These slides were used for the module "Introduction to EJB" which was taught as a part of the course "Software Engineering" for the 3rd year computer enigneering undergraduates of the University of Peradeniya in 2010.

1. Introduction to Enterprise Java
Beans [EJB]
Lecture Series Under IFS-PERA collaboration
[2010]
Tharindu Weerasinghe [MSc.Eng, BSc.Eng (Hons), MIEEE, AMIESL]
Software Engineer, IFS R&D International
© 2010 IFS

2. EJB Framework - Overview
What is EJB?
❑ Enterprise Java Beans are the Java EE server
side components that run inside the EJB container
and encapsulates the business logic of an
enterprise application.
❑It is an architecture for server-side component
based distributed applications written in Java.

3. Basic EJB Environment

4. Contents of the EJB environment
➢ The EJB components are running inside the container of an
EJB server.
➢ The container has the connection to the database or to
other components.
➢ An EJB client can access the EJBs from the same Java
Virtual Machine (JVM) or from another JVM over remote
interfaces. The EJB home component is comparable to a
factory for the EJB objects. The EJB objects retrieved from the
home components can be also local or remote objects.

5. Why EJB ?
➢Numerous Web sites are up and running using Java without
any EJB technology. Developers have been using servlet/JSP
models and managing transactions themselves using commit
and rollback functionality that is built into JDBC without the
help of application servers.
➢But when doing so, the application developers are
confronted with many challenges. Some of the most important
ones are managing concurrency, persistence and
transactions. As a result, the developers have to either
develop proprietary code or buy supporting frameworks.

6. Why EJB ?
➢Above problems are solved by using enterprise beans.
The use of enterprise beans allow developers to focus on
the business logic and release them from coding
infrastructure and middleware logic, and developers
become more productive and efficient.

7. Benefits of EJB
➢EJB container provides the system-level services (like
transaction management and security authorization) to the
enterprise beans. These services simplifies the development
process of large and distributed applications and the
developer just have to concentrate on solving the problem
occurred in it.
➢The client developer can focus only on the representation
style of the client as all the business logic of the application is
contained in the enterprise beans. The client developer does
not bother about the code that implements business logic or
the logic to access the databases. This means that the
clients are thinner. It benefits the client to be thin because
the client runs on the small devices.

8. When to use EJB?
Applications developed by using the EJB, deal with a variety of
clients, simply by writing few lines of code, the client can
locate the enterprise beans. The client locating the enterprise
bean may be various, numerous and thin.
Enterprise beans support transaction to ensure the integrity of
the database. Transaction is the mechanism of managing the
concurrent access of shared objects.
Managing the fast growing number of users requires
distributed application components across multiple machines
means that the application must be scalable.

9. EJB Roles
Bean provider
The bean provider is the developer of the code, and is
responsible for converting the business requirements into
actual physical code. He or she must provide the necessary
classes that constitute an EJB, as well as providing the
deployment file describing the runtime settings for the bean.
The bean provider’s final product is an EJB JAR file.
(Most of you guys/gals fall into this category ☺)

10. EJB Roles
Application assembler
This may be the same as the bean provider, or a senior team
lead. The application assembler’s responsibility is to package
all the different EJB components, along with any other
application components, the final product being an enterprise
application EAR file.
Deployer
This person is responsible for deploying the EJB application on
the target runtime environment. The deployer should be
familiar with all aspects of the environment, including
transaction and security support.

11. EJB Roles
Server provider
The job of the server provider is to provide a runtime EJB
server environment that is compliant with the EJB
specification. IBM is a server provider of the WebSphere
Application Server.
Container provider
The job of the container provider is to provide a runtime EJB
container environment that is compliant with the EJB
specification, and is generally the same as the server provider.
The server and container cooperate to provide the quality-of-
service runtime environment for the EJBs.

12. EJB Roles
Systems administrator
The system administrator’s task is to ensure that the runtime
environment is configured in such a way that the application
can function correctly, and is integrated with all of the required
external components.

