an enterprise messaging product
• JMS does not define how the JMS vender should
  implement the messaging system
• BEA Weblogic Server, all version, provide JMS
  services as described by the JMS specifications

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JMS Quick Review Continued

• JMS supports both pub-sub (topic) and
  peer-to-peer (queue) message deliver mechanisms
• JMS operations can be transaction ware

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Message-Driven Beans

• v2.0 of the specification introduces a new type
  of Enterprise JavaBeans Message-Driven Bean
  (MDBean)
• Introduced to handle the processing of
  asynchronous requests
• Theses beans are stateless and transaction-aware
• MDBeans are consumers of JMS messages
• The MD Beans have no home, remote, or local
  interfaces
• All interaction is via the JMS through the
  container
• Clients cannot invoke a MD Bean without a JMS
  message

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Message-Driven Beans Continued

• Benefits of Message-Driven Beans
• Not bound to a JMS Queue or Topic like regular
  JMS consumers
• Dynamic JMS binding via deployment descriptor
• Inherits benefits of Enterprise Java Beans
• Transaction Control
• Memory Management
• Security Integration
• Drawbacks for Message-Driven Beans
• Unable to listen on multiple JMS channels as
  regular JMS consumers are able

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Message-Driven Beans Continued

• To create a Message Driven Bean there are two
  interfaces that must be implemented
• javax.ejb.MessageDrivenBean
• javax.jms.messageListener
• The javax.ejb.MessageDrivenBean has three methods
• ejbCreate()
• ejbRemove()
• setMessageDrivenBeanContext(MessageDrivenBeanConte
  xt)
• The javax.jms.messageListener
• onMessage(Message)

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Message-Driven Beans Continued
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Message-Driven Beans Continued
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Message-Driven Beans Example

• An example of a Message-Driven Bean would be
  distributed logging

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Message-Driven Beans Example Continued

• Source Code
• Public class Logger implements MessageDrivenBean,
• MessageListener
• private MessageDrivenContext ctx null
• public void Logger()
• public void ejbCreate()

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Message-Driven Beans Example Continued

• public void ejbRemove()
• public void setMessageDrivenContext
• (MessageDrivenContext
  ctx)
• this.ctx ctx
• public void onMessage(Message message)
• // place logging code here

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Message-Driven Beans Example Continued

• ejb-jar file
• ltejb-jargt
• ltenterprise-beansgt
• ltmessage-drivengt
• ltejb-namegtLoggerlt/ejb-namegt
• ltejb-classgtcom.bea.ug.Loggerlt/ejb-classgt
• lttransactiongtcontainerlt/transactiongt
• ltjms-acknowledge-modegt
• auto-acknowledge
• ltjms-acknowledge-modegt

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Message-Driven Beans Example Continued

• ejb-jar file continued
• ltmessage-driven-destinationgt
• ltjms-destination-typegt
• javax.jms.Topic
• lt jms-destination-typegt
• lt/message-driven-destinationgt
• lt/message-drivengt
• lt/enterprise-beansgt
• lt/ejb-jargt

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Message-Driven Beans Example Continued

• weblogic-ejb-jar file
• ltweblogic-ejb-jargt
• ltweblogic-enterprise-beangt
• ltejb-namegtLoggerlt/ebj-namegt
• ltmessage-driven-descriptorgt
• ltmax-beans-in-free-poolgt10ltmax-beans-in-free
  -poolgt
• ltintital-beans-in-free-poolgt10
• ltinitial-beans-in-free
  -poolgt
• ltdestination-jndi-namegtLoggerQueue
• ltdestination-jndi-name
  gt
• lt/message-driven-descriptorgt
• lt/weblogic-enterprise-beangt
• lt/weblogic-ejb-jargt

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Resources

• http//developer.java.sun.com/developer/technicalA
  rticles/ebeans/ejb20/index.html
• http//www.javasoft.com/products/ejb/docs.html
• http//www.theserverside.com/resources/index.jsp
• http//edocs.bea.com

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Questions and Answers
?