Enterprise Java Bean 3.0
Filippo Diotalevi
http://www.diotalevi.com
filippo.diotalevi@jugmilano.it
Java User Group Milano
http://www.jugmilano.it
February 16th, 2006

Filippo Diotalevi
http://www.diotalevi.com/weblog
https://java-champions.dev.java.net/
http://www.jugmilano.it
JUG Milano – EJB 3.0 3

Tag-Cloud
StatelessSessionBean
ResourceInjection
EnterpriseJavaBeans
StatefulSessionBean
EntityBean
POJO
MessageDrivenBean
JavaEE5
Annotations JavaPersistenceAPI
Glassfish
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JavaEE5
Goals • EOD – Easy of Development
• Increase productivity
• Full backward compatibility
• Community involvement
ResourceInjection
Tools: POJO
Annotations
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JavaEE5: Key new Specs
• Java Persistence API (JSR-220)
• EJB 3.0 (JSR-220)
• JavaServer Faces (JSR-252)
• JAX-WS (JSR-224)
• JAXB (JSR-222)
• Common Annotations (JSR-250)
• StAX (JSR-173)
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EJB History
EJB 1.1 ( J2EE 1.2 ), 1999
• Session beans (stateless & stateful), Entity Beans
• Remote interface
EJB 2.0 ( J2EE 1.3 ), 2001
• Message-Driven Beans
• Entity 2.x and EJB QL
• Local and Remote interfaces
EJB 2.1 ( J2EE 1.4 ) 2003
• EJB Timer Service
• Minor EJB QL enhancements
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EJB 2.x Problems
• “Noisy”
• Metadata XML Hell
• Difficult test
• Not truly OO
• Pattern proliferation (DTO, Service
Locator, ...)
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EJB 3: Solutions
• POJO Model
• Annotations
• “Configuration by exception”
• Java Persistence API
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@Stateless Session Bean
• No more Home interfaces!
• A POJI Business Interface (optional!)
Annotated with @Remote or @Local
• A POJO Implementation
Annotated with @Stateless
• No more deployment descriptors! (optional)
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@Stateless Session Bean
public interface Calculator
@Remote
{
@Local
public int sum(int a, int b);
..or default (@Local)
}
@Stateless
public class CalculatorImpl implements Calculator
{
public int sum(int a, int b)
{
return a + b;
}
}
JUG Milano – EJB 3.0 11