13. MAIN EJB FRAMEWORK COMPONENTS
❑EJB server
Provides the actual primary services to all EJBs. An EJB server
may host one or more EJB containers. It is also called
generically an Enterprise Java Server (EJS). WebSphere
Application Server is an EJS.
❑EJB container
Provides the runtime environment for the enterprise bean
instances, and is the intermediary between the EJB
component and the server.

14. MAIN EJB FRAMEWORK COMPONENTS
❑ EJB component
These represent the actual EJBs themselves. There are three
types of enterprise beans: entity, session, and message-driven
beans.
❑EJB interfaces and EJB bean
The interfaces for client access (EJB home and EJB object)
and the EJB bean class.

15. MAIN EJB FRAMEWORK COMPONENTS
❑EJB deployment descriptor
The descriptor defines the runtime quality of service settings
for the bean when it is deployed. Many of the settings of an
EJB, such as the transactional settings, are defined in the
deployment descriptor. The deployment descriptor is an
external entity from the bean, and therefore decouples the
bean component itself from the runtime characteristics.
❑EJB client
A client that accesses EJBs.

16. WE TALK MORE ON
EJB COMPONENTS
© 2009 IFS

17. EJB COMPONENTS
❑The EJB components refer to the beans themselves, and
include all the classes, interfaces, and constructs that make
up the enterprise bean.
❑There are three types of enterprise beans:
➢Entity
➢Session
➢Message-driven
❑The rules for bean construction (which interfaces to use,
classes to extend, and so forth) are governed by the type of
bean, so a quick introduction to the types of enterprise beans
is presented here.

18. MAIN EJB FRAMEWORK COMPONENTS

19. EJB TYPES
❑Entity Beans:
Entity beans are modeled to represent business or domain-
specific concepts, and are typically the nouns of your system,
such as customers and accounts. They usually represent data
(entities) stored in a database.
❑Session Beans:
A session bean is modeled to represent a task or workflow of a
system, and provide coordination of those activities between
beans, such as a banking service, allowing for a transfer
between accounts.

20. EJB TYPES
Session beans have two types:
1. Stateful Session Beans
2. Stateless Session Beans
❑Message-driven beans
Like session beans, message-driven beans (MDB) may also be
modeled to represent tasks. However, they are invoked by the
receipt of asynchronous messages. The bean either listens for
or subscribes to messages that it is to receive.

21. SYNCHRONOUS VS ASYNCHRONOUS INVOCATION
Entity and Session beans are accessed synchronously through
a remote or local EJB interface method invocation. This is
referred to as synchronous invocation, because there is a
request, and a (blocking) wait for the return.
Clients of EJBs invoke methods on session and entity beans.
An EJB client may be an external construct like a servlet
(remote) or another EJB within the same JVM (local).

22. SYNCHRONOUS VS ASYNCHRONOUS INVOCATION
The Message-driven bean is not accessible through a remote
or local interface. The only way for an EJB client to
communicate with a message-driven bean is by sending a JMS
message.
This is an example of asynchronous communication. The client
does not invoke the method on the bean directly, but rather,
uses JMS constructs to send a message. The container
delegates the message to a suitable message-driven bean
instance to handle the invocation.

23. SPECIAL MENTION:
All on-line material referred when preparing these slides.
© 2009 IFS

24. www.IFSWORLD.com
THIS DOCUMENT MAY CONTAIN STATEMENTS OF POSSIBLE FUTURE FUNCTIONALITY FOR IFS’S SOFTWARE PRODUCTS AND
TECHNOLOGY. SUCH STATEMENTS OF FUTURE FUNCTIONALITY ARE FOR INFORMATION PURPOSES ONLY AND SHOULD NOT BE
INTERPRETED AS ANY COMMITMENT OR REPRESENTATION. IFS AND ALL IFS PRODUCT NAMES ARE TRADEMARKS OF IFS. THE
NAMES OF ACTUAL COMPANIES AND PRODUCTS MENTIONED HEREIN MAY BE THE TRADEMARKS OF THEIR RESPECTIVE OWNERS.
© 2009 IFS