Enterprise Java Beans 3.0

by Sandeep Desai (http://www.thedesai.net)

EJB 3 uses Java Persistence API

Java Persistence API can be used in Java Application does not need J2EE Server like EJB 2

Oracle JDeveloper 10.1.3.1 includes support for creating Java SE EJB3 applications

All annotations have an XML equivalent

Message Bean

Handle message concurrently one bean per message
Supports asynchronous messaging using JMS and Message Oriented Middleware
JMS API can send messages using products like Progress SonicMQ, IBM MQSeries, Oracle Advance Queuing
Messaging can use JCA 1.5 to connect to any messaging source e.g email
@javax.ejb.MessageDrivenBean
implements javax.jms.MessageListener Interface
implement onMessage() method
can interact with Local SessionBean, cannot be tagged remote

Entity Bean

Entity Bean uses @javax.Persistence.Entity,
Primary Key uses @javax.Persistence.Id (can be class or primitive type)
Should only have validation business logic
Table Mapping can be in annotation or XML (XML overrides annotation)
Managed (attached) or Unmanaged (detached)
EntityManager flushes changes to Entity Bean after

Session Bean

Support one client at a time
@javax.ejb.Stateful or @javax.ejb.Stateless
@javax.ejb.Remote or @javax.ejb.Local
Contains Business logic (e.g. transfer funds from once account to another)
Can be Web Service endpoint interface @javax.jws.WebService
default transaction is required
default security is unchecked
Stateful lifecycle

Passivation (Serialize state) @javax.ejb.PrePassivate call method before passivation (e.g close files if any)
Activation @javax.ejb.PostActivate (e.g open files if any)

Stateless lifecycle

No State (note created)
Pooled State
Ready State (@javax.ejb.EJBContext interface is injected)

Persistence Unit (Persistence.xml)

located in META-INF directory
can be in plain jar, EJB-JAR or JAR in EJB-JAR or JAR in WAR file or JAR in EAR file
defines identities and properties of each named persistence unit

persistence.xml

<?xml version="1.0" encoding="windows-1252" ?>

<persistence xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd"

version="1.0" xmlns="http://java.sun.com/xml/ns/persistence">

<persistence-unit name="ejb3test">

<class>net.thedesai.ejb3.Dept</class>

<class>net.thedesai.ejb3.Emp</class>

<property name="toplink.jdbc.url"

value="jdbc:oracle:thin:@localhost:1521:ORCL"/>

<property name="toplink.jdbc.password"

value="3E20F8982C53F4ABA825E30206EC8ADE"/>

</properties>

</persistence-unit>

</persistence>

Persistence Context

set of managed entity object instances. Peristence Contexts are managed by Entity Manager
When persistence context closed, entity beans are detached
two types of persistence contexts

transaction scoped (Persistence Context destroyed at end of transaction and Entity Beans become unmanaged)
extended persistence context used for long running transactions (detached Entity Bean can be serialized and sent over network)

transaction scoped example requires PersistenceContext to be injected

@PersistenceContext(unitName=”foo”)

EntityManager entityManager;

@TransactionAttribute(REQUIRED)

public void updateEmp() {

Employee emp = entityManager.find(Employee.class, 1);

emp.setSalary(1234567);

}

Extend Persistence Context example

Employee emp = null;

transaction.begin();

emp = extendedEntityManager.find(Employee.class, 1);

transaction.commit();

transaction.begin();

emp.setSalary(7654321);

extendedEntityManager.flush();

transaction.commit();

Client Applications

Never access Beans directly only through Proxy

EJB Servers (Primary Services)

Concurrency (don’t create threads or use synchronized)
Transaction management,
Persistence:

1. EntityManager provides method to create, find, query, remove and update beans

2. can attach and detach instance, detached instance can be sent across network

3. manage m:n relationship

4. manage collections

5. @Entity @Table(name=”EMP”) public class Emp {

6. private int id, private String name;

7. @Column(name=”NAME”) ..get() set() .. @Id @Column(name=”ID”) }

Object distribution, support RMI-IIOP and SOAP 1.2 using JAX-RPC

1. Any SOAP Client e.g. .NET can access stateless session bean

Asynchronous Messaging. Server will attempt to redeliver message on failure. Session, Message and Entity Bean can send message
EJB Timer Service (e.g. mortgage payment past due) can be set on all Beans, can be used for batch processing also
Naming (JNDI)

1. javax.naming.Context c = new javax.naming.InitialContext();

2. Object ref = c.lookup(“FooRemote);

3. FooRemote f = PortableRemoteObject.narrow(ref, FooRemote.class);

4. f.doSomething(...);

Security: Authentication, Authorization (access control), Secure Communication (support SSL 3.0 and Transport Layer Security 1.0)
supports instance pooling

Limitations

Supports collection of entities only does not support primitive collections such as Set<Integer>

Books:

Mastering EJB3 (Free ebook on www.serverside.com)
Enterprise JavaBeans 3.0 by Bill Burke and Richard Monsoon Haefal

No Clear instructions on how to run code using Java SE or JBoss

POJOs in Action by Chris Richardson (covers, Hibernate3, EJB3 and JDO)

No clear instructions on how to run code

Links