Transaction Management
@Stateless
public class CalculatorImpl implements Calculator
{
@TransactionAttribute(TransactionAttributeType.REQUIRES_NEW)
public int sum(int a, int b)
{
//....
}
TransactionAttributeType.MANDATORY
TransactionAttributeType.REQUIRED
TransactionAttributeType.REQUIRES_NEW
TransactionAttributeType.SUPPORTS
TransactionAttributeType.NOT_SUPPORTED
TransactionAttributeType.NEVER
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@Stateful Session Bean
• No more Home interfaces!
• A POJI Business Interface (optional!)
Annotated with @Remote or @Local
• A POJO Implementation
Annotated with @Stateful
• No more deployment descriptors! (optional)
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@Stateful Session Bean
@Local
public interface CounterEjb {
public int count();
public void reset();
}
@Stateful
public class CounterEjbImplementation implements CounterEjb {
private int count = 0;
public int count() {
return ++count;
}
public void reset() {
count = 0;
}
}
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Other features
Callback methods @PostConstruct
@PostActivate
@PrePassivate
@PreDestroy
@Interceptors
Declare interceptor classes (@Interceptors)
Develop an interceptor (POJO!)
Annotate interceptor's methods with @AroundInvoke
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EJB Invocation & dependency injection
public class CountServlet extends HttpServlet{
@EJB
public CounterEjb counter;
protected void doGet(HttpServletRequest req,
HttpServletResponse res) throws ServletException,IOException
{
counter.count();
}
}
Dependency injection can only be used by managed classes
Servlet, listener classes, web services end-point,
JAX-RPC handlers, EJB, interceptors, web services
end-point
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Java Persistence API
• Separate specification document
• Produced by EJB 3.0 EG
(JSR-220)
• Available in & outside the
Java EE container
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@Entity Beans
• No more Home interfaces!
• No Business Interfaces!
• A POJO Implementation
Annotated with @Entity
• A simple deployment descriptor
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@Entity Beans
@Entity
public class Item implements Serializable{
private Long id;
Id auto generation
private String name;
Primary Key
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
public Long getId() { return id; }
public void setId(Long id) { this.id = id; }
public String getName() { return name;}
public void setName(String name) { this.name = name; }
}
(if not transient) Properties are automatically persisted
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EntityManager
• A detyped “home” interface
• create(), merge() and
remove() instances
• Factory for Query
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EntityManager
@Stateless
public class PaginaDAOImpl implements PaginaDAO {
@PersistenceContext EntityManager entityManager;
public void salva(Pagina pagina) { EntityManager injected!
entityManager.merge(pagina);
}
public void elimina(Pagina pagina) {
entityManager.remove(pagina);
}
public Pagina leggi(String titolo) {
Pagina p = entityManager.find(Pagina.class, titolo);
}
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@PersistenceContext ?
persistence context as \"a set of entity
instances in which - for any persistent entity
identity -there is a unique entity instance.\"
A persistence unit is
persistence unit #2
a set of classes that
are mapped to a
single data store
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Query
Query query = entityManager.createQuery(\"SELECT p FROM Pagina p\");
return query.getResultList();
• Query parameters
• Support for pagination
• Native query
entityManager.createNativeQuery()
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Deployment Descriptor
Need to define the Persistence Unit in persistence.xml
<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<persistence xmlns=\"http://java.sun.com/xml/ns/persistence\">
<persistence-unit name=\"defaultPersistenceUnit\"
transaction-type=\"JTA\">
<jta-data-source>jdbc/__default</jta-data-source>
<properties>
<property name=\"toplink.platform.class.name\"
value=\"oracle.toplink.essentials.platform.database.DerbyPlat
form\"/>
</properties>
</persistence-unit>
</persistence> Glassfish configuration
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Entity Beans: advanced features
• Associations
@OneToOne
@OneToMany
@ManyToOne
@ManyToMany
• Support for inheritance
@Inheritance > 3 inheritance strategies: SINGLE TABLE
TABLE PER CLASS
JOINED TABLES
• Support for “cascadable” associations (@Cascade)
• Support for optmistic locking (@Version)
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EJB Query Language
• Very similar to HQL (Hibernate Query Language)
• Support for polymorphic queries
• Support for native queries
• Subselects
UPDATE Customer c
SET c.status = 'outstanding'
WHERE c.balance < 10000
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@MessageDriven Bean
• The Business Interface is the message
listener interface (for JMS, javax.jms.MessageListener)
• A POJO Implementation
Annotated with @MessageDriven
• No more deployment descriptors! (optional)
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Open Source EJB3 Implementations
https://glassfish.dev.java.net/
http://www.jboss.org
http://jonas.objectweb.org/
To be released: Open JPA (Solarmetric KODO)
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@Questions?
Thank you!
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References
• JSR 220: Enterprise JavaBeansTM 3.0
http://www.jcp.org/en/jsr/detail?id=220
• Glassfish website and documentation
https://glassfish.dev.java.net
• JBoss website and documentation
http://www.jboss.org
• Gavin King's “Entity Beans in EJB 3”
http://hibernate.org/gavin/ebejb3.pdf
• Kenneth Saks “Enterprise Java Bean 3.0”
http://www.javasig.com/Archive/lectures/JavaSIG-EJB30.pdf
• Filippo Diotalevi's “Java EE 5 – Step by Step”
http://www.diotalevi.com/weblog/?page_id=125
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