Enterprise JavaBeans 3'0 to be released in 2006

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Enterprise JavaBeans 3.0to be released in 2006

• Jacek Ratzinger
• Distributed Systems Group
• Vienna University of Technology

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Outline

• Rational for Change
• Concepts
• Annotations
• Dependency Injection
• EJB types and their specifics
• EJB-QL
• standardize Hibernate?
• Client Programming Model
• Pros and Cons

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Rational for Change

• EJB 2.x has become overly complex
• to many artifacts for developers
• to many interfaces in EJB 2.x (home, ejb)
• unnecessary exceptions, callback methods
• no standard way to define a primary key
• EJB 3.0 makes another attempt promise reducing
  EJB's complexity for developers
• simpler domain models with Plain Old Java Objects
  (POJOs)

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Drive for EJB 3.0

• decrease number of artefacts
• home interfaces and deployment descriptors
• program annotations introduced in Java 5
• light-weight domain modelling
• including inheritance and polymorphism
• configuration by exception
• dependency injection
• reduction of checked exceptions
• testing outside the container

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Java 5.0 Annotations

• annotations do not directly affect program
  semantics
• can be inspected through source parsing or by
  using the additional reflection APIs
• define custom annotations
• annotate fields, methods, classes, etc.
• used to define
• bean's business interface
• O/R mapping information (specific persistence)
• resource references
• deployment information

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Dependency Injection

• beans may gain references to resources by having
  the container supply it with those
• bean instance variables or setter methods are
  annotated as targets
• standard way annotations
• alternatively, lookup method of
  javax.ejb.EJBContext or the JNDI APIs
• container responsibility before use

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Dependency Injection

• annotation of instance variables
• _at_Resource(name"myDB") //type inferred
• public DataSource customerDB
• setter injection
• public DataSource customerDB
• _at_Resource(name myDB)
• public void setDataSource(DataSource myDB
• this. customerDB myDB

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Specifics of EJB 3.0

• Exceptions
• interface may declare arbitrary exceptions
• should not throw java.rmi.RemoteException
• EJBException thrown by the container
• Callbacks and Callback Listener Classes
• no callbacks (e.g. ejbCreate(), ejbPassivate) for
  life cycle events required
• method annotations for callbacks
• callback listener class may be used instead of
  callback methods

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Entity Beans

• POJOs with annotation _at_Entity
• all fields persistent not marked with _at_Transient
  (configuration by exception)
• persistent once it is associated with an
  EntityManager (em.persist(entity))
• approach refer with annotations to concrete
  tables/columns instead of the abstract
  persistence schema

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Entity Beans

• unidirectional and bidirectional relationships
  attributes of annotations
• one-to-one
• one-to-many
• many-to-one
• many-to-many
• owning side responsible for propagating
  relationship changes to database

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Sample Entity Bean

• _at_Entity public class Employee
• _at_Id(generateGeneratorType.TABLE)
• public Long getId() return id
• public Address getAddress()
• return address
• _at_OneToMany(mappedByleader)
• public ListltEmployeegt getTeamMembers()
• return this.colleagues
• _at_Transient private void getFullName()
• return getFirstName()
  getLastName()

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EJB QL

• EntitiyManager API similar to Hibernate and
  Toplink
• persist(entity), find(Entity.class, id)
• createQuery(ejbqlString), createNativeQuery(sqlStr
  ing)
• EJB QL Examples
• FROM Order order
• SELECT DISTINCT order.address.state FROM Order
  order WHERE order.customer.name LIKE ?
• SELECT order FROM Order order INNER JOIN FETCH
  order.customer

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Enhancements to EJB QL

• explicit inner and outer join
• fetch join for eager loading (defaultlazy)
• bulk update and delete
• subqueries
• group-by
• support for native SQL queries
• dynamic query capability

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Stateless Session Beans

• plain Java object with a class-level annotation
  of _at_Stateless
• can implement the javax.ejb.SessionBean
  interface, but is not required to
• may implement a business interface
• If no business interface implemented, generated
  using all the public methods
• _at_BusinessMethod by default local
• _at_Remote indicates a remote interface

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Sample Stateless Session Bean

• import javax.ejb.
• _at_Stateless
• _at_Remote
• public class HelloWorldBean
• public String sayHello()
• return "Hello World"

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Web Services Session Beans

• JSR-181
• a session bean that serves as a web service
  endpoint is annotated with _at_WebService
• _at_WebMethod used to identify methods that are
  exposed as web service
• other annotations
• _at_WebParam, _at_WebResult, _at_OneWay, _at_SOAPBinding,
  _at_SOAPMessageHandler, _at_HandlerChain, _at_InitParam

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Stateful Session Beans

• similar to Stateless
• lifecycle event callbacks
• _at_PostConstruct after dependency injection
• _at_PreDestroy after method with _at_Remove
• _at_PostActivate equal to ejbActivate()
• _at_PrePassivate equal to ejbPassivate()
• a callback listener class (_at_CallbackListener) may
  be used instead of callback methods

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Sample Stateful Session Bean

• _at_Stateful
• public class AccountManagementBean
• _at_EJB (name"mySessionBean") //dependency
  injection
• private MySessionI myBean
• private Socket socket
• _at_PostConstruct
• _at_PostActivate
• public void initRemoteConnectionToAccountS
  ystem()
• try
• this.socket new Socket,
  PORT)
• catch (Exception ex) throw new
  EJBException(ex)
• ...

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Message-driven Beans

• to a client, a message-driven bean is a message
  consumer
• message-listener business interface determined
  by the messaging type in use
• javax.jms.MessageListener for JMS

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Bean Interfaces

• session beans and message-driven beans require a
  business interface
• interfaces automatically generated from
  implementation, if no interface implemented
• interface name derived from class name
• if several interfaces implemented, annotation
  required to define the business interface
• interfaces assumed local unless annotated

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Client Programming Model

• EJB 3.0 remote or local clients access beans
  through their business interface
• business interfaces are ordinary Java interfaces
• references to business interfaces through
• injection mechanism
• javax.ejb.EJBContext.lookup()
• JNDI API

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Pros and Cons

• less artefacts for developers
• enterprise services for Java core (e.g.JBoss)
• EJB 3.0 compliant desktop application?
• contrary to annotations provide deployment
  descriptors a holistic view to EJB modules
• vendor specific annotations defeats the goal of
  portability
• dont forget about configuration by exception
• entity beans owning side defined by dependent
  sidegt less complexity?