Enterprise Java Bean 3.0

Kelum Senanayake

Yet Another Introduction…

Tag-Cloud

EnterpriseJavaBeans

POJO JavaPersistenceAPI

StatelessSessionBean

StatefulSessionBean

Annotations

EntityBean

ResourceInjection

MessageDrivenBean

JavaEE

Transactions

Enterprise Java Beans

Enterprise Java Beans (EJB)

• A platform for building portable, reusable, and scalable business applications.

• Allows to focus on building business logic without having to spend time on building infrastructure code for services such as transactions, security, automated persistence.

• An EJB is a piece of Java code that executes in a specialized runtime environment.

EJB as a component …

• A component should effectively encapsulate application behavior.

• All we need to know is what to pass in and what to expect back.

• Components can be reusable.

• Three types of EJB components: – Session beans

– Message-driven beans

– Entities

EJB as a framework …

• EJB components live in a container.

• Together, the components, or EJBs, and the container can be viewed as a framework.

• EJB framework provides valuable services for enterprise application development

EJB History

• EJB 1.0 (1998-03-24)

– Defined the responsibilities of EJB Container provider

– Defined the distinct “EJB Roles”

• EJB 1.1 (1999-12-17)

– XML deployment descriptors

– Session Beans, Entity Beans

– Remote interface

• EJB 2.0 (2001-08-22)

– Message-Driven Beans

– Entity 2.x and EJB QL

EJB History …contd

• EJB 2.1 (2003-11-24) – EJB Timer Service – Web service support

• EJB 3.0 (2006-05-11) – POJO, Annotations – Dependency injection

• EJB 3.1 (2009-12-10) – Local view without interface – .war packaging of EJB components – Singletons (Singleton Session Beans) – EJB Lite: definition of a subset of EJB – @Asynchronous for session beans

EJB 3.0 vs EJB 2.1

• EJB 3.0 is much faster than EJB 2 • An EJB 2.1 session bean must implement the

SessionBean interface • EJB 3.0 session bean class includes only business

methods. • EJB 3.0 interfaces are POJI business interfaces

and do not require home and component interfaces.

• EJB 2.1 must have the deployment descriptor. But optional in EJB 3.0. Annotations are added to the language.

EJB 3.0 vs EJB 2.1 …contd

• EJB 3 introduced persistence API for database access. In EJB 2 you can use Entity bean.

• An EJB 2.1 Entity EJB bean class must implement the EntityBean interface and must provide implementation to the ejbCreate() and ejbPostCreate() methods.

• EJB 2.1 entity bean includes the home, component, local home and local component interfaces that extend the EJBHome, EJBObject, EJBLocalHome and EJBObject interfaces respectively.

• An EJB 2.1 bean must define resource-ref in ejb-jar.xml to lookup resources. An EJB 3.0 bean can use either dependency injection or JNDI lookup.

• An EJB 2.1 message-driven must implement the javax.ejb.MessgeDrivenBean interface.

• Standardized Simplified persistence with POJO

– You couldn’t send an EJB 2 entity bean across the wire in different tiers.

– They are permanently attached to the database.

– You have to write data transfer objects

EJB 3.0 vs EJB 2.1 …contd

Why choose EJB 3.0?

• Ease of use – POJO programming, annotations in favor of verbose

XML, heavy use of sensible defaults & JPA

• Integrated solution stack – EJB 3 offers a complete stack of server solutions

– Persistence, messaging, lightweight scheduling, remoting, web services, dependency injection (DI) and interceptors

– You won’t have to spend a lot of time looking for third-party tools

Why EJB 3.0 …contd

• Open Java EE standard

– EJB is a critical part of the Java EE standard

– EJB 3 has an open, public API specification

– The open standard leads to broader vendor support

– You don’t have to depend on a proprietary solution

Why EJB 3.0 …contd

• Broad vendor support – You are not at the mercy of the ups and downs of

a particular company or group of people

– Vendors have historically competed against one another by providing value-added nonstandard features

• Stable, high-quality code base – Clustering, load balancing, and failover support

with no changes to code, no third-party tool integration, and relatively simple configuration

Why EJB 3.0 …contd

• Unit-testable POJO components – All EJB 3 components are POJOs, they can easily

be executed outside the container

– It is possible to unit-test all component business logic using testing frameworks

• Annotations and descriptors are not mutually exclusive – Deployment descriptor entries override

configuration values hard-coded into EJB components

JavaEE Container

The Container

• When you build a simple Java class, you need a Java Virtual Machine (JVM) to execute it.

• Think of the container as simply an extension of the basic idea of a JVM.

• JVM transparently manages memory on your behalf.

• The container transparently provides EJB component services – Transactions, security management – Remoting and web services support

Container …contd

• A Java EE container is an application server solution that supports EJB 3, a web container, and other Java EE APIs and services.

• JPA is completely pluggable and separable.

– Persistence provider and container in an EJB 3 solution need not come from the same vendor

– You could use Hibernate inside a BEA WebLogic container

Hello World !

HelloUser Example

HelloUser Example (Client)

Dependency injection vs. JNDI lookup

• With EJB 2, you have to write the same few lines of boilerplate code many times to do a JNDI lookup.

• In EJB 3, JNDI lookups have been turned into simple configuration using metadata-based dependency injection (DI)

• JNDI : It’s the responsibility of the client to do a lookup and obtain a reference to the object

• You may think DI is the opposite of JNDI – It is the responsibility of the container to inject an

object based on the dependency declaration

Building business logic with Session Beans

Getting to know Session Beans

• So what is a Session? – A session is a connection between a client and a

server that lasts for a finite period of time

• Session beans centers on the idea that each request by a client to complete a distinct business process is completed in a session.

• Recall that session beans come in two flavors: Stateful and Stateless

• A bean may maintain its state between calls, in which case it is stateful, or it may be a one-time call, in which case it’s stateless.

@Stateless Session Bean

• No more Home interfaces!

• A POJI Business Interface

– Annotated with @Remote or @Local

• A POJO Implementation

– Annotated with @Stateless

• No more deployment descriptors! (optional)

@Stateful Session Bean

• No more Home interfaces!

• A POJI Business Interface

– Annotated with @Remote or @Local

• A POJO Implementation

– Annotated with @Stateful

• No more deployment descriptors! (optional)

Working with multiple business interfaces

• You cannot mark the same interface with more than one access type annotation.

• However, a business interface can extend another interface.

• You can create a set of interfaces utilizing OO inheritance to avoid code duplication

Callback methods

• @PostConstruct

• @PostActivate

• @PrePassivate

• @PreDestroy

@MessageDriven Bean

Messaging with message-driven beans

Diving into the Java Persistence API

Java Persistence API

• Separate specification document

• Produced by EJB 3.0 Expert Group (JSR-220)

• Available in & outside the Java EE container

• The API itself, defined in the javax.persistence package

• The Java Persistence Query Language (JPQL)

• Object/relational metadata

• Gavin King (founder of Hibernate) represented JBoss on JSR220

@Entity Beans

• No more Home interfaces!

• No Business Interfaces!

• A POJO Implementation

– Annotated with @Entity

• A simple deployment descriptor

• Entities need not use getter- and setter-based properties.

EntityManager

• EntityManager is the bridge between the OO and relational worlds.

• Knows how to store a POJO entity into the database, read, update & delete.

• Factory for Query

Query

entityManager.createNativeQuery()

Named queries

• They improve reusability of queries.

• They improve maintainability of code

– Queries are not scattered among the business logic.

• They can enhance performance because they are prepared once and can be efficiently reused.

• Can be defined either in the entity using annotations, or in the XML file defining O/R mapping metadata.

Transaction Management

Understanding transactions

• A transaction is a grouping of tasks that must be processed as an inseparable unit.

• Every task that is part of the transaction must succeed in order for the transaction to succeed. All-or-nothing

• The Transaction Manager is a component that, coordinates a transaction over multiple distributed resources

• EJB provides through the Java Transaction API (JTA)

Container-managed transactions

• In a CMT, the container starts, commits, and rolls back a transaction on our behalf

• Can be done through annotations or the deployment descriptor

• EJB context: accessing the runtime environment

• The javax.ejb.EJBContext interface is essentially your backdoor into the mystic world of the container

Bean-managed transactions

• The greatest strength of CMT is also its greatest weakness.

• CMT, you are limited to having the transaction boundaries set at the beginning and end of business methods and relying on the container to determine when a transaction starts, commits, or rolls back.

• BMT, on the other hand, allows you to specify exactly these details programmatically

The pros and cons of BMT

• BMT is verbose, complex, and difficult to maintain and some times error prone.

• With BMT, you can fine-tune your transaction boundaries so that the data held by your code is isolated for the shortest time possible

• BMT can never join an existing transaction.

– Existing transactions are always suspended

– Significantly limiting flexible component reuse

References

• [1] D. Panda, R. Rahman, and D. Lane, EJB 3 in Action, 1st ed. Manning Publications, 2007.

• [2] “Enterprise JavaBeans - Wikipedia, the free encyclopedia.” [Online]. Available: http://en.wikipedia.org/wiki/Ejb. [Accessed: 10-Mar-2012].

• [3] “What I’m Learning: Differences between EJB 3.0 and EJB 2.1.” [Online]. Available: http://mytechnicaldocs.blogspot.com/2011/08/differences-between-ejb-30-and-ejb-21.html. [Accessed: 10-Mar-2012].

@Questions